A VFD Receiver (Triodes in Disguise)
Created by on 2009-01-22A VFD (Voltage Fluorescent Device) Regenerative Receiver built in "retro" 1930's style.
Background to this project.
Valves/Vacuum Tubes and "Triodes in Disguise".
VFD's used as Valves/Vacuum Tubes.
Receiver Description.
The R.F. and Detector stage schematics.
A.F. Stage Schematics.
Receiver Construction and Pictures.
Test Results.
MP3 Audio Clips.
Final Comments.
References and Links.
A link to my web-page with more images and detail about this project.
Thereis a great deal of "folklore" surrounding regenerative receiverswith claims of exceptionally good performance from these simpledesigns. For the most part these claims are well justified. Its true tosay that a well constructed regen receiver of good design will givepleasing performance. Over the years a number of regen receivershave been constructed here at M0AYF for both broadcast and ham radioreception using vacuum tubes and/or solid state devices.I can confirm that they do indeed perform as advertised. Butmost of thereceivers built here had taken advantage of using moderncomponents and construction techniques so it was interesting to buildthe "retro" receiver using more traditional construction techniques andthen to compare the performance to that of newer designs.
In order to remain as faithful as possible to the traditional methodsof construction and technology available in the 1930's it was decidedthat low-mu (low gain) triodes would be used for the various stages ofthe receiver. Though I have a small quantity of 1930's triodevalves/tubes in the M0AYF junk-box the decision was made to save thesefor a future "retro" project. So a suitable active device to serveas a replacement for the low-mu triodes had to be found. Physicalinspection of the internal construction of a VFD (Voltage FluorescentDevice) revealed that it possessed all of the key electrodes found in atriode valve/tube.
Valves/Vacuum Tubes and "Triodes in Disguise"
A basic triode valve/tube consists of three electrodes, a heatedcathode, a control grid and an anode/plate. The cathode electrodein a typical directly heated triode takes the form of a speciallycoated filament. This coated filament is arranged such that when an electriccurrent is passed through it the filament will heat up and "glow"causing electrons to be freely emitted. This is generally termed a"directly heated" or "self heated" cathode. Below is a cut-away diagram of a triodevalve/tube which is of the directly heated type and typical ofthose used in the 1930's for domestic broadcast receivers.
In the image (above right) of the VFD tube "lit-up" both the grid mesh and the two filament wires are clearly visible.
The internalelectrodes of the the VFD device are shown in the diagram on the right.The phosphor coated anodes/plates have separate connections so thatindividual segments can be switched on or off to produce differentnumbers.
Valves/Vacuum Tubes and "Triodes in Disguise".
VFD's used as Valves/Vacuum Tubes.
Receiver Description.
The R.F. and Detector stage schematics.
A.F. Stage Schematics.
Receiver Construction and Pictures.
Test Results.
MP3 Audio Clips.
Final Comments.
References and Links.
A link to my web-page with more images and detail about this project.
Background to this project.
Thislittle project arose from a desire to experiment with some of the more"traditional" methods of radio construction which enjoyedpopularity some 70 years ago. I wanted to find out for myself what kindof performance could be achieved using simple circuits incorporatingValves/Vacuum Tubes and low budget design techniques popular in the1930's. In particular I was curious to try out "Spider" coils and aRegenerative Detector using a low-mu (low gain) triode as the activedevice.
Thislittle project arose from a desire to experiment with some of the more"traditional" methods of radio construction which enjoyedpopularity some 70 years ago. I wanted to find out for myself what kindof performance could be achieved using simple circuits incorporatingValves/Vacuum Tubes and low budget design techniques popular in the1930's. In particular I was curious to try out "Spider" coils and aRegenerative Detector using a low-mu (low gain) triode as the activedevice.
Thereis a great deal of "folklore" surrounding regenerative receiverswith claims of exceptionally good performance from these simpledesigns. For the most part these claims are well justified. Its true tosay that a well constructed regen receiver of good design will givepleasing performance. Over the years a number of regen receivershave been constructed here at M0AYF for both broadcast and ham radioreception using vacuum tubes and/or solid state devices.I can confirm that they do indeed perform as advertised. Butmost of thereceivers built here had taken advantage of using moderncomponents and construction techniques so it was interesting to buildthe "retro" receiver using more traditional construction techniques andthen to compare the performance to that of newer designs.
In order to remain as faithful as possible to the traditional methodsof construction and technology available in the 1930's it was decidedthat low-mu (low gain) triodes would be used for the various stages ofthe receiver. Though I have a small quantity of 1930's triodevalves/tubes in the M0AYF junk-box the decision was made to save thesefor a future "retro" project. So a suitable active device to serveas a replacement for the low-mu triodes had to be found. Physicalinspection of the internal construction of a VFD (Voltage FluorescentDevice) revealed that it possessed all of the key electrodes found in atriode valve/tube.
Valves/Vacuum Tubes and "Triodes in Disguise"
A basic triode valve/tube consists of three electrodes, a heatedcathode, a control grid and an anode/plate. The cathode electrodein a typical directly heated triode takes the form of a speciallycoated filament. This coated filament is arranged such that when an electriccurrent is passed through it the filament will heat up and "glow"causing electrons to be freely emitted. This is generally termed a"directly heated" or "self heated" cathode. Below is a cut-away diagram of a triodevalve/tube which is of the directly heated type and typical ofthose used in the 1930's for domestic broadcast receivers.
A Voltage Fluorescent Device (VFD) is a display device used extensivelyin domestic electrical goods such as VCR's, bedside clocks andmicrowave ovens to name but a few. Though it may not be immediatelyobvious the internal construction of a VFD is very similar to that of asimple directly heated triode valve/tube, a sort of "Triode in Disguise". The main difference is thatthe VFD is of a planar construction which is in contrast to thecoaxial construction of the typical valve/tube shown in the diagram above. TheVFD's used in this project contain a single 7-segment display within aglass envelope and physically resemble a small valve/vacuum tube. TheVFD has a directly heated cathode (filament wires), a control grid andat least one anode/plate coated with a phosphor which emits light whenstruck by electrons. Most VFD's have more than one phosphor coatedanode/plate each with its own electrical connection to provide a multisegmented display. For example a "numbers" display would typically haveat least seven phosphor coated anodes/plates and possibly a few more toindicate the sign and decimal place.
Twoexample images of the VFD's used in the retro receiver are shown below.
Twoexample images of the VFD's used in the retro receiver are shown below.
In the image (above right) of the VFD tube "lit-up" both the grid mesh and the two filament wires are clearly visible.The internalelectrodes of the the VFD device are shown in the diagram on the right.The phosphor coated anodes/plates have separate connections so thatindividual segments can be switched on or off to produce differentnumbers.
In the example VFD shown above the filament supply Voltage is around1.5 to 2 Volts and when used as a number display the anode/plateVoltage is about +40 Volts. In multi-VFD's (those able to display morethan one digit at a time) the filament Voltage is generally higher at 4to 6 Volts though the anode/plate Voltages are still of the order of+40 Volts or so. The component parts of the seven segment VFD displayshown above are enclosed in a transparent glass envelope from which allthe gas has been removed. i.e. A "hard" vacuum just like that of thetriode valve example mentioned earlier.
All the VFD displays I have encountered have only one set offilaments for the whole display regardless of the number of digits orcharacters it may have. In normal display applications the filamentwill be run from an AC supply. However, for use in radio work it isnecessary to use a DC supply for the filaments. This is because an ACsupply would cause an unwanted signal to be introduced into thecircuit. Using a DC supply for the filaments does not pose a majorproblem when using single digit/character displays but with multi-digitdisplays within a single glass envelope (such as those found in a VCR)the effect of the DC filament supply is to produce a "potentialgradient" across the display. The effect of this potentialgradient is to cause the brilliance of the display to be uneven acrossthe total display area. The reason this happens is because the currentpassing through the filament wires causes a progressive Voltage dropalong the filament wires which acts as a progressively increasing biasto the individual sections of the display.
For example, in a VFDdisplay with say five separate sections enclosed in a single glassenvelope side-by-side (such as a clock display for a VCR) you wouldexpect to see a significant difference in brightness from one one endof the display to the other due to the potential gradient effect. If the filament supply was say +6 Voltsthen the section of the display nearest the 0 Volt end of the filamentwires would be the brightest while the section at the +6 Volt end ofthe filament wires would be darker. Its the same as putting anincreasing positive bias on the cathode of a valve/vacuum tube, thegreater the positive bias on the cathode the more the current in thevalve/tube reduces. A picture of a five section VFD display using a DCfilament supply showing the effect of potential gradient can be seenbelow.
All the VFD displays I have encountered have only one set offilaments for the whole display regardless of the number of digits orcharacters it may have. In normal display applications the filamentwill be run from an AC supply. However, for use in radio work it isnecessary to use a DC supply for the filaments. This is because an ACsupply would cause an unwanted signal to be introduced into thecircuit. Using a DC supply for the filaments does not pose a majorproblem when using single digit/character displays but with multi-digitdisplays within a single glass envelope (such as those found in a VCR)the effect of the DC filament supply is to produce a "potentialgradient" across the display. The effect of this potentialgradient is to cause the brilliance of the display to be uneven acrossthe total display area. The reason this happens is because the currentpassing through the filament wires causes a progressive Voltage dropalong the filament wires which acts as a progressively increasing biasto the individual sections of the display.
For example, in a VFDdisplay with say five separate sections enclosed in a single glassenvelope side-by-side (such as a clock display for a VCR) you wouldexpect to see a significant difference in brightness from one one endof the display to the other due to the potential gradient effect. If the filament supply was say +6 Voltsthen the section of the display nearest the 0 Volt end of the filamentwires would be the brightest while the section at the +6 Volt end ofthe filament wires would be darker. Its the same as putting anincreasing positive bias on the cathode of a valve/vacuum tube, thegreater the positive bias on the cathode the more the current in thevalve/tube reduces. A picture of a five section VFD display using a DCfilament supply showing the effect of potential gradient can be seenbelow.
Oneof the reasons that VFD's have enjoyed widespread use for so long isthat they produce a bright display with a wide viewing angle. The spectrumfrom the display is also fairly wide for any given colour giving asofter light which is pleasing to the eye. In recent years the VFD hasbeen increasingly replaced by L.E.D. and/or L.C.D. displays which continue to developand offer higher efficiency, longer life and are physically more ruggedthan the VFD.
For more information on V.F.D.'s see references 1,2,3 and 6 in the "References and Links" section at the bottom of this page.
VFD's used as Valves/Vacuum Tubes.
The receiver described here follows mostly tried and trusted methods ofconstruction with one major exception, VFD's have been used in place ofvalves/vacuum tubes in order to simulate low-mu triodes and to satisfymy own curiosity regarding the use of VFD's for non displayapplications.
Single VFD tubes (sometimes described as "first generation" VFD's) salvaged from an old desk-top calculator have beenused because they seemed well suited for constructing the individualstages of the receiver on a one tube/VFD per stage basis. In each caseall the anodes/plates (seven segments plus decimal point) of thetubes/VFD's have been strapped together to form a single anode/plateconnection. In tests this arrangement seemed to give the bestperformance. Though there is some evidence of the potential gradienteffect mentioned earlier it caused no problems in practice aside from avery slight non uniformity of brilliance over the display area. Indeed,if you look at this "VFD Lit-Up"image it is hard to see any significant difference in brightnessbetween the top and bottom of the display. Using single tubes/VFD'salso permits physical separation of the individual stages of thereceiver which makes it easier to achieve good stability.
First tests using VFD's in place of triode valves/tubes did not lookvery promising. In normal display operation a VFD may have only +40Volts on its anodes/plates and in order to secure sufficient currentflow and display brightness they often resort to some positive Voltagebias applied to the control grid which in turn permits some controlgrid current to flow. This mode of operation is quite satisfactory fordisplay purposes but is not well suited for small signal amplification.
For the initial tests I used a +40 Volt DC supply for the anodes/platessince this is the Voltage which had been used in the desk-top calculatorfrom which the VFD's had been salvaged. I joined all the anodes/platestogether to form a single anode/plate connection. A resistor in theanode was chosen to limit the current to a safe value of around 100micro amps for testing. This was about the same value of current usedfor each individual segment of the display when used in the calculatorand provided a bright display.
With +40 Volts on the anodes I could not get the VFD's to workcorrectly as a small signal amplifier. Indeed, with the control gridconnected to zero Volts via a one mega-Ohm resistor little or nocurrent would flow from the filament to the anodes/plates. Increasingthe anode/plate Voltage to +120 Volts improved matters and I could now see somesigns of current flow (glowing anodes/plates) and signs ofamplification. Finally I increased the HT supply to +200 Volts (andalso increased the value of the anode load resistor) at which point theVFD device began behaving much like a valve/vacuum tube.
Receiver Description.
Thereceiver is a "regenerative" type or (if you prefer) "straight"setwith some controlled positive feedback applied to enhance theselectivityand sensitivity. This type of receiver was very popular in the 1930'sand still finds favour today among radio enthusiasts. Since the VFD'sare in a triode format it means that all the stages of the receiverwould have to use circuitry best suited to the triode configuration. Though the gain of the individual tubes is quite low they areelectrically very "quiet" resulting in a good signal-to-noise ratio. This is also true of "real" triode valves/tubes.
The configuration chosen for the receiver is a 1-V-2 arrangement, thatis, one stage of RF amplification followed by a regenerative detectorstage and two stages of audio frequency amplification. The set-up is asfollows...
R.F. stage = single neutralized triode/VFD.
Detector stage = single triode/VFD.
First A.F. (preamplifier) stage = single triode/VFD.
Second A.F. stage = two triodes/VFD's wired in parallel.
The R.F. stage.
The use of an R.F. stage in a regenerative receiver is oftenmisunderstood. When correctly implemented the regenerative detector isexceptionally sensitive and has no need of additional R.F.amplification below frequencies in the upper H.F. range. However, anR.F. stage is often added in front of a regenerative detector stageeven at L.F./M.F. This is nothing to do with "boosting" the R.F. signalbut more to do with isolating or decoupling the antenna from thedetector stage. A number of problems can arise when the antenna istightly coupled to the detectors tuned circuit, these problems include,detector radiation, "dead spots" within the tuning range, overloadingof the detector and mis-tuning of the detector tuned circuit by theantenna. The cure for all these effects is the addition of a lowor unity gain R.F. stage. This can be of the tuned or un-tuned varietybut I chose to use a tuned R.F. stage because the extra tuned circuitserves to improve selectivity and provides increased performance whentuning in weak signals which are very close in frequency to stronger(local) radio signals.
In rough tests on the bench it was found that a VFD R.F.stage would operate at medium wave frequencies without anyneutralization and remained stable. This is perhaps due to thelow-mu/low gain of the VFD's. However, for "peace of mind" it wasdecided that a neutralized triode circuit would be used loosely basedon the "Hazeltine-Neutrodyne" designswhich date back to the 1920's. Neutralization is often required inorder to counteract the effects of grid to anode/plate capacitancewhich exists in all valves/tubes to some extent. This grid toanode/plate capacitance can result in some of the amplified anode/platesignal being returned to the control grid. Depending on theamplitude/phase relationship of the feedback it can result ininstability or oscillation of the stage. The schematic of the RF andDetector stages of the receiver appear below.
The neutralization circuit works by feeding back a signal of the sameamplitude but 180 degrees out-of-phase with that of the signal due togrid/plate capacitance. The amplitude of the out-of-phase signal isadjusted using the "neutralizing trimmer" shown in the schematic above.When correctly set the unwanted feedback caused by the anode/platecapacitance is canceled out by the out-of-phase feedback signal atwhich point the stage is said to be "neutralized". I chose thisparticular method of neutralization because it proved to be easy toimplement and set-up.
The R.F. stage also has a negative bias Voltage of 1.5 Volts applied tothe control grid. In tests the stage worked perfectly well with orwithout the bias but with the negative bias applied the VFD'sstanding current was reduced which in turn reduced the batteryconsumption. I also felt that a little bit of negative bias wouldensure better linearity of the R.F. stage in the presence of strongsignals.
Here at M0AYF we have a very strong local signal at the higher end ofthe MW band from a transmitter located just 17 miles away so in orderto avoid overloading of the R.F. stage a variable inductive couping wasimplemented. The fixed spider coil which forms part of the tunedcircuit in the R.F. stage is coupled to a smaller rotating spider coil.This second smaller coil is able to rotate through 90 degrees and isadjusted via a front panel control. When the two coils are at rightangles to each other the coupling is at a minimum. A picture of thecoupler is shown below.
For more information on V.F.D.'s see references 1,2,3 and 6 in the "References and Links" section at the bottom of this page.
VFD's used as Valves/Vacuum Tubes.
The receiver described here follows mostly tried and trusted methods ofconstruction with one major exception, VFD's have been used in place ofvalves/vacuum tubes in order to simulate low-mu triodes and to satisfymy own curiosity regarding the use of VFD's for non displayapplications.
Single VFD tubes (sometimes described as "first generation" VFD's) salvaged from an old desk-top calculator have beenused because they seemed well suited for constructing the individualstages of the receiver on a one tube/VFD per stage basis. In each caseall the anodes/plates (seven segments plus decimal point) of thetubes/VFD's have been strapped together to form a single anode/plateconnection. In tests this arrangement seemed to give the bestperformance. Though there is some evidence of the potential gradienteffect mentioned earlier it caused no problems in practice aside from avery slight non uniformity of brilliance over the display area. Indeed,if you look at this "VFD Lit-Up"image it is hard to see any significant difference in brightnessbetween the top and bottom of the display. Using single tubes/VFD'salso permits physical separation of the individual stages of thereceiver which makes it easier to achieve good stability.
First tests using VFD's in place of triode valves/tubes did not lookvery promising. In normal display operation a VFD may have only +40Volts on its anodes/plates and in order to secure sufficient currentflow and display brightness they often resort to some positive Voltagebias applied to the control grid which in turn permits some controlgrid current to flow. This mode of operation is quite satisfactory fordisplay purposes but is not well suited for small signal amplification.
For the initial tests I used a +40 Volt DC supply for the anodes/platessince this is the Voltage which had been used in the desk-top calculatorfrom which the VFD's had been salvaged. I joined all the anodes/platestogether to form a single anode/plate connection. A resistor in theanode was chosen to limit the current to a safe value of around 100micro amps for testing. This was about the same value of current usedfor each individual segment of the display when used in the calculatorand provided a bright display.
With +40 Volts on the anodes I could not get the VFD's to workcorrectly as a small signal amplifier. Indeed, with the control gridconnected to zero Volts via a one mega-Ohm resistor little or nocurrent would flow from the filament to the anodes/plates. Increasingthe anode/plate Voltage to +120 Volts improved matters and I could now see somesigns of current flow (glowing anodes/plates) and signs ofamplification. Finally I increased the HT supply to +200 Volts (andalso increased the value of the anode load resistor) at which point theVFD device began behaving much like a valve/vacuum tube.
Receiver Description.
Thereceiver is a "regenerative" type or (if you prefer) "straight"setwith some controlled positive feedback applied to enhance theselectivityand sensitivity. This type of receiver was very popular in the 1930'sand still finds favour today among radio enthusiasts. Since the VFD'sare in a triode format it means that all the stages of the receiverwould have to use circuitry best suited to the triode configuration. Though the gain of the individual tubes is quite low they areelectrically very "quiet" resulting in a good signal-to-noise ratio. This is also true of "real" triode valves/tubes.
The configuration chosen for the receiver is a 1-V-2 arrangement, thatis, one stage of RF amplification followed by a regenerative detectorstage and two stages of audio frequency amplification. The set-up is asfollows...
R.F. stage = single neutralized triode/VFD.
Detector stage = single triode/VFD.
First A.F. (preamplifier) stage = single triode/VFD.
Second A.F. stage = two triodes/VFD's wired in parallel.
The R.F. stage.
The use of an R.F. stage in a regenerative receiver is oftenmisunderstood. When correctly implemented the regenerative detector isexceptionally sensitive and has no need of additional R.F.amplification below frequencies in the upper H.F. range. However, anR.F. stage is often added in front of a regenerative detector stageeven at L.F./M.F. This is nothing to do with "boosting" the R.F. signalbut more to do with isolating or decoupling the antenna from thedetector stage. A number of problems can arise when the antenna istightly coupled to the detectors tuned circuit, these problems include,detector radiation, "dead spots" within the tuning range, overloadingof the detector and mis-tuning of the detector tuned circuit by theantenna. The cure for all these effects is the addition of a lowor unity gain R.F. stage. This can be of the tuned or un-tuned varietybut I chose to use a tuned R.F. stage because the extra tuned circuitserves to improve selectivity and provides increased performance whentuning in weak signals which are very close in frequency to stronger(local) radio signals.
In rough tests on the bench it was found that a VFD R.F.stage would operate at medium wave frequencies without anyneutralization and remained stable. This is perhaps due to thelow-mu/low gain of the VFD's. However, for "peace of mind" it wasdecided that a neutralized triode circuit would be used loosely basedon the "Hazeltine-Neutrodyne" designswhich date back to the 1920's. Neutralization is often required inorder to counteract the effects of grid to anode/plate capacitancewhich exists in all valves/tubes to some extent. This grid toanode/plate capacitance can result in some of the amplified anode/platesignal being returned to the control grid. Depending on theamplitude/phase relationship of the feedback it can result ininstability or oscillation of the stage. The schematic of the RF andDetector stages of the receiver appear below.
The neutralization circuit works by feeding back a signal of the sameamplitude but 180 degrees out-of-phase with that of the signal due togrid/plate capacitance. The amplitude of the out-of-phase signal isadjusted using the "neutralizing trimmer" shown in the schematic above.When correctly set the unwanted feedback caused by the anode/platecapacitance is canceled out by the out-of-phase feedback signal atwhich point the stage is said to be "neutralized". I chose thisparticular method of neutralization because it proved to be easy toimplement and set-up.
The R.F. stage also has a negative bias Voltage of 1.5 Volts applied tothe control grid. In tests the stage worked perfectly well with orwithout the bias but with the negative bias applied the VFD'sstanding current was reduced which in turn reduced the batteryconsumption. I also felt that a little bit of negative bias wouldensure better linearity of the R.F. stage in the presence of strongsignals.
Here at M0AYF we have a very strong local signal at the higher end ofthe MW band from a transmitter located just 17 miles away so in orderto avoid overloading of the R.F. stage a variable inductive couping wasimplemented. The fixed spider coil which forms part of the tunedcircuit in the R.F. stage is coupled to a smaller rotating spider coil.This second smaller coil is able to rotate through 90 degrees and isadjusted via a front panel control. When the two coils are at rightangles to each other the coupling is at a minimum. A picture of thecoupler is shown below.
Regen Detector Stage.
Theregenerative detector stage is fairly conventional and is of the "gridleak detector" variety incorporating positive feedback from theanode/plate via inductive coupling using a "tickler" coil. Because thereceiver tunes over the entire MW band (plus a little extra) it wasdecided that both a "coarse" and "fine" regen (feedback) control wouldbe fitted. When tuning over a wide range of frequencies using a regencircuit it is often found that the regen (positive feedback) tends tofall-off or reduce as the frequency gets lower. While it is possible tomake a regen control with sufficient "scope" to work correctly over thefull band it is often found that the control becomes very "coarse" inoperation making the receiver difficult to use. Smoother control of theregen results if the operation of the control is s-p-r-e-a-d out. Thiscan be done using two controls for regen, one coarse and one fine.
The coarse regen is implemented using another variable inductancecoupling, unlike the R.F. stage antenna coupler the coarse regencoupler has both the detector stage tuned coil and the feedback(tickler) coil in-line with each other. Control of the tickler couplingis achieved using a rotating axle (plastic knitting needle) upon whichthe tickler coil is mounted. The axle has 90 degrees of rotation and iscoupled to a front panel control. The rotating axle also passes throughthe detector coil but since the detector coil is not fixed to the axleit does not move. Fine control of the regen is implemented using avariable capacitor connected from one end of the tickler coil to groundas a "throttle" control arrangement. Some pictures of the mechanicalarrangements can be seen below.
Theregenerative detector stage is fairly conventional and is of the "gridleak detector" variety incorporating positive feedback from theanode/plate via inductive coupling using a "tickler" coil. Because thereceiver tunes over the entire MW band (plus a little extra) it wasdecided that both a "coarse" and "fine" regen (feedback) control wouldbe fitted. When tuning over a wide range of frequencies using a regencircuit it is often found that the regen (positive feedback) tends tofall-off or reduce as the frequency gets lower. While it is possible tomake a regen control with sufficient "scope" to work correctly over thefull band it is often found that the control becomes very "coarse" inoperation making the receiver difficult to use. Smoother control of theregen results if the operation of the control is s-p-r-e-a-d out. Thiscan be done using two controls for regen, one coarse and one fine.
The coarse regen is implemented using another variable inductancecoupling, unlike the R.F. stage antenna coupler the coarse regencoupler has both the detector stage tuned coil and the feedback(tickler) coil in-line with each other. Control of the tickler couplingis achieved using a rotating axle (plastic knitting needle) upon whichthe tickler coil is mounted. The axle has 90 degrees of rotation and iscoupled to a front panel control. The rotating axle also passes throughthe detector coil but since the detector coil is not fixed to the axleit does not move. Fine control of the regen is implemented using avariable capacitor connected from one end of the tickler coil to groundas a "throttle" control arrangement. Some pictures of the mechanicalarrangements can be seen below.
AF Stages.
The A.F. stages of the receiver need little explanation except to saythat three tubes have been used in order to give "rockcrushing" volume with reasonably low distortion into a pair of lowimpedance personal stereo headphones. The use of two tubes in parallelfor the headphone output stage was to give added "peace of mind" as itwas thought that a single tube might be "stressed" a little.Theoretically the two tubes (when connected in parallel) should beclosely matched but in practice I selected two tubes at random andfound the current spit between the two tubes was pretty evenlydistributed. The same 1.5 Volt negative bias supply used for the R.F.stage is also used for the output stage in order to move the operatingpoint of the VFD's to secure a more linear (lower distortion) regionand thus reduce distortion on loud signals. A schematic of the A.F.stages appears here.
Power Supply.
Thereceiver requires three separate power supplies, a 1.5 Volt filamentsupply at around 300 mA, a 1.5 Volt negative grid bias bias supply and a H.T. supply ofbetween 150 and 200 Volts at around 1 mA. All three supplies are derived from drybatteries. Though less convenient than a mains powered unit they offerthe advantage of a truly "silent" background when tuning betweenstations, no "hum" or "buzz" from power supply transformer magnetic fields or powersupply harmonics etc.
Both the negative grid bias supply and the filament supply use a1.5 Volt alkaline cell. Alkaline cells have a very long shelf lifewhich makes them ideal for the grid bias supply. The grid bias supplydraws virtually zero current regardless of the radio being switched onor off so the cell will last for perhaps years. I used a "run down"cell for the negative bias supply since the internal resistance of thecell makes little difference in this application and because it helps to recycle an old cell.
An alkaline cell is also used for the filament supply, all five VFDtubes have the filaments connected together in parallel so a singlecell runs all five tubes. Wires have been soldered to the terminals ofthe cell such that it could be mounted in a cardboard box with externalscrew terminals fitted. This is a re-usable box which permits a newcell to be fitted when the old one is exhausted.
TheH.T. supply (up to 200 Volts) is derived from a total of twenty 9 Volttransistor radio batteries. Two H.T. battery boxes house the batteries(ten in each box) and are connected in series to give a nominal +180Volts. In practice the Voltage isgreater than +200 Volts when the batteries are new. This ispotentially dangerous so please exercise caution if you choose toreplicate any of the experiments outlined on this page. Becauseof the relatively low consumption of the receiver (about one milliamp) and only intermittentuse the batteries will last for a very long time. A couple of pictures ofthe battery boxes appear below.
The A.F. stages of the receiver need little explanation except to saythat three tubes have been used in order to give "rockcrushing" volume with reasonably low distortion into a pair of lowimpedance personal stereo headphones. The use of two tubes in parallelfor the headphone output stage was to give added "peace of mind" as itwas thought that a single tube might be "stressed" a little.Theoretically the two tubes (when connected in parallel) should beclosely matched but in practice I selected two tubes at random andfound the current spit between the two tubes was pretty evenlydistributed. The same 1.5 Volt negative bias supply used for the R.F.stage is also used for the output stage in order to move the operatingpoint of the VFD's to secure a more linear (lower distortion) regionand thus reduce distortion on loud signals. A schematic of the A.F.stages appears here.
Power Supply.
Thereceiver requires three separate power supplies, a 1.5 Volt filamentsupply at around 300 mA, a 1.5 Volt negative grid bias bias supply and a H.T. supply ofbetween 150 and 200 Volts at around 1 mA. All three supplies are derived from drybatteries. Though less convenient than a mains powered unit they offerthe advantage of a truly "silent" background when tuning betweenstations, no "hum" or "buzz" from power supply transformer magnetic fields or powersupply harmonics etc.
Both the negative grid bias supply and the filament supply use a1.5 Volt alkaline cell. Alkaline cells have a very long shelf lifewhich makes them ideal for the grid bias supply. The grid bias supplydraws virtually zero current regardless of the radio being switched onor off so the cell will last for perhaps years. I used a "run down"cell for the negative bias supply since the internal resistance of thecell makes little difference in this application and because it helps to recycle an old cell.
An alkaline cell is also used for the filament supply, all five VFDtubes have the filaments connected together in parallel so a singlecell runs all five tubes. Wires have been soldered to the terminals ofthe cell such that it could be mounted in a cardboard box with externalscrew terminals fitted. This is a re-usable box which permits a newcell to be fitted when the old one is exhausted.
TheH.T. supply (up to 200 Volts) is derived from a total of twenty 9 Volttransistor radio batteries. Two H.T. battery boxes house the batteries(ten in each box) and are connected in series to give a nominal +180Volts. In practice the Voltage isgreater than +200 Volts when the batteries are new. This ispotentially dangerous so please exercise caution if you choose toreplicate any of the experiments outlined on this page. Becauseof the relatively low consumption of the receiver (about one milliamp) and only intermittentuse the batteries will last for a very long time. A couple of pictures ofthe battery boxes appear below.
Receiver Construction and Pictures.
The construction techniques used are intended to reflect some of themethods used for home constructed receivers back in the 1930's.These are generally low budget methods with many of the components homemade ifpossible. I stopped short of making my own resistors and capacitors,while this is possible it would have also taken much longer to buildthe receiver. I was also very impatient to see how the VFD's and"spider"coils performed in the finished radio. Some more information andtemplates for making spider coils can be found in references 11, 12, 13and 14 in the "References and Links" section at the bottom of this page. A close-up picture of one of thespider coils appears below.
Thematerials used include a varnished wood baseboard to serve as a chassisand an enclosure made from scrap hardboard which was painted mat black.The individual stages of the receiver are constructed on tin lidssalvaged from food cans. They made effective supports for thewire-ended VFD devices and also provided a local "ground plane" area.Interconnection between the different stages is via insulated wires.The "tin lid" construction can be seen in the images below.
Test Results.
The "Retro-Regen" was tested using a home-brew Wide Bandwidth Active Loop Receiving Antenna andperformed much better than expected. It easily matches or (in somecases) exceeds the performance of an old Cossor model 393 regenreceiver which was manufactured in the late 1930's and used here asa reference with which to compare the retro regen's performance.
While the retro regen is not capable of driving a loudspeaker directlyit more than makes up for this in other respects. The receiver is freeof "reaction chasing" (or regen chasing), this is an annoying problemwhich sometimes plagues regen receivers. The symptoms of reaction/regenchasing are a difficulty in securing the optimum tuning point as theregen control is advanced (more positive feedback) such that as theoperator advances the regen the main tuning also has to be re-adjusted.This in turn causes the optimum regen point to shift so it to must bere-adjusted. This interaction or "chasing" between the two controlscontinues and gets worse as the regen is advanced. The cause ofreaction chasing is often due to over coupling of the "tickler" coil tothe detectors tuned circuit such that changing reactance in thefeedback circuit is coupled to the detector tuned circuit and "pulls"the tuning a little. Thankfully, the retro regen behaves well with noevidence of reaction pulling. Some MP3 clips of the retro-regen in action can be found in the "MP3 Audio Clips" section of this web page.
The receivers sensitivity is very good and weaker stations can bepulled from the forest of stronger EU stations quite easily. There issome loss of sensitivity at the L.F. end of the MW band due I suspectto the reduced coupling between the R.F. and Detector stages as the frequency gets lower. Withinthe limitations of the regenerative detector the receiver copes fairlywell with strong signals, in the event of a strong local signals-p-r-e-a-d-i-n-g over the band the antenna coupling can be reducedwhich usually cures the problem. One unexpected result of the receivershigh sensitivity is its ability to receive signals with no antennaconnected, at first this was thought to be due to pick-up in the wiringbut further tests revealed that the home made spider coils behaved assmall frame antennas. Had the receiver been housed in a steel box thiswould not happen.
Though the gain of the individual tubes is quite low they areelectrically very "quiet" resulting in a good signal-to-noise ratio. This is also true of "real" triode valves to.In common with regular battery valves (1T4 andsimilar) the VFD's are "microphonic" to some extent so if they aretapped with apencil while powered-up a "ping" can be heard in the headphones.Thankfully the wire ended connections of the VFD's act as shockabsorbers to some extent and reduce the effects of vibration from thecase and its surroundings. This microphonic effect is mainly due to thefilament and internal electrode structure of the VFD mechanicallyvibrating. The effect becomes more problematic with an increasingnumber of cascaded audio stages. The Retro-Regen has three cascadedaudio stages, the detector (which also amplifies at A.F.) followed byan A.F. pre-amplifier stage and finally the A.F. headphone outputstage. Since the detector is the first of these cascaded A.F. stages itis also the most microphonic. You can hear the "ping" sound made by thedetector stage VFD tube being "tapped" by downloading and playingthe MP3 audio clip (number 8) in the "MP3 Audio Clips"section of this web page. Another VFD experimenter has made full use ofthis microphonic effect in VFD tubes by building a pseudo ringmodulator, see reference 8 in the "References and Links" section at the bottom of this page.
One amusing side-effect of using VFD's for the receiver is the "visualfeedback" they provide. When the VFD's are in the "linear region" ordriven with very small signals then the "glow" is continuous. However,if the VFD's are over-driven into the non linear region then they canbe seen to "flicker", this effect is most noticeable on the A.F. outputstage VFD's on strong/loud signals. Similar visual feedback occurs withthe detector stage, as the detector is tuned through a strong signalthe brilliance of the glow can be seen to reduce slightly. This iscaused by the grid-leak detector action, as the negative Voltage buildsup on the control grid due to the strong signal it biases the VFD tubeso as to reduce the quiescent current. As the signal strength getshigher so to does the negative bias and hence a greater reduction inbrilliance of the VFD. This reduction in brilliance of the VFD detectortube can also be seen as the detector is taken into oscillation.
Final Comments.
Thisreceiver turned out to be a very rewarding and educational project, Idiscovered several new things about regen circuits and VFD's whichhave inspired several new projects. These include a VFD transmitter, aVFD 40 Mtr amateur band crystal controlled converter andseveral other VFD regen designs. These additional projects are (atthe timeof writing) still undergoing tests on the work bench but may (in time)find themselves on a web page. Of those projects listed above thefrequency converter has given very encouraging results. Whenconnected in front of the retro-regen it permits reception of the 40Mtr amateur band. Reception of AM/CW and SSB are all possible. MP3audio clips 1 and 2 in the "MP3 Audio Clips" section of this web page demonstrate SSB reception achieved using the 40 Mtr VFD converter ahead of the retro-regen.
For anyone considering building a project using VFD's salvaged fromVCR's or calculators etc then please make sure that the VFD's are fullyoperational before you start. Old VCR displays in particular aresometimes lacking in brilliance. This lack of brilliance may be theresult of long hours of service resulting in damaged or burnt phosphorsor the result of failing emission from the cathode/filament. If thelack of brilliance is due to worn phosphors then the emission may stillbe good enough for VFD radio experiments but if the loss of brillianceis due to failing emission then this may pose a problem for prospectiveVFD radio use. So, look for a surplus or scrap item which still has aworking VFD with a bright display.
A number of other radio hams and experimenters have also used VFD's inother applications, see references 4, 5, 6, 7, 8 and 9 in the "References and Links" section at the bottom of this page.
Finally, if after reading this you decide to build any projects usingVFD's or if you have already built a radio project using VFD's thenplease drop me a line, I would be interested to hear about yourexperiments.
The construction techniques used are intended to reflect some of themethods used for home constructed receivers back in the 1930's.These are generally low budget methods with many of the components homemade ifpossible. I stopped short of making my own resistors and capacitors,while this is possible it would have also taken much longer to buildthe receiver. I was also very impatient to see how the VFD's and"spider"coils performed in the finished radio. Some more information andtemplates for making spider coils can be found in references 11, 12, 13and 14 in the "References and Links" section at the bottom of this page. A close-up picture of one of thespider coils appears below.
Test Results.
The "Retro-Regen" was tested using a home-brew Wide Bandwidth Active Loop Receiving Antenna andperformed much better than expected. It easily matches or (in somecases) exceeds the performance of an old Cossor model 393 regenreceiver which was manufactured in the late 1930's and used here asa reference with which to compare the retro regen's performance.
While the retro regen is not capable of driving a loudspeaker directlyit more than makes up for this in other respects. The receiver is freeof "reaction chasing" (or regen chasing), this is an annoying problemwhich sometimes plagues regen receivers. The symptoms of reaction/regenchasing are a difficulty in securing the optimum tuning point as theregen control is advanced (more positive feedback) such that as theoperator advances the regen the main tuning also has to be re-adjusted.This in turn causes the optimum regen point to shift so it to must bere-adjusted. This interaction or "chasing" between the two controlscontinues and gets worse as the regen is advanced. The cause ofreaction chasing is often due to over coupling of the "tickler" coil tothe detectors tuned circuit such that changing reactance in thefeedback circuit is coupled to the detector tuned circuit and "pulls"the tuning a little. Thankfully, the retro regen behaves well with noevidence of reaction pulling. Some MP3 clips of the retro-regen in action can be found in the "MP3 Audio Clips" section of this web page.
The receivers sensitivity is very good and weaker stations can bepulled from the forest of stronger EU stations quite easily. There issome loss of sensitivity at the L.F. end of the MW band due I suspectto the reduced coupling between the R.F. and Detector stages as the frequency gets lower. Withinthe limitations of the regenerative detector the receiver copes fairlywell with strong signals, in the event of a strong local signals-p-r-e-a-d-i-n-g over the band the antenna coupling can be reducedwhich usually cures the problem. One unexpected result of the receivershigh sensitivity is its ability to receive signals with no antennaconnected, at first this was thought to be due to pick-up in the wiringbut further tests revealed that the home made spider coils behaved assmall frame antennas. Had the receiver been housed in a steel box thiswould not happen.
Though the gain of the individual tubes is quite low they areelectrically very "quiet" resulting in a good signal-to-noise ratio. This is also true of "real" triode valves to.In common with regular battery valves (1T4 andsimilar) the VFD's are "microphonic" to some extent so if they aretapped with apencil while powered-up a "ping" can be heard in the headphones.Thankfully the wire ended connections of the VFD's act as shockabsorbers to some extent and reduce the effects of vibration from thecase and its surroundings. This microphonic effect is mainly due to thefilament and internal electrode structure of the VFD mechanicallyvibrating. The effect becomes more problematic with an increasingnumber of cascaded audio stages. The Retro-Regen has three cascadedaudio stages, the detector (which also amplifies at A.F.) followed byan A.F. pre-amplifier stage and finally the A.F. headphone outputstage. Since the detector is the first of these cascaded A.F. stages itis also the most microphonic. You can hear the "ping" sound made by thedetector stage VFD tube being "tapped" by downloading and playingthe MP3 audio clip (number 8) in the "MP3 Audio Clips"section of this web page. Another VFD experimenter has made full use ofthis microphonic effect in VFD tubes by building a pseudo ringmodulator, see reference 8 in the "References and Links" section at the bottom of this page.
One amusing side-effect of using VFD's for the receiver is the "visualfeedback" they provide. When the VFD's are in the "linear region" ordriven with very small signals then the "glow" is continuous. However,if the VFD's are over-driven into the non linear region then they canbe seen to "flicker", this effect is most noticeable on the A.F. outputstage VFD's on strong/loud signals. Similar visual feedback occurs withthe detector stage, as the detector is tuned through a strong signalthe brilliance of the glow can be seen to reduce slightly. This iscaused by the grid-leak detector action, as the negative Voltage buildsup on the control grid due to the strong signal it biases the VFD tubeso as to reduce the quiescent current. As the signal strength getshigher so to does the negative bias and hence a greater reduction inbrilliance of the VFD. This reduction in brilliance of the VFD detectortube can also be seen as the detector is taken into oscillation.
Final Comments.
Thisreceiver turned out to be a very rewarding and educational project, Idiscovered several new things about regen circuits and VFD's whichhave inspired several new projects. These include a VFD transmitter, aVFD 40 Mtr amateur band crystal controlled converter andseveral other VFD regen designs. These additional projects are (atthe timeof writing) still undergoing tests on the work bench but may (in time)find themselves on a web page. Of those projects listed above thefrequency converter has given very encouraging results. Whenconnected in front of the retro-regen it permits reception of the 40Mtr amateur band. Reception of AM/CW and SSB are all possible. MP3audio clips 1 and 2 in the "MP3 Audio Clips" section of this web page demonstrate SSB reception achieved using the 40 Mtr VFD converter ahead of the retro-regen.
For anyone considering building a project using VFD's salvaged fromVCR's or calculators etc then please make sure that the VFD's are fullyoperational before you start. Old VCR displays in particular aresometimes lacking in brilliance. This lack of brilliance may be theresult of long hours of service resulting in damaged or burnt phosphorsor the result of failing emission from the cathode/filament. If thelack of brilliance is due to worn phosphors then the emission may stillbe good enough for VFD radio experiments but if the loss of brillianceis due to failing emission then this may pose a problem for prospectiveVFD radio use. So, look for a surplus or scrap item which still has aworking VFD with a bright display.
A number of other radio hams and experimenters have also used VFD's inother applications, see references 4, 5, 6, 7, 8 and 9 in the "References and Links" section at the bottom of this page.
Finally, if after reading this you decide to build any projects usingVFD's or if you have already built a radio project using VFD's thenplease drop me a line, I would be interested to hear about yourexperiments.
Well, that's about it, thank you for reading this and pleasesend any questions, comments or "heckles" etc to the e-mail address linked below.
Des (M0AYF)
| XE1GXG | 2009-02-11 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| Great article, well written and highly engaging..even if I don't build the RCVR. | ||
| K1IO | 2009-02-09 | |
|---|---|---|
| Lemony good | ||
| This is absolutely insane. You have to be off your rocker to do this. I love it! When I see the term "VFD", I'm reminded of Lemony Snicket's "A Series of Unfortunate Events" books, which feature the search for a shadowy organization known only by its initials "VFD". Sort of fitting. | ||
| W8ZNX | 2009-01-25 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| sure nice but sry om but im not going to play with triode autodynes there are tons of nos cheap cheap screen grid tubes to use nice try keep up the good work but using the wrong tool for a job just because its handy and glows in the dark does not quite get it dit dit mac Reply to a comment by : N9CYS on 2009-01-23 Terrific article!! Reminds me of the circuits I first studied as a Novice a looooooong time ago. If you look closely at these schematics, you can understand CORE receiver functions and understand how primary electronic components function. Bravo! Jim N9CYS | ||
| N9CYS | 2009-01-23 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| Terrific article!! Reminds me of the circuits I first studied as a Novice a looooooong time ago. If you look closely at these schematics, you can understand CORE receiver functions and understand how primary electronic components function. Bravo! Jim N9CYS | ||
| K4IQT | 2009-01-23 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| Thanks for the idea, Des. I've got an old VFD calculator laying around, still working but not worth a dollar at any flea market, and too good to throw away. I used to build my TX's and RX's and everything else from salvaged TV's, so it makes perfect sense to recycle this calculator too. Again, thanks for the informative and innovative writeup! | ||
| K5END | 2009-01-23 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| Outstanding article! It's perhaps the most original and well-penned electronics piece I've seen, in any venue. This article is award-level material. ************************************** I took K0BG's comment at face value and had already started planning my 160 m QRP/Ti-Calc rig. Coincidentally I had to rescue the box of appointed calculators from the trash ("rubbish," for you folks across the pond) this morning. XYL rev. 2.0 had been doing some house cleaning and had sentenced these innocent gadgets to the landfill. That is just so, so wrong, on so many levels. :-) Reply to a comment by : WR9H on 2009-01-23 You sir, are an artist!! My goal is to be half the designer and builder that you are. Thanks for the very cool post!! Herb WR9H | ||
| WR9H | 2009-01-23 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| You sir, are an artist!! My goal is to be half the designer and builder that you are. Thanks for the very cool post!! Herb WR9H | ||
| M0AYF | 2009-01-23 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| Hi again, Just a few lines to say "thanks" for all the positive comment and support received so far relating to the "Triodes in Disguise" article. Many thanks es 73,s Des (M0AYF author of "Triodes in Disguise") Reply to a comment by : M0AYF on 2009-01-23 Hi there, Tom (WB6DGN) wrote: I thought VFD referred to "vacuum fluorescent display". I've never heard the term "voltage fluorescent display". Can someone please clarify? ***** Thankyou, yes thats one "massive" typo on my part, worse still its in the title :-( I spent ages going through the text and still managed to miss that one. It should of course read "Vacuum Fluorescent Display" and not "voltage fluorescent display", sorry for the confussion. I will correct the error on the RSGB web-page in due course, thanks again for pointing it out. 73,s Des (M0AYF the author of "Triodes in Disguise") Reply to a comment by : WB6DGN on 2009-01-22 At the risk of being called a nit picker (I've been called a lot worse) I thought VFD referred to "vacuum fluorescent display". I've never heard the term "voltage fluorescent display". Can someone please clarify? Tom | ||
| M0AYF | 2009-01-23 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| Hi there, Tom (WB6DGN) wrote: I thought VFD referred to "vacuum fluorescent display". I've never heard the term "voltage fluorescent display". Can someone please clarify? ***** Thankyou, yes thats one "massive" typo on my part, worse still its in the title :-( I spent ages going through the text and still managed to miss that one. It should of course read "Vacuum Fluorescent Display" and not "voltage fluorescent display", sorry for the confussion. I will correct the error on the RSGB web-page in due course, thanks again for pointing it out. 73,s Des (M0AYF the author of "Triodes in Disguise") Reply to a comment by : WB6DGN on 2009-01-22 At the risk of being called a nit picker (I've been called a lot worse) I thought VFD referred to "vacuum fluorescent display". I've never heard the term "voltage fluorescent display". Can someone please clarify? Tom | ||
| WB6DGN | 2009-01-22 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| "Twenty 9 volt batteries are easier to find than a pair of functioning "B" batteries." I know! I've got a nice portable radio from when I was a kid...say, you've just given me a great idea! Now, if I can just come up with a container about the right size and shape! And, it won't leak like those old carbon/zinc things did! Tom Reply to a comment by : NB3O on 2009-01-22 Twenty 9 volt batteries are easier to find than a pair of functioning "B" batteries. Reply to a comment by : K4RAF on 2009-01-22 "a total of twenty 9 Volt transistor radio batteries..." Huh? Absurd... Reply to a comment by : KL7AJ on 2009-01-22 Very Very nice. I have a 6E5 magic eye tube wondering what it should do with itself. :) By the way..the SPIDER coils are very cool. Lotsa folk don't know the whys and wherefores for them. The spider winding is to reduce interwinding capacitance. If constructed well, the wires are never parallel to each other, but cross at nearly right angles. It seems like a pain in the posterior to do it that way, but this really truly and genuinely did huge things for the overall performance and Q. Eric | ||
| WB6DGN | 2009-01-22 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| At the risk of being called a nit picker (I've been called a lot worse) I thought VFD referred to "vacuum fluorescent display". I've never heard the term "voltage fluorescent display". Can someone please clarify? Tom | ||
| AC7CW | 2009-01-22 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| Amateur radio is a HOBBY!! [excuse the yelling please :)]. Desultory comments here and there ruin it, momentarily at least, for those who HAVE FUN AT THEIR HOBBY [again, apologies, hope everybody's ears are still ok !(--)!]. Again, I really enjoyed the article and kudos on the basic design. Putting the RF stage in there to decouple the antenna from the mixer is sweet, paralleling the audio elements.. well it's good info you can do that and it doesn't get unbalanced in the current draw... I think maybe the author gets a lot of enjoyment out of just doing something right maybe. Doing something really well is efficiency, doing the right things is effectiveness.... but, it's a hobby, who cares about effective? Effective is for guys that buy a box they can barely operate, let alone design and build... go on, buy your boxes, work a zillion countries... show us all how effective you are.. I'll put my endorphin level up against yours anytime!! Max Reply to a comment by : NB3O on 2009-01-22 Twenty 9 volt batteries are easier to find than a pair of functioning "B" batteries. Reply to a comment by : K4RAF on 2009-01-22 "a total of twenty 9 Volt transistor radio batteries..." Huh? Absurd... Reply to a comment by : KL7AJ on 2009-01-22 Very Very nice. I have a 6E5 magic eye tube wondering what it should do with itself. :) By the way..the SPIDER coils are very cool. Lotsa folk don't know the whys and wherefores for them. The spider winding is to reduce interwinding capacitance. If constructed well, the wires are never parallel to each other, but cross at nearly right angles. It seems like a pain in the posterior to do it that way, but this really truly and genuinely did huge things for the overall performance and Q. Eric | ||
| NB3O | 2009-01-22 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| Twenty 9 volt batteries are easier to find than a pair of functioning "B" batteries. Reply to a comment by : K4RAF on 2009-01-22 "a total of twenty 9 Volt transistor radio batteries..." Huh? Absurd... Reply to a comment by : KL7AJ on 2009-01-22 Very Very nice. I have a 6E5 magic eye tube wondering what it should do with itself. :) By the way..the SPIDER coils are very cool. Lotsa folk don't know the whys and wherefores for them. The spider winding is to reduce interwinding capacitance. If constructed well, the wires are never parallel to each other, but cross at nearly right angles. It seems like a pain in the posterior to do it that way, but this really truly and genuinely did huge things for the overall performance and Q. Eric | ||
| K4RAF | 2009-01-22 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| "a total of twenty 9 Volt transistor radio batteries..." Huh? Absurd... Reply to a comment by : KL7AJ on 2009-01-22 Very Very nice. I have a 6E5 magic eye tube wondering what it should do with itself. :) By the way..the SPIDER coils are very cool. Lotsa folk don't know the whys and wherefores for them. The spider winding is to reduce interwinding capacitance. If constructed well, the wires are never parallel to each other, but cross at nearly right angles. It seems like a pain in the posterior to do it that way, but this really truly and genuinely did huge things for the overall performance and Q. Eric | ||
| W8AAZ | 2009-01-22 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| I have just recently finished a pretty faithful replica of a "Twinplex" shortwave regen using all old parts as much as possible. This design uses the early number 19 dual triode. Two direct heated triodes in an ST glass envelope and a 6 pin base. The regen. control needs constant attention while tuning but the performance is quite stunning to somene who has been using superhets exclusively for SW reception. I have plenty of regen. antique BC band sets. The 19 dual triode is quite a bargain at around 5-5.50$ as NOS. The competing configuration at the time(ca. 1934) was two number 30 triodes. Those are quite alot more expensive for some reason. This set using plug-in band coils, gives quite amazing performance for a single envelope dual triode. Detector and audio. Strong SW stations are quite loud in any sort of hi impedance antique phones, and on loud stations it will sometimes drive my 1925 horn loudspeaker to good audible levels. I too string 9 volt batteries in series to obtain the 90 Volts required, although current drain with the set is less than 2 mA. from it. Care should be taken. I once clipped 9 volt batteries in series on a wooden workbench at work for fun. Had quite a few and the potential was probably great, how many of those batteries can be fitted onto a 5 foot bench in series? Clipped a lead to one end and was able to draw some rather impressive big bright arcs off the other end of the stack! | ||
| KL7AJ | 2009-01-22 | |
|---|---|---|
| A VFD Receiver (Triodes in Disguise) | ||
| Very Very nice. I have a 6E5 magic eye tube wondering what it should do with itself. :) By the way..the SPIDER coils are very cool. Lotsa folk don't know the whys and wherefores for them. The spider winding is to reduce interwinding capacitance. If constructed well, the wires are never parallel to each other, but cross at nearly right angles. It seems like a pain in the posterior to do it that way, but this really truly and genuinely did huge things for the overall performance and Q. Eric | ||
| K7LRB | 2009-01-22 | |
|---|---|---|
| RE: A VFD Receiver (Triodes in Disguise) | ||
| "Some people have way too much time on their hands!" I too understood exactly what you meant Alan and did not find it offensive AT ALL. Man, some of you people really need to loosen up! Have fun with ham radio and 73, de Larry Reply to a comment by : GW0DIV on 2009-01-22 I understood what you meant Allan - OMG you must be aquiring a British sense of humour!! It'll be all Monty python, John Cleese and Ricky Gervaise before you know it!!! Rhys GW0DIV Reply to a comment by : K0BG on 2009-01-22 I think a few folks took what I wrote as destructive criticism, and that isn't (wasn't) the case at all. If you have the time for such projects, you certainly do learn from them. The point being, it does take a lot of time to go through the iterations. If there is any criticism to be handed out, it is toward those who don't attempt to do any bench work, even simple, basic repair. They use the excuse that they DON'T have time on their hands. That's not me, and apparently not the author either. Alan, KØBG www.k0bg.com Reply to a comment by : WMCO on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already....THINKS he.... knows everything, there's not much left to do but pontificate. There I fixed it for ye. J.C. Reply to a comment by : K8QV on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already knows everything, there's not much left to do but pontificate. Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| GW0DIV | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| I understood what you meant Allan - OMG you must be aquiring a British sense of humour!! It'll be all Monty python, John Cleese and Ricky Gervaise before you know it!!! Rhys GW0DIV Reply to a comment by : K0BG on 2009-01-22 I think a few folks took what I wrote as destructive criticism, and that isn't (wasn't) the case at all. If you have the time for such projects, you certainly do learn from them. The point being, it does take a lot of time to go through the iterations. If there is any criticism to be handed out, it is toward those who don't attempt to do any bench work, even simple, basic repair. They use the excuse that they DON'T have time on their hands. That's not me, and apparently not the author either. Alan, KØBG www.k0bg.com Reply to a comment by : WMCO on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already....THINKS he.... knows everything, there's not much left to do but pontificate. There I fixed it for ye. J.C. Reply to a comment by : K8QV on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already knows everything, there's not much left to do but pontificate. Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| K0BG | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| I think a few folks took what I wrote as destructive criticism, and that isn't (wasn't) the case at all. If you have the time for such projects, you certainly do learn from them. The point being, it does take a lot of time to go through the iterations. If there is any criticism to be handed out, it is toward those who don't attempt to do any bench work, even simple, basic repair. They use the excuse that they DON'T have time on their hands. That's not me, and apparently not the author either. Alan, KØBG www.k0bg.com Reply to a comment by : WMCO on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already....THINKS he.... knows everything, there's not much left to do but pontificate. There I fixed it for ye. J.C. Reply to a comment by : K8QV on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already knows everything, there's not much left to do but pontificate. Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| WMCO | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already....THINKS he.... knows everything, there's not much left to do but pontificate. There I fixed it for ye. J.C. Reply to a comment by : K8QV on 2009-01-22 "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already knows everything, there's not much left to do but pontificate. Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| K8QV | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| "Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com" Experimenting, learning, doing something in the hobby. That's what it's all about. Of course, when one already knows everything, there's not much left to do but pontificate. Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| WI7B | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
Great insight, innovative thinking, and no doubt a lot of sweat. 73, ---* Ken Reply to a comment by : KT8K on 2009-01-22 This is great - in some ways similar to AA1TJ's creation of a working 40m transmitter using the parts from inside a compact flourescent light bulb. Nice job. Thanks & 73 de kt8k - Tim Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| KT8K | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| This is great - in some ways similar to AA1TJ's creation of a working 40m transmitter using the parts from inside a compact flourescent light bulb. Nice job. Thanks & 73 de kt8k - Tim Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| K1CJS | 2009-01-22 | |
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| A VFD Receiver (Triodes in Disguise) | ||
| Just one question-- Would this be considered a 'light' receiver? Sorry--couldn't resist that one! ;-) Seriously though, nice construction article. How about some more details on this project. | ||
| K6AER | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| Great artical. It;s to bad QST doesn't have articals like this. Can't wait to see their next installment on how to build a "J" pole. Reply to a comment by : ARRLBOOSTER on 2009-01-22 Fantastic article...I am glad you have time and imagination and knowledge "on your hands". Poor Alan has only time on his hands...time and cynicism that is.... Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| ARRLBOOSTER | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| Fantastic article...I am glad you have time and imagination and knowledge "on your hands". Poor Alan has only time on his hands...time and cynicism that is.... Reply to a comment by : K0BG on 2009-01-22 Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| K0BG | 2009-01-22 | |
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| RE: A VFD Receiver (Triodes in Disguise) | ||
| Some people have way too much time on their hands! The next project you should tackle is to use a bunch of the displays to build a QRP transmitter. Just imagine the jaw dropping when you tell folks your equipment is salvaged from old calculators! Alan, KØBG www.k0bg.com Reply to a comment by : M0AFJ on 2009-01-22 Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| K8QV | 2009-01-22 | |
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| A VFD Receiver (Triodes in Disguise) | ||
| That was an outstanding article. Thanks. | ||
| M0AFJ | 2009-01-22 | |
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| A VFD Receiver (Triodes in Disguise) | ||
| Well done Des, an outstanding piece of work, best I've seen on here for a long time | ||
| AC7CW | 2009-01-22 | |
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| A VFD Receiver (Triodes in Disguise) | ||
| I cut my teeth on a regen receiver, a US Navy RAL-5.. I had no idea that SSB could be pulled in!! That looks like a very enjoyable project to build and you get visual feedback from the tubes, too cool :) | ||
| N4CQR | 2009-01-22 | |
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| A VFD Receiver (Triodes in Disguise) | ||
| Outstanding piece | ||
