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eHam Forums => Boat Anchors => Topic started by: KX4QP on January 26, 2019, 12:11:24 PM



Title: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 26, 2019, 12:11:24 PM
I'm planning to build my own vacuum tube (valve, for the British speakers) receiver and VFO or VXO transmitter for CW (40 and 80 m, primarily, possibly 20 m).  Something has occurred to me -- without a frequency counter, how would one tune a particular frequency?  If answering a CQ, one "just" has to spot the TX to the RX setting and zero beat, the exact number doesn't matter (much -- need to be sure you're in a permitted band, of course), and the same is generally true when making a random CQ -- but if you're meeting a scheduled QSO, how do you be sure you're transmitting (and receiving!) on the correct frequency with boat-anchor equipment?

Operators certainly were able to do this, even with mobile equipment, during WWII and earlier (some aircraft had radios before the War, and had to tune to tower frequencies, for instance), and those certainly lacked counters at that time -- and had some tuning ability, even if they were crystal controlled.  Did the mobile operators listen for the ground station and tune to it?  Or did they just have a crystal selector and therefor a limited set of working frequencies?  Or do I have a completely wrong conception of how "call me at 0800 GMT on 7.035" worked without crystals or with tunable crystal oscillators?


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on January 26, 2019, 01:50:36 PM
Your transmitter should have a @net' position. This puts (usually) just the VFO on, and you tune it to 'zero beat' with the station you are calling. Now in CW, there's an offset equal to the CW tone you are using to set the tX VFO to the same tone, although if you don't have a single signal rx with a crystal filter, you need to be careful that you aren't a few hundred Hertz on the other side of zero beat.
 It's easier to demonstrate than to describe - finder a local old timer!


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: N8AUC on January 26, 2019, 03:21:32 PM
Back in the day when I used much older equipment, and had a home built transmitter, it went something like this...

First turn on the receiver and wait 30 minutes or so to let the VFO stabilize.
Second, turn on the crystal calibrator (usually a 100KHz crystal controlled square wave generator calibrated to WWV).
Third, set the receiver to zero beat the calibrator signal, then turn off the calibrator. Your RX dial should be pretty accurate after this step.
Fourth, tune the receiver to the desired frequency.
Fifth - disconnect (or ground) the antenna connection to your receiver to prevent damage in step 6.
Sixth, tune the transmitter frequency so you could hear your signal in the receiver.

If your transmitter had a "NET" position, or "SPOT" position, you'd turn that on to only energize the oscillator so you
could find your signal with on the receiver.

Life is much easier with modern equipment. You don't have to go through all that work anymore.
Basically, the old saying "the good old days were neither" certainly applies in this case!

73 de N8AUC
Eric


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC5UP on January 26, 2019, 04:02:01 PM
Back when stable VFO's were rare and CW was the mode of choice it wasn't uncommon to operate duplex.

Depending on local nets or other interests, the typical op would collect a series of TX crystals for multiple band segments like Novice or General as they worked their way up.  This assured they were on a known legal frequency but there was no assurance anyone else had a crystal for the same frequency.  So, they'd CQ on the crystal most likely to get a response then listen +/- 20 kHz or more.  The replying station would return the CQ for a minute or two to allow the first station to find them and once tuned they'd exchange calls, frequency, signal report, etc. along with the rest of the Q.

It should also be noted that rockbound CW wasn't foolproof as some bands were tuned on a harmonic of the fundamental crystal frequency.  This allowed a 3.5 MC crystal to double up at 7 MC with the next harmonic near 14 MC's.  This is one reason why the traditional bands are harmonically related and an opportunity for an inexperienced operator to transmit at double the intended frequency, never hearing a reply to their CQ...

 :P


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 26, 2019, 04:46:07 PM
First turn on the receiver and wait 30 minutes or so to let the VFO stabilize.
Second, turn on the crystal calibrator (usually a 100KHz crystal controlled square wave generator calibrated to WWV).
Third, set the receiver to zero beat the calibrator signal, then turn off the calibrator. Your RX dial should be pretty accurate after this step.
Fourth, tune the receiver to the desired frequency.
Fifth - disconnect (or ground) the antenna connection to your receiver to prevent damage in step 6.
Sixth, tune the transmitter frequency so you could hear your signal in the receiver.

If your transmitter had a "NET" position, or "SPOT" position, you'd turn that on to only energize the oscillator so you
could find your signal with on the receiver.

Okay, let's see here.  First, my homebrew regen receiver won't have a VFO to stabilize, though temperature effects likely will still require a warm up period to prevent it drifting after initial tuning.  There won't even be a calibrated dial on the RX, though I ought to be able to make up a log <=> frequency table by tuning known stations and noting the vernier log position (there are still a few AM broadcasts in the SW bands, and SSB operators sometimes mention their exact frequency).  I suppose I could tune WWV in the band I'm working and use that to verify my table after allowing warm up time.  BUT: I'll only be able to approximate an intended frequency (as accurately as I can read the log dial and to the limits of my conversion chart) unless I'm replying.

Also, I won't (at first) have a crystal frequency reference.  I'm starting with a soldering gun, wire cutters, etc. and a Harbor Freight multimeter, plus parts from eBay and Amazon.  Sounds like I may need to build a frequency reference alongside my transmitter project.  Might have to start prowling thrift stores for an old analog TV (colorburst crystals are all the same frequency, as I recall, and it's in our usable range -- plus, even in a modular solid state set, so long as it's a CRT type, there are other useful parts, like flybacks, capacitors, and inductors).

It does occur to me that few if any operators were able to do better than approximate before frequency counters became common equipment.  If I'm expecting a contact, I might need (as suggested in another reply) to tune a broad band around the expected frequency.  Then again, most folks I might contact will be running either digital controlled radios or VXO, so once my Morse is good enough for something beyond a basic QSO, I can probably ask for exact frequency and use that information to upgrade my frequency chart.  Duplex sounds like it was a solution to a problem that's changed into something else since.  Not that many operators are rockbound now -- most Technicians seem to operate mostly on 2 m handy-talkies.  Now that they're not forced into it, not many folks use Novice type equipment unless they just like CW or, prefer to be "retro".

Shouldn't be difficult to include a "SPOT" function when building the TX, however -- just extract the oscillator signal before it goes to the amplifier and feed it (suitably attenuated) to the RX antenna connection.  Zero beat, then retune the RX (in oscillation) to give the desired tone.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on January 27, 2019, 12:16:18 AM
In my days of using home brew TRF receivers, I built a crystal calibrator. A simple Pierce crystal oscillator and a 500kHz crystal - but you could use  almost any low frequency crystal, it's just that the harmonics won't be so conveniently spaced in frequency. If you can get a 1 or 2 MHz crystal, you can divide the frequency down with twin triode multivibrators.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 27, 2019, 04:29:31 AM
So, presuming I've built a nice, stable oscillator with a 500 kHz crystal standard, how do I select for a particular harmonic?  There will be a peak every 500 KHz until they're too weak to detect (if I build for a square wave, that'll be odd multiples up to 7x or 9x at least, though they'll be pretty faint by then).  A bandpass filter?  Frequency doublers to get into the range I need (7+ MHz)?


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: N4MQ on January 27, 2019, 05:30:17 AM
Modern days are here and can help, for less than 20$ you can buy a frequency counter that is from 1 - 500 Mc.  This could be used to monitor your transmitter rather well.

https://www.ebay.com/itm/High-Accuracy-Frequency-Counter-RF-Meter-1-500-MHz-Tester-Module-For-ham-Radiox1/332991612077?hash=item4d87d8c4ad:g:l80AAOSwAmJcLIMP:rk:1:pf:1&frcectupt=true


If you can afford some test equipment that is useful in many ways, you can get a signal generator or antenna analyzer for 100$ or less on ebay that will provide a reference signal.  I found the 55$ signal generator useful for aligning my Johnson Invader 2000, there are many very low cost items to get you going with less pain. 
 
Ebay has helped me find Johnson thunderbolt amplifiers, 6n2 THUNDERBOLTS, and the pieces needed to get them running, there is lots of ham items - like a year round ham fest.

Enjoy, Woody


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on January 27, 2019, 05:39:11 AM
Something like a 6J5 in a Pierce will give detectable harmonics up to 30 MHz with a 1 MHz or 500kHz crystal. Some sort of wavemeter is useful to determine which harmonic you have, but you can roughly determine things from what stations you can hear - the amateur bands, the BC bands (Depending where in the world you are) at 3.2 - 3.4, 3.9 - 4.0, 4.75 - 4.995, 5.005 - 5.06, 5.9 - 6.2, 7.2 - 7.45, 9.4 - 9.9, 11.6 - 12.1, 13.57 - 13.87, 15.1 - 15.8, 17.48 - 17.9, 18.9 - 19.02, 21.45 - 21.85 and 25.67 - 26.1 MHz plus the standard frequency and time signals at 2.5, 5, 10, 15 and 20 MHz, plus some other odd STFs.

An absorption wavemeter consisting a variable capacitor and an inductor in parallel will 'suck out' energy at its resonant frequency or the parallel tuned circuit in series with the antenna will trap out a signal at resonance. You can get within 5 or 10% on inductance by using the standard formula and put fixed capacitors across the coil until stations in the known band get trapped out: by using a selection of capacitors going up in double values e.g 10, 20, 40 , 80 pF etc (use nearest standard values) you can get a rough idea of where you are, close enough for the crystal harmonics to be heard. Some highe frequcny crystals such a42 or 4 or 8 MHz can provide good rough markers, too.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 27, 2019, 07:39:30 AM
I hadn't realized frequency counters had gotten cheap (must be microprocessor technology doing it).  Last time I looked at them (college days, 1980 give or take a couple years) they cost as much as a low end new car.

For $20 or so, I'll probably just get one and call it good for actual operation, though I'm still interested in the methods used back in the day.

FWIW, I'm in the USA.  AM BC here runs from 540-1610 kHz; FM BC goes from 88-108 MHz.  The second harmonic of 500 kHz is just about the middle of the AM band.

So a combination of a very "dirty" Crystal oscillator and a suitable filter will give a usable frequency reference, and in the bands of interest, 500 kHz spacing of harmonics should be enough for calibration -- 7.000 is far enough from 7.500 for our purposes.  Seems simple enough.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: N8AUC on January 27, 2019, 11:13:18 AM
So, presuming I've built a nice, stable oscillator with a 500 kHz crystal standard, how do I select for a particular harmonic?  There will be a peak every 500 KHz until they're too weak to detect (if I build for a square wave, that'll be odd multiples up to 7x or 9x at least, though they'll be pretty faint by then).  A bandpass filter?  Frequency doublers to get into the range I need (7+ MHz)?

They're available in kit form for a very reasonable price.
Check this out...
https://www.eham.net/reviews/detail/9480
This one actually provides switchable markers at either 1MHz or 100KHz intervals, which is kind of handy.

This one is also very reasonable, and it will give you marker signals every 50KHz, 25KHz, 10KHz or 5KHz if you want it.
https://qrpguys.com/k7qo-marker-generator
A kit for $15? Can't beat that.

Then there's the frequency counter that N4MQ mentioned, which is even more useful.

Lots of ways you can go here, and save some ca$h along the way.

And yeah, back in 1980 you couldn't touch a frequency counter like that for less than a few grand.
I remember those days. I was still an undergrad EE student back then. Things have gotten WAY better since then.

73 de N8AUC
Eric



Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 27, 2019, 11:42:21 AM
I like tubes -- but I like saving money too, and I'm capable of recognizing when something can't be done at reasonable cost (or with usable accuracy) with technology I understand.  I'm not above using some magic, if it does the job I need done...

I'm also capable of soldering through-hole components on a PCB (wouldn't want to try surface mount, though) -- I built a metal detector kit in high school (1973) and it worked (as well as a small/cheap metal detector is going to).  Looks like I'm going to have to order some kits to build some tools.  Marker generator, frequency counter (I actually found a link on another thread for a combination crystal tester and frequency counter in kit form for under $10 shipped from China), maybe a few other things.  For a hundred bucks and a few hours assembly time, I can put together a tool kit that would have cost $50k when I left college.

That'll make building 1920s-1950s radio gear a lot easier.   8)


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on January 28, 2019, 03:39:52 AM
I seem to recall that in the mid 1980s, Sabtronic offered a 1 GHz counter for around $200.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC5UP on January 28, 2019, 08:29:01 AM
Sure did, but 1978 is more accurate...  I had one when I was living in Dallas and it was a kit product sold through a local swapmeet and magazine advertising.  Reasonable quality for the price but I had to visit their shop as mine didn't work.  I'm experienced with kits but not so much that I'd trust my work over the vendor so I took it back, they had glued small pieces of styrofoam top & bottom over the 10 MC clock generator for temperature stability.  PC board didn't like the glue.  No clock, no count, no joy.  No problems after that.

The other hot item at the time was a DSI counter and matching DMM.  Larger boxes but similar otherwise, at the time they were a killer combo as I had yet to experience the joys of an auto-ranging meter....


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G8HQP on January 29, 2019, 02:08:39 PM
Quote
There won't even be a calibrated dial on the RX, though I ought to be able to make up a log <=> frequency table by tuning known stations and noting the vernier log position (there are still a few AM broadcasts in the SW bands, and SSB operators sometimes mention their exact frequency).
You will need some sort of dial.

Quote
Sounds like I may need to build a frequency reference alongside my transmitter project.
Yes. When I was starting out I built a 1MHz crystal oscillator, which then fed divide-by-10 TTL to get 100kHz and 10kHz. I could then calibrate any receiver I built.

Quote
So, presuming I've built a nice, stable oscillator with a 500 kHz crystal standard, how do I select for a particular harmonic?
That is why you need some sort of dial on your receiver. Then when you hear a crystal harmonic you know which harmonic it is.

You will probably also need an absorption wavemeter, which you will need to calibrate somehow. Otherwise you will never know where you are transmitting.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 29, 2019, 04:18:38 PM
Well, I ordered an $8 combination crystal tester and frequency counter kit.  Assuming I can get it together in working condition, that should solve most of the problems.  For that kind of money, it was a no-brainer.

I won't be sure until it arrives how the scale works on the 4" vernier I ordered off eBay (some rotate the entire scale, others have a way to attach a pointer), but it and the smaller verniers I already have do have a "dial" that reads 0-100 as you turn the knob from one end of travel to the other.  With some means to calibrate that against actual megahertz (worst case, put the set into regen oscillation and read the frequency with a wire loop near the tickler, connected to the counter's input), I can either print up a scale, or make a chart of what log reading corresponds to what frequency.

That instrument ought to also let me directly read the frequency of my transmitter when tuning on a dummy load.

I'd have just ordered one in the first place, if I'd known such a thing could be had for under $10.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4OM on January 29, 2019, 04:32:10 PM
Those combo boards are based on DL4YHF's freq counter design. I have built several 4 and 5 digit versions of the counters. Wolf's website (search on his call) has several examples built by others. These counters are are aimed at 1 kHz resolution for dial readouts for transmitters and receivers.

Some of the inexpensive 10 digit counters on eBay are 1 Hz resolution.

Ted, KX4OM


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 29, 2019, 05:00:59 PM
These counters are are aimed at 1 kHz resolution for dial readouts for transmitters and receivers.

That's pretty much what I'm after.  Not only is that all the accuracy I need for things like meeting a sked on the right frequency, but it's good building practice.  If/when I need a 1 Hz resolution, I'll shop around for that.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: VK6HP on January 29, 2019, 10:03:29 PM
Reading the thread and your interests, I'm sure you'll have a lot of fun but equally sure that you'll discover for yourself quite a few realities, both in terms of making a usable older-style station and in making operations feasible alongside more modern gear.  But there are plenty of us who enjoy taking time away from bleeding edge technology to enjoy classic and historical radio, so hopefully you'll have plenty of enjoyable contacts.

One suggestion I'd make might seem a bit strange at first in view of your aims but you could look around for a decent receiver, preferably using tubes of course.  You can pick up classic receivers for not too much money and, armed with a crystal calibrator, they offer good bandspread and dial accuracy.  You get a nice box for the shack and perhaps get a functional station ahead of the super-regen receiver but, more importantly, you can use the receiver in a multitude of bench tests, including calibration of your home-brew equipment, assessment of oscillator purity and stability (electrical and mechanical), indication of harmonic and spurious outputs, and a whole host of other things.  

Older receivers come with enough challenges to have their own charm.  But even with very good test equipment, I still find a bench receiver to be very useful

73, Peter.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on January 30, 2019, 02:44:12 AM
A still useful piece of equipment that can often be found for under $50 is the BC221 frequency meter from the SCR211. Not only can it be used for frequency measurement, it is also useful for generating a signal of known frequency, checking transmitter for chirp and key clicks and on telephony, checking for gross audio distortion. Has the advantage that it doesn't 'pull' so much as a sensitive receiver when checking transmitter. The Russian copy was supposedly still being made in the early 1970s.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 30, 2019, 04:37:43 PM
One suggestion I'd make might seem a bit strange at first in view of your aims but you could look around for a decent receiver, preferably using tubes of course.  You can pick up classic receivers for not too much money and, armed with a crystal calibrator, they offer good bandspread and dial accuracy.  You get a nice box for the shack and perhaps get a functional station ahead of the super-regen receiver but, more importantly, you can use the receiver in a multitude of bench tests, including calibration of your home-brew equipment, assessment of oscillator purity and stability (electrical and mechanical), indication of harmonic and spurious outputs, and a whole host of other things.

That's actually a good suggestion I hadn't thought of.  I was thinking existing tube equipment was going to be collector priced, but I just clicked over to eBay and found several multi-band and shortwave tube receivers under $100.  I put in a lowball bid on an old Hallicrafter, we'll see what happens, but there were BIN listings too -- just a little out of the comfort range two days before payday.  When I can spend a little money, I should be able to pick something up that way and, as you note, have a calibrated dial and known working circuit.  I've been watching videos on "restoring" radios like that, too -- which mostly seems to amount to replacing old capacitors that are of types prone to failure, and testing the others, plus cosmetics (which I'm likely to skip since I'm not shopping for the wood cabinets).

I'll still build my own -- but if I have a good receiver, I might build the TX first.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: WB6BYU on January 30, 2019, 07:23:17 PM
The receiver local oscillator makes a good signal generator, too.


As a Novice I had a receiver that covered 4 - 11 MHz on one band - the width of the dial pointer was about
equal to the whole 40m band.  (It also had a small tuning knob, which I replaced with a larger one to make
it a bit easier.)  So even with the scale, it wasn't easy to find a specific frequency.  So I had to get clever.

To operate 80m I would set the bandspread knob to zero, swith the Band 1 (AM BC), and tune in one of
our local radio stations at 1470.  Then when I switched to band 2 the radio would be tuned pretty close
to the Novice band, starting at 0 on the bandspread knob (which made a couple turns - it was missing
a scale pointer.)  Rotating the knob about 180 degrees put me close to my transmit frequency.

The transmitter was a single tube affair, so there was no way to turn down the power for a SPOT function.
I certainly could hear it on the dial, but the receiver tended to pull on such a strong signal so I could only
get an approximate position.

On 40m I probably set the bandspread at mid scale and tuned in my transmitter.  It put me somewhere in
the ball park.

It is often possible to find approximate band edges by where signals start (especially in a contest).  I had
to align a transceiver in a logging camp in Alaska this way:  all I had was a 100 kHz crystal calibrator, but
I could determine which marker was which by where the signals changed from CW to SSB.  Once I could
calibrate the dial scale at one point, it gave me a good enough approximation of frequency over the band.

A simple crystal oscillator helps a lot:  you can set the bandspread scale to an appropriate value, tune in
the oscillator with the main tuning knob, and then use the bandspread to tune over a small range.

We didn't bother knowing the exact frequency:  if someone said, "meet me on 3.965", then we'd tune
+/- 10 kHz or more around that, to account for both the difference in dial calibration, but also because
the other station would have to find a clear frequency between the other stations on the band.

Zero beating the other station?  Not with crystal control:  we'd call on our crystal frequency and listen
through the whole 50 kHz band for replies.  (It really caused problems when someone with a transceiver
would call CQ at the top of the band, tune through the band looking for replies, then respond on the
calling station's frequency", because that isn't where we were listening.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on January 31, 2019, 04:31:22 PM
Well, and so the journey truly begins.  I just won an auction for a Hallicrafters S-120, 1960s vintage 4-tube AM/SW (top of AM up to 30 MHz in three bands) receiver, seller claims it was receiving stations without an antenna at the time of listing (presumably actually with the internal loopstick for AM), which strongly suggests the caps and tubes are at least good enough to operate.  I fully expect to need to replace the main power supply filter, and probably some bumblebee capacitors (a few minutes into a video on restoring this exact model when I paused to check the auction).  Hopefully it'll be in my hands in time to take to the club meeting a week from Saturday, so I can get an Elmer to confirm which caps I need to replace and which are okay even after 55 years (ceramics, good, paper and "bumblebees", bad, but what about electrolytic cans?).  If I've overpaid by a big factor at $25 and about the same for shipping, please don't tell me -- but the four working tubes inside are probably worth at least that.

It's been almost fifty years since I've actually worked on a tube set of any kind (took all the tubes out of my family's B&W TV and tested them to find out why it wasn't working like new -- inconclusive, as I recall, but they bought a color set soon after despite it working as well as before when I was done), so this should be fun.  I've already downloaded the operating manual and schematic.

The dial won't be anything like accurate enough to tune a transmitter by (as described by WB6BYU, the needle will likely obscure most of the 40m CW band, even with the much wider window), but I should be able to follow harmonics from a crystal oscillator up the bands.  If nothing else, I can use it to listen to Radio Cuba, BBC, and Radio Moscow when I get a decent antenna up.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: VK6HP on January 31, 2019, 04:48:42 PM
Well, that was quick :)

One thing you absolutely have to be aware of is that the S-120 looks like it is a transformerless design, meaning that the operating voltages come from circuitry connected directly to the mains.  You have to be extremely careful and, for strong preference, run it via a mains isolation transformer.  I'm not an expert on North American "hot" chassis products but the starting point is to make sure that the "cold" side of the mains (not the active) is connected to the chassis.

Good luck, and be very careful.



Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 01, 2019, 02:22:41 AM
Well, that was quick :)

One thing you absolutely have to be aware of is that the S-120 looks like it is a transformerless design, meaning that the operating voltages come from circuitry connected directly to the mains.  You have to be extremely careful and, for strong preference, run it via a mains isolation transformer.  I'm not an expert on North American "hot" chassis products but the starting point is to make sure that the "cold" side of the mains (not the active) is connected to the chassis.

Good luck, and be very careful.



That's a very good point.  I've heard references to this, including "curtain burner" resistive cords to drop voltage before a simple rectifier/filter power supply.  I think curtain burners were gone by 1960, but I just looked at the schematic, and you're correct, there's no power supply transformer.  One wire of the power cord goes direct to the chassis "ground".  The simple fix for that is to install a new power cord with polarized plug (or put a polarized repair end on the existing cord, at least) to ensure the chassis connects only to the neutral leg (these plugs have a wider prong on one side, so they can be connected only one way).

Looks like the hot wire goes (via rectifier and filter) directly to the plates (110 V plate voltage) on three of the four tubes (the other one is marked for 68 V, not sure yet how they get to that figure), hence such ferocious hum if the filter cap is bad.

I fix power tools for a living, and (seeming alone among the techs in my shop) I'm well aware of the hazards of 60 Hz mains current.  Thirty milliamps is the figure -- the amount that will send your heart into fibrillation, and kill you if someone else doesn't get you restarted.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on February 01, 2019, 04:27:01 AM
Quote
The simple fix for that is to install a new power cord with polarized plug (or put a polarized repair end on the existing cord, at least) to ensure the chassis connects only to the neutral leg (these plugs have a wider prong on one side, so they can be connected only one way).

But check that the wall socket is correctly wired - some have found that wasn't the case!


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 01, 2019, 05:22:56 PM
Quote
The simple fix for that is to install a new power cord with polarized plug (or put a polarized repair end on the existing cord, at least) to ensure the chassis connects only to the neutral leg (these plugs have a wider prong on one side, so they can be connected only one way).

But check that the wall socket is correctly wired - some have found that wasn't the case!

Yep, I've seen them wired wrong myself.  Easy enough to check.  There's also an easy alteration to the radio (http://www.geojohn.org/Radios/MyRadios/S120/S120.html (http://www.geojohn.org/Radios/MyRadios/S120/S120.html)) to prevent the chassis from being hot even if the outlet is miswired; I'll be doing that.  I might also add the improved BFO from that page, though I've seen other references that suggest what's marked as a BFO is actually a regenerative selectivity enhancer (hence some folks thinking it's a bad BFO) -- that fits the manual references to that control, too; it operates like regen control in terms of tuning assistance, SSB and CW, as well as what sounds suspiciously like "exalted carrier".


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 03, 2019, 09:51:19 AM
 :o I'm amazed.  The S-120 arrived today, postal van pulled up and honked.  Yes, that's Sunday delivery, for an eBay item I paid on Friday!  The radio looks really clean, too -- if anything, the eBay photos barely did it justice.  I still need to check for chassis isolation (and at least mark the chassis connected prong, pending cord/plug replacement) and look under the chassis for replaced or original capacitors before I power it up (not so much concerned about letting smoke out, but sellers do exaggerate from time to time and don't always know what they're doing).

Then there's the issue of trying to get a signal inside a metal box (mobile home) or improvising an antenna -- but I'll leave that for after the smoke and hum checks.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: WB6BYU on February 03, 2019, 11:21:10 AM
Quote from: ZEISSIKON

...I might also add the improved BFO from that page, though I've seen other references that suggest what's marked as a BFO is actually a regenerative selectivity enhancer...


A set with the regeneration applied at IF rather than at RF was sometimes called a "super-gainer".

I had a set that worked that way:  it had a regenerative IF stage that was adjusted similar to a regenerative
receiver:  on AM it increased gain and selectivty, the same function as a "Q-multiplier" (which was just an
external circuit that added regeneration to an IF stage.  On CW the regeneration control was advanced to
where the stage oscillated to function as a BFO.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC2EU on February 03, 2019, 11:31:35 AM
I had ( and still have) a s-120 as a kid.
You will find that it doesn't have enough bandspread to dial in stations when the bands get  crowded.
Each bandselect on the s-120 covers a whole lot of MHZ!
Conversely , many of the old communications radios only have only 500Khz spread over the ENTIRE DIAL per amateur band.
Also, The s-120 has a diode detector and BFO rather than a product detector.

All in all SOME receiver is better than none. It's a good starting point to learn the "ins and outs" of radio.
Have fun and welcome to the hobby.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 03, 2019, 03:49:44 PM
Apparently (based on the reviews here on eHam) there's considerable difference of opinion on how good or bad the S-120 is -- I suspect that has a lot to do with condition.  I've had mine for a few hours now; verified with my multimeter that there is no connection from either cord conductor to the chassis (at least when powered down -- hard to test with power on), and based on condition took a chance and powered it up.

I haven't opened the case yet, but I'm going to bet someone has replaced the critical capacitors already; I've got a pretty dirty 60 Hz hum across the AMBC band but a strong station will cover it (it's completely inaudible when I tune WKTE 1090, which has its tower a few miles away on a mountain top); I suspect it's from aquarium pumps, wavemakers, and fluorescent lights in the next room from my designated shack.  With the internal loopstick I was able to pick up three local stations, even inside the Faraday cage I call home, and attaching the telescoping whip antenna (about 1 m long) found me pulling in a few stations in every SW band -- one that I believe was from Spain, CHU frequency/time broadcast from Ottawa, a number of other Spanish-language stations, and what I believe were pirate stations broadcasting music in (or just outside) the 15 m amateur band.

I was disappointed to be unable to hear WWV again before it goes off the air, but I'm fairly sure that's because it's in Colorado, more than twice as far as with a range of mountain between compared to Ottawa.  If I can get an outdoor antenna up, I'm confident I'll be able to hear it; CHU was clear enough to copy the time announcements easily with the limited antenna I have.

A short break after that first tune-through, and I went back and was able to tune a pair of overlapping or very closely spaced CW stations (both within the narrowest band I could tune) in the 40 m CW sub-band, an SSB conversation in 40 m, and another SSB ragchew in 80 m -- all with a 1 m vertical inside a metal-clad house.  All of this was before dark with everyone getting ready for the Big Game (can't call it by its name, lest the trademark owners appear with thunderbolts and lawyers).  SSB is hard to tune well enough to make sense of the words.  CW will likely be better after dark, and with more antenna.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: G3RZP on February 03, 2019, 04:07:50 PM
Sounds like you are getting ready to appreciate(?) the pleasures of the poor performance of receivers of yester year. Yet back in 1948, there was a guy in the UK - a coal miner by trade - who built himself a three valve TRF receiver and had over 50 countries confirmed as an SWL on 160m in 1948.....He could make that TRF sit up and beg! His name was Bob Iball and he passed away many years ago now. I suspect that there are now very few of us left who remember him and his skills as an SWL...


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: N3DT on February 04, 2019, 04:00:46 PM
My first RX was an S38E in the 50's. Now that thing was a bear to tune, but with the novice crystals I had and listening to the band I could figure out where I was. Seems to me the bandspread worked backwards so I figured how to dial in the main dial so I could tune up from 0 on the bandspread and the novice band maybe covered 1-10 out of 100. Anyhow I got it to work somehow and the DX40 I had with crystals was fixed. I used that for years without problems. Mostly 40M because I had a 40M dipole outside my dad's house. But it wasn't ideal. First good RX was a HQ145 and that worked great. Real calibrated bandspread. What a difference. It wasn't until the mid 70's I got my first SS transceiver, FT757GX. I'd been off the air for many years and then I got my Extra. That was a treat. Somehow I didn't forget the code.

If you can hear CHU at 7350 or whatever it is that's a good start to figure where 40M is.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 06, 2019, 04:12:08 PM
I'm not sure what I've been hearing would qualify as "poor performance".  Much/most of the 60 Hz hum I had vanished when I unplugged the 8 ohm headphones I was using to try to keep a high whistle (beyond my hearing range, which quits between 10,00 and 12,000 Hz) from driving my partner nuts two rooms away.  On speaker, the hum is barely noticeable.  Further, with just the whip antenna, I was picking up some stations I'm certain were at least a thousand miles away.  Overall, I don't think this S-120 is performing badly.  Get a good antenna up, and I might decide I don't need anything better before I have a transmitter or transceiver.  Listening is handicapped by living inside a metal box, and more so by being down in a valley.

Now, that said, I've never tried to listen with a modern SDR or IC radio.  The last time I had access to a shortwave receiver was around 1973, and that was a near-new (then) transistor set with a similar band setup and no bandspread control -- and it did little if any better on shortwave than this Hallicrafters.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC2EU on February 06, 2019, 06:04:37 PM
Now, that said, I've never tried to listen with a modern SDR or IC radio.  The last time I had access to a shortwave receiver was around 1973, and that was a near-new (then) transistor set with a similar band setup and no bandspread control -- and it did little if any better on shortwave than this Hallicrafters.

If you are comparing apples to apples, there is no difference.
If you were using a 1932 Atwater Kent , then moved to the S-120, you would be duly impressed by the difference. The same goes if you upgrade to a real communications receiver. Even an ancient R390 ,which is older, would blow your socks off. 

If it's working for you , then that is all that matters at the end of the day. I don't have the "ultimate" radio either, just  a lowly FT450d, but it works for me at the moment...yet it is still way beyond the Halli s-120.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 07, 2019, 02:32:21 PM
Okay, with no basis for comparison, I'll have to take your word for it.  Which brings the question to, how do I identify a "real communications receiver" when I'm shopping on eBay?  No, going to a local swapmeet won't work, there seems to be only one near here per year and it's in the fall.

I've seen listings for Hallicrafters S-119, which seems to have about six or seven additional controls compared to this S-120.  Those come in around $200 -- which is close to the limit of what I can spend right away.  If I need to spend more than that to get "way beyond the Halli s-120", it's even more important that I be able to tell the good from the merely complex before I tickle PayPal and send off a bunch of money.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: W9IQ on February 07, 2019, 02:45:25 PM
Hmmm... this somehow sounds familiar...

When looking at legacy receivers, a key differentiator is often general coverage (shortwave) vs amateur radio coverage. Most shortwave receivers lack the band spread, selectivity, filtering and demodulation features needed for practical use as a receiver for a QSO. Receivers targeted primarily at the ham radio community tend to have better overall features for ham use.

The next major differentiator is the superheterodyne architecture that represents the epitome of legacy receiver architectures.

Having selectable filters such as 3000 and 300 hertz can help to cut adjacent QRM.

A notch filter can help to cut an offending signal or noise.

If you have a computer (even a Raspberry Pi 3) and are willing to invest $200, you can get a state of the art software defined receiver. An example of such a receiver is the Airspy HF+. It is an amazing piece of hardware for the price and will give superior performance to many heterodyne receivers. It even allows you to operate it over the Internet.

For slightly more money, you can purchase an SDR transceiver such as the HackRF One. This will eliminate the need for frequency spotting and transmit/receive relays or PIN diode switching that you would need to accommodate with a separate transmitter.

If you are not familiar with SDR receivers, there is a  network of them on the Internet at websdr.org that are free to use.

- Glenn W9IQ


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 07, 2019, 03:12:36 PM
Thanks for the paste, Glenn.  Never mind that none of that stuff is visible in an eBay listing

What I already have is a superheterodyne, and people are telling me it isn't suitable as a station receiver.  It sounds like you're suggesting I really need "modern" equipment.  If I could spent $1000 on a whim, and wanted the latest and greatest equipment, the problem would be solved.  But look on eBay, and everything with one or more shortwave bands on the dial is a "communications receiver."  There are probably a hundred models, from the 1940s to 1960s, that will fill my bill, and likely five times as many that won't -- but I don't know how to reliably tell one like Bill Cosby had as a kid ("two hundred and forty seven knobs, of which only two worked: on-off volume, and tuning") from one that will separate two CW operators who are both using the same crystal, but one has a tuning circuit and moved off the crystal fundamental by a few kHz.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC2EU on February 07, 2019, 03:29:18 PM
Okay, with no basis for comparison, I'll have to take your word for it.  Which brings the question to, how do I identify a "real communications receiver" when I'm shopping on eBay?  No, going to a local swapmeet won't work, there seems to be only one near here per year and it's in the fall.

I've seen listings for Hallicrafters S-119, which seems to have about six or seven additional controls compared to this S-120.  Those come in around $200 -- which is close to the limit of what I can spend right away.  If I need to spend more than that to get "way beyond the Halli s-120", it's even more important that I be able to tell the good from the merely complex before I tickle PayPal and send off a bunch of money.

The blurbs on Ebay won't help to separate the good bad and ugly because there isn't enough detail.
If you see something interesting, do more research on it . Find the spec sheet and read reviews, etc.
A good one would have sensitivity around 0.25 microvolts or less the s-120 is probably 1 microvolt or more.
If you want something old, look at the collins 75A-4 , it even has a product detector! - but it will need more maintenance than the newer stuff.
A newer one might be something like Icom IC-R75. (DDS with no "bands")
As I mentioned before, the important difference in a communications receiver is bandspread. for instance , the entire dial start to end is only
550KHZ , just enough to cover the entire 80 meter band, instead of being a 1 inch section of a 12 inch slide rule dial.
the old ones would have more "bands" to cover HF because the bandwidth is greater.
On the newer ones it's in terms of 'resolution"; 10Hz is typical.  You want as much resolution as your wallet can afford.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: W9IQ on February 07, 2019, 03:50:42 PM
Thanks for the paste, Glenn.  Never mind that none of that stuff is visible in an eBay listing

What I already have is a superheterodyne, and people are telling me it isn't suitable as a station receiver.  It sounds like you're suggesting I really need "modern" equipment.  If I could spent $1000 on a whim, and wanted the latest and greatest equipment, the problem would be solved.  But look on eBay, and everything with one or more shortwave bands on the dial is a "communications receiver."  There are probably a hundred models, from the 1940s to 1960s, that will fill my bill, and likely five times as many that won't -- but I don't know how to reliably tell one like Bill Cosby had as a kid ("two hundred and forty seven knobs, of which only two worked: on-off volume, and tuning") from one that will separate two CW operators who are both using the same crystal, but one has a tuning circuit and moved off the crystal fundamental by a few kHz.

My modern recommendation was $200 - I don't know where your $1,000 comment comes from. The $200 version will beat out any legacy receiver for comparable dollars. Don't bother with eBay to buy the new technology - get brand new with a warranty from a reputable dealer for only $200.

- Glenn W9IQ



Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: VK6HP on February 07, 2019, 08:33:55 PM
I'm pleased that you took up my suggestion and got a receiver and, performance shortcomings not withstanding, you'll undoubtedly get a lot of fun out of it for not a big investment.  As the previous two posters have suggested, you can usefully spend a bit more time researching your next receiver.  With due respect, everyone starts from a "don't know what I don't know" situation and we all progress from there (well, most do).  One very valuable thing you could do is to link up with a local radio club, or some individual hams.  That way, you'd form some idea for yourself about the spectrum of performance of various radios, all of which may be labelled "communication receivers". Believe me, that label is downright imaginative in some cases!

To give you an example of the wide performance range you may encounter in tube receivers, I'm staring up at my restored Heathkit HR-10B, which I built as a teenager.  By most measures, it's a poor receiver.  But with ham band only coverage and OK sensitivity, I worked quite a bit of CW DX with it, using my one tube crystal controlled transmitter built from scrounged TV parts. The unstabilized B+ made me adept at copying code with all sidetone frequencies, especially as we lived at the end of a long SWER mains line in the bush. However, the HR-10B now gets many friendly glances from shack visitors, most of whom have no idea of how terrible it is.  (With the addition of some zener stabilization it's actually not quite as bad as it once was).

Looking a bit to the side, I see a Collins 75S-3 and 51S-1, both working as well as the day they left the factory (maybe better, in the case of the 51S-1).  These are serious receivers that lose little to modern HF radios, except for the lack of DSP noise reduction.  That may or may not be a factor, depending on your location.

I could go on, but in between the extremes, you could expect to pick up nice Drake R3 or similar for not a lot of money (almost certainly less than the Collins radios mentioned by me, and others).

Glenn and James have made some good comments, and you might get a bit more information from looking at our (and others') qrz.com pages.  But try and get yourself a bit of radio club activity and see what's out there in terms of equipment (homebrew and other) and performance.  Many hams are all too happy to help a newcomer and like nothing better than trying out various radios. 

73, Peter.



Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 08, 2019, 04:41:57 PM
Peter, I'm already having a lot of fun with the S-120 -- easily worth the $50 I've got into it.  "Bad" receiver or no, I put a better antenna on (the FM antenna that came with the Realistic stereo I bought in 1983, hung over an old dry aquarium on a shelf above my radio table), and about tripled the number of stations i could hear.  Last night, I was hearing overlapping CW stations, what sounded like FSK data, as well as AM and SSB.  I'm getting the hang of tuning the combination of main tuner and bandspread (which lowers the main tuning a bit as you reduce it, requiring two hands) and using the "BFO" (regen) to augment AM signals and make CW audible and SSB more or less intelligible.

The receiver came before the local club because the most local club meets on a weeknight, too late for me to attend and still drive an hour each way to work the next day.  The slightly less local club I chose instead (roughly an hour drive, instead of 30 minutes) meets the first Saturday of every month for breakfast (that's tomorrow), and I plan to be there, my S-120 in tow so I can both show what I have to work with so far, and learn more about how to get the most out of it (assuming there are still some Elmers there who remember vacuum tubes as something other than a cleaning accessory).

Glenn, you're missing the point I thought I'd made both here and on the Stack Exchange: if I can do the job with tubes, I'd prefer that over transistors, never mind surface mount ICs and SDR.  I don't need or want a waterfall display -- I'm not working sonar in a submarine.  My hearing isn't what it once was, but it's still good enough to pick a weak signal out of noise (and that's a learned skill, meaning I'll improve with time and practice).  The physics of propagation hasn't changed since the 1930s (though the current super-quiet sun doesn't help).  The superiority of Morse for getting a signal through with minimum radiated power hasn't changed (hence why I'm learning code, too).  And honestly, a part of the thrill for me is being able to build my own equipment, just as, for photography, half the fun is the smell of the chemicals and watching a print come up in the developer.

Once I have my license, I'm sure I'll build a small transceiver kit (the under $50 QRP type) to get on the air, but longer term, I want to work the world with a homebrew vacuum tube station, and I won't learn any more about that with a "magic" receiver or transceiver that has more computing power than a Space Shuttle.  This isn't a technology hobby for me -- I got tired of technology for its own sake when computers had megabytes, not gigabytes.  To me, this is a "building stuff and using it" hobby, similar to stick-and-tissue free flight model airplanes, rather than "install the radio and engine, then go fly" radio control.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: WB6BYU on February 08, 2019, 06:47:11 PM
Many of us have managed contacts with relatively "primitive" general coverage receivers.
They may not be ideal for that purpose, but can still be a lot of fun.

Some of the characteristics of a "good" receiver:

Sensitivity:  the ability to hear weak signals.  This typically is set by the noise figure of the
RF amplifier stage, or, in receivers lacking that, by the mixer stage.  A pentagrid mixer tends
to be noiser, for example, than a triode amplifier.  On HF, where received noise is often more
of a limiting factor than internal noise, this may not be as much of an issue.  A quick check is
to tune between stations and disconnect the antenna:  if the received noise level goes down,
then you are limited by received noise, and improving the receiver won't make much difference.
If the first stage is a pentagrid mixer, then it may help to add a low-noise RF preamp, but use
only as much gain as is needed:  too much makes the receiver more prone to overload.

Selectivity:  the ability to separate adjacent signals.  The regenerative IF stage will improve
selectivity with careful adjustment, and this may help with broadcast stations, but my
experience was that it didn't provide as much selectivity when it was oscillating to provide
a BFO for CW or SSB reception.  Typical bandwidth for SSB is 2 to 2.5 kHz, while for CW
a couple hundred Hz bandwidth will help pick individual signals out of what otherwise may
seem like a jumbled mess.  But to use such a sharp filter, the receiver frequency must be
stable.

Stablity:  the ability for a receiver frequency to remain constant over some period of time.
(There are other forms of stability, such as freedom from oscillations in the stages, but we'll
focus on frequency for this discussion.)  If the frequency shifts 500 Hz when your hand comes
close to the tuning knob, it probably will still work fine for AM signals, because they rely
on the transmitted carrier for demodulation.  But it will be difficult to listen to SSB or CW,
because they will shift to where the signal is unintelligible (for SSB), or even out of the
receiver passband (on CW).  The same is true for frequency drift, though a deft hand on
the tuning knob can sometimes counteract it.  The wider tuning range you are trying to
cover on each band, the smaller the capacitance across the tuned circuit at the high end
of the band, and therefore the more the frequency shift due to changes in capacitance as
devices heat up.

Tuning Rate:  how fast the frequency changes as you tune the tuning knob, often measured
in kHz / revolution.  Again, this isn't too much of a problem receiving AM stations, but for
SSB and CW you want a slow tuning rate, especially with narrow CW filters.  Even with a
large tuning knob, I find it uncomfortable to use a tuning rate of more than around 25 kHz
per revolution (for CW), and half that, or less, is better.


All of these can be improved by various sorts of modifications and/or additions to the radio,
though if the VFO itself isn't stable that may be more of a major upgrade.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: WB6BYU on February 09, 2019, 09:33:40 AM
One I forgot to add (and others are welcome to contribute as well):

Product detector:  a circuit designed for demodulation of SSB and CW signals
with minimum distortion.  You can introduce a BFO into just about any IF stage
(or even at the signal frequency) and get a beat note on CW, but a product detector
is a specific circuit designed for that purpose - basically a mixer that takes two IF
signals and produces the audio difference between them.  Many older receivers
didn't provide enough BFO injection to properly demodulates stronger signals.  That
usually meant that reception was best when the audio gain was turned up all the way
and the manual RF gain control was used to adjust the volume. The BFO would also
activate the AGC, so manual RF gain was really the only option.  With a product
detector you typically get more audio output for gage same RF input, and it handles
a wider range of signal strengths with minimal distortion.

If you add a product detector / BFO to your receiver then you can still use the IF
regeneration to control the selectivity when receiving CW, because it doesn't need
to oscillate tobprovide the BFO function.


Generally for Hallicrafters receivers, the S-xxx model numbers are for general coverage
and the SX-xxx models are ham band only.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 10, 2019, 02:40:15 PM
Thanks, BYU -- that was a much more useful explanation than I've had before.

However, someone pointed out something on Stack Exchange on Friday that I'd just realized the same day: I can get a transceiver for about the same money as a ham-oriented receiver, and then I don't have to worry about having a "matching" transmitter, setting up muting when I key down (to protect the receiver), having to manually switch the antenna from receiver to transmitter, etc.  I put in a bid today for a Heathkit HW-101 (80, 40, 20, 15, 10 bands, 100 W, dropping off to around 80 W on 15 and 10, SSB and CW), though I got outbid in minutes (and it didn't include a power supply anyway).  It looks like I can get a vacuum tube transceiver that will cover a range of bands for around $200 shipped, if I'm not in a hurry.  Any of the Heathkit SB-100 or HW-100 derivatives will do the job (100, 101, 102 -- but the 104 was when they transitioned to transistors, so less desirable for me).  Knowing what Drake, Knight, Collins, etc. models were similar would aid in searching eBay for used units.

Of course, those Heathkit transceivers tune only the amateur bands -- 500 KHz up from the bottom frequency.  That means they won't tune any of the frequency standard stations (WWV at 2.5, 10, 20, and 25 MHz, or CHU at 3.33 MHz), because all of those are outside the ham bands. Once I have a proper antenna up, my S-120 should be able to get WWV (as long as it transmits) and I can barely hear CHU in daytime, clearly at night, even with a crappy antenna -- but that's not much good for calibrating the transceiver's built-in frequency standard, especially with CHU not on a harmonic of 1 KHz.  Fortunately, I've got a frequency counter/crystal tester kit on the way, and I should be able to calibrate that against CHU and then use it to check the built-in frequency standard.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: WB6BYU on February 10, 2019, 09:33:46 PM
I've seen a number of functional HF SSB transceivers selling for under $200 at hamfests,
including Kenwood hybrids like the TS-520 (tubes in the driver and finals, otherwise solid
state) for $125 in working condition.  A Tempo-1 (also sold as the Yaesu FT-200/250) is
another option: reasonably common, mostly tubes, not as in demand by collectors.

And you can always build a converter to listen to other frequency ranges if desired.

The Drake rigs of that vintage were the the TR-4C transceiver (with variants), or the
R-4C receiver with the T-4X transmitter that could be interconnected to transceive.
That also permits the receiver to be used by itself, or tuned off frequency for "split"
operation (for example, where the DX is transmitting below the US phone segment
to reduce interference, but listening for replies higher in the band).

Collins rigs were KWM-2 transceiver, or the 32S-3B transmitter and 75S-3B receiver
(or something like that) though those demand higher prices from collectors.

National had the "NCX" line of transceivers, Galaxy had the GT-500 and GT-550, and
Swan had the 350 and 500 transceivers, plus the 250 on 6m (AKA the "Too-Drifty").
The Swan Cygnet 240 I think was later, and may have had some transistors.

Note:  All from memory:  I probably missed some (the Hallicrafters transceivers
tend to be more collectible) and I'll be happy to have corrections and additions
from others.  During that era I was using a Heathkit HW-12 monoband SSB tube
transceiver, so didn't pay that much attention to what else was available.

From Japan, Kenwood had some rigs prior to the hybrid TS-520/TS-820, and
Yaesu had several versions of the FT-101.

On some of these (including the KWM-2 and the Swans) CW was more of an
afterthought.

You do need to be careful with some of the rigs that used sweep tubes in the
final, as a new set may cost as much as the rig.  But if you get a really good
deal on one with bad finals, most can be converted to use 6146s.


Dial calibration isn't a problem:  I used a 100 kHz crystal calibrator that I could zero
against WWV on a general coverage receiver, then use to check every 100 kHz
kHz across the dial on the ham bands.  Those were standard in many rigs before
digital displays became common.



Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 11, 2019, 04:45:20 PM
Thanks!  So, other than Heathkit and Hallicrafters, Drake, Collins, National, Swan, Galaxy, and probably some others.

Honestly, if I can find one I can afford, I'd love to have a Heathkit SB-100 or HW-100 family unit.  CW or SSB on 80, 40, 20, 15, and 10, up to 100W out (dropping to around 80W on 15 and 10).  I may just hold off and save up until I can get one of those.  The 100, 101, and 102 are all tube, the 104 switched to solid state (possibly with 6146 finals).  Lots of them around (the HW-102 alone apparently sold around 40,000 units, according to one YouTube video), documentation of construction, testing, and modifications is easy to find, and they use parts that are generally still easy to find as well (common tubes).

Doesn't look like it would be impossible to build a replacement for the HP-23 power supply, either, if they turn out to be harder to get than the actual radio.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC2EU on February 11, 2019, 06:57:44 PM
Thanks!  So, other than Heathkit and Hallicrafters, Drake, Collins, National, Swan, Galaxy, and probably some others.

Honestly, if I can find one I can afford, I'd love to have a Heathkit SB-100 or HW-100 family unit.  CW or SSB on 80, 40, 20, 15, and 10, up to 100W out (dropping to around 80W on 15 and 10).  I may just hold off and save up until I can get one of those.  The 100, 101, and 102 are all tube, the 104 switched to solid state (possibly with 6146 finals).  Lots of them around (the HW-102 alone apparently sold around 40,000 units, according to one YouTube video), documentation of construction, testing, and modifications is easy to find, and they use parts that are generally still easy to find as well (common tubes).

Doesn't look like it would be impossible to build a replacement for the HP-23 power supply, either, if they turn out to be harder to get than the actual radio.

Going with Heathkit will definitely put you bidding against the collector crowd. Honestly, I don't see the attraction , other than nostalgia.
That's the beauty of this hobby, everybody 'has their thing".
I restore and operate WW2 radios for the heck of it. Not for performance, but for the 'experience" of doing the best QSOs possible with the crudest equipment. The ww2 stuff is a lot more rugged than Heathkit, too.



Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 12, 2019, 02:28:21 PM
The ww2 stuff is a lot more rugged than Heathkit, too.

No doubt -- but then, Heathkit stuff wasn't designed to mil-spec and intended to survive being torpedoed or shot down.

Yeah, I know, I'm wanting a collector radio.  I'll research the other brands and models mentioned above and see if I see anything that will do what an SB-100 will do (the HW family was essentially an SB of the same number with some bells and whistles deleted).

What I know I want: multi-band capability (at least 80, 40, 20, and 15; 10 is nice, but lacking a dedicated CW sub-band, less attractive for a base unit), a dedicated CW mode (RIT I don't care much about -- I can adapt to whatever CW tone is designed in, and most are close to 600 Hz anyway), VFO rather than rockbound, and good specs.  SSB is nice to have, of course; if something needs to be said quickly (i.e. emergency situation), I can talk a lot faster than I can send (even if/when I become a Morse maniac), and be more confident whoever hears can understand (and to that end, an AM mode would be welcome).  Ability to run on batteries is a plus (800 V for 6146 finals would traditionally require a dynamotor supply, but I'm not too proud to build a solid state upconverter for what's essentially an emergency/portable option on a base radio).  I don't need a huge amount of power; the 100W of the Heathkits I was talking about is about the upper limit I want to deal with, and I'd be fine with half that or less (plus the finals would be cheaper and/or run cooler) -- when I build my own TX it'll probably be QRP.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: AC2EU on February 12, 2019, 04:48:46 PM
If you were a solid state guy, you would probably like the rockmite QRP kit.

As a tube guy, it sounds like you would enjoy doing the ancient tube breadboard concept.
It's all very open (with the tubes plain to see glowing in the dark)and can be done in a modular fashion.

This is the ancient way: http://makearadio.com/tube/30bb.php (http://makearadio.com/tube/30bb.php)

this is a more modern way: https://hackaday.com/2009/11/20/tube-prototyping-station/ (https://hackaday.com/2009/11/20/tube-prototyping-station/)

And module concept that can be put on a larger board with other modules: https://www.instructables.com/id/How-to-make-vacuum-tube-breadboarding-sockets/ (https://www.instructables.com/id/How-to-make-vacuum-tube-breadboarding-sockets/)


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: WB6BYU on February 12, 2019, 06:34:44 PM
Most of the common SSB transceivers of the period will meet your needs, though there are a few exceptions.
Note the major shift:  AM rigs generally used separate transmitters and receivers, because the circuitry was
totally different.  But with SSB you had a lot of common circuitry (and you needed to be tuned much closer
to the other station), so transceivers became standard.

Most such rigs typically ran around 100 watts output from a pair of tubes (though power was still measured
as DC input to the final during the early years of transceivers).  The SWAN 500 and 700 ran more,
which could be hard on the tubes if you didn't learn to tune up very quickly.  And the Hallicrafters
Hurricane ran a full kW, which is about 600W PEP output by today's measurements.  (The SR-400 "Cyclone"
was the lower power version.) 

At some point SWAN had a 20/40/80m transceiver, and I think World Radio Labs (WRL) did also.  Sideband
Engineers had the SBE-33, 34, and 36, though at the last two had solid state receivers, and probably were
hybrids like the Kenwood TS-520/820/530/830 series.  (The TS-520 was one of the most popular ham rigs
of all time.  The SBE-34 (and, I think others in that series) didn't have a built-in CW option, but they sold
an accessory that fed a tone into the mic jack to generate CW (the Collins KWM-2 used the same approach,
but had the circuit built-in).  One disadvantage of this approach is the need for a high tone pitch (often
1000 Hz or more) to improve opposite sideband suppression.)


Most power supplies are relatively interchangeable:  they all used 600 - 800V on the final plates, 250 - 350V for
the other tubes, and a negative bias voltage, plus filament voltage (most rigs designed for mobile use could
power the filaments off the battery).   You may have to adapt connectors if you get a different power supply,
but they aren't difficult to build, either, especially if you can find a power transformer from an old tube-type
color TV.  (I do recommend using silicon rectifiers rather than mercury vapor tubes.)


And you're much more likely to find a good price at a local hamfest rather than on-line, not to mention the
shipping cost.  The Salem Hamfest is coming up this weekend if you are around NW Oregon...


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: VK6HP on February 12, 2019, 10:46:10 PM
It might also be worth mentioning that many of those old rigs with sweep tube finals and inflated input/output powers possessed no magic: if you want to run them respectably clean to something like modern expectations on SSB, they're 100-150W output radios.  A case in point is my FTDX560 restoration (all tube except the VFO) which does manage 300W CW output on the low bands.  I can of course also drive it to 300W PEP, but you wouldn't want to be a ham neighbour at the associated IMD levels.

But old does not equal dirty by any means: my 50 year old Collins 32S-3 transmitter is still just about the cleanest exciter around.

With the Heathkits, you can usefully consider what you really need in the radio because there are some subtle considerations that have arisen with the passage of time.  One thing to watch out for is SB-series LMO (VFO) fast instability, or warble, due to mechanical deterioration in the grounding scheme for the oscillator variable capacitor. While on the surface the HW series had the poorer (homebuilt) VFO, and coarser readout, it may in fact be more easily maintainable.  And, if you do get an SB series transceiver (having pre-built LMOs), the all-tube 100 and 101 oscillator is a bit easier to overhaul using widely available instructions.  I did manage to fix my SB-102 but working on the solid state TRW oscillator module was not easy.  Still, it was fun to get the radio going so well and, on a good day, I can tell myself that the SB-102 is a poor man's Collins.  (That belief holds until I go back to the Collins!).

The message is to compare the original specifications of any radios you may be considering, but also take the time to look at how time has affected the performance and serviceability of the units. 

73, Peter.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 13, 2019, 02:09:56 AM
Occurs to me that, in the end, unless I stumble into a trove of fifty different radios all priced at $100, what I wind up with will have a lot more to do with what I can find that I can afford, than what I'd really like to have.  I might even settle for building a Pixie, Mighty Mite, or similar transistor, crystal-controlled CW/QRP transceiver from a kit, just to get on the air while I look and save for the "dream rig."

For $20-$30 or so including a housing and a bag of crystals (key not included, in most cases), there's a lot of ability to wait for the right rig tied up in being able to make QSOs on 40m.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: HAMHOCK75 on February 13, 2019, 07:46:53 AM
Hamfest season if just around the corner. The first and last typically have some fine deals. I picked up nice Heath kit DX-35 once for $20 which covers 10-80M, 6146 final, AM/CW.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: KX4QP on February 13, 2019, 03:44:28 PM
Hamfest season if just around the corner. The first and last typically have some fine deals. I picked up nice Heath kit DX-35 once for $20 which covers 10-80M, 6146 final, AM/CW.

That'd work.  Especially since I'll likely be getting General instead of Technician (studying daily on hamtestonline).  CW capability is easy to cobble in, I'd think (HV relay to switch the B+?, keep that 800V off the key), but there probably aren't many ham transceivers that don't offer CW, especially from the era when that was all a Novice was allowed to use.


Title: RE: How to tune a particular frequency with homebrew, non-calibrated tuners?
Post by: K4CCW on February 14, 2019, 08:28:17 AM
I’ve just read this entire thread and would like to thank all contributors for a very interesting and informative thread.

And that’s from someone who's been in electronics for 60+ years and licensed almost that long.

These days I just enjoying restoring the boatanchors I used to lust after back when I first got into the hobby in the late 50s, but couldn’t afford.