LOL!

Great stuff .. I hear you brother :-)

73

--KC9KEP

Hello all,

I felt compelled to editorialize for a moment about home brewing (at about least vacuum tube equipment.)

Some of the most important aspects of fabricating homebrew equipment seem to be glossed over in the vintage ARRL articles.  Although the ARRL handbooks make what I consider to be casual references such as: Shield power supply leads, route control cables along chassis edges, keep input & output leads away from each other, these concepts seem to be critically imperative and should really be emphasized.

Although it’s water over the dam now (and probably trivial to those who have spent time in the trenches) for neophytes such as myself, these “gotcha’s” get me .. time and time again!

Of course, those with experience will recognize that the schematic diagrams are laid out to facilitate functional understanding of the circuitry.

I recall building the ARRL’s 1944 receivers and wondering why two capacitors would appear connected to a single wire lead in two different places.  “Why not use one capacitor of twice the value?”  Of course, they were trying to emphasize separate bypass capacitors for two places in the same circuit.

As W8JI said somewhere, “we must stop treating [RF] systems like they were DC systems”.

This morning, I stumbled upon the following article;  ARRL’s “Single Sideband” circa 1965 “Some Notes on the ‘Single Sideband Package’”

The article is similar to a recall of the preceding feature article.  It points out several pitfalls in the initial publication.  They’ve added steps such as:  mounting a metal plate across the [driver] socket between grid and plate prongs and grounding it, this stage was made stable”.

And in Ted Crosby’s HBR-11(which I had built), a construction techniques post-feature-article of tips on connecting components to the miniature tube socket were published.  The technique is to solder a 1” length of 14 gage wire vertically to the socket’s center ground provision and mounting components vertically to this grounded center lead.  Additional tips are shown for keeping front-end RF leads short, direct and made of 14 gage wire and so on.

So, I appears that others have been “bit” by these pitfalls as well.

At any rate, I just felt compelled to vent a bit.  I think I have spent more time chasing some of these instability issues than I did building the entire projects.  And I think the handbooks could have pointed these pitfalls in terms such as:  “The following layout is critical.  This circuit will not operate correctly unless you do the following ..” type of stuff.

But thanks to all who have been Elmering me along.   I will not be making some of these mistakes again!

73

--KC9KEP

OK Peter .. Good ideas for me to try.  Thanks!

Yes, the 6CL6 is running "straight" .. same freq in and out.

As a matter of fact, it was one ill that I thought I had cured.  At first,
I could get the squegging with the 6DQ5 out of its socket.
The 6CL6 would break into oscillations by itself.

Shielding the 6CL6 wire leads seemed to help, but it could still be a trouble spot.

I know what you mean about a coil next to L4 & L5 .. sort of a
cancellation effect.

73

--KC9KEP

Thanks guys :-)

GW3OQK suggested that I increase the value of the "300 pf at the bottom of the grid coil .. should be more like 1000 to 1500 pf."  Adding 680 pF to the 300 pF seemed to work well.

With the 6DQ5 plate voltage and cathode resistors disconnected, the neutralization capacitor seemed to work well.

I was looking at the 3 MHz signal at the transmitter output using a scope and adjusting the neutralizing capacitor for a null, which happens when the neutralizing capacitor is at about 75% meshed. 
After the 3 MHz signal was nulled, I swept the plate tank capacitor and there were no sudden peaks or jumps. 

There was another peak that appeared at the end of the plate capacitor's travel at 5 MHz, but this is the FT-243 crystal frequency (that gets hetrodyned with the 9 MHz "suppressed" carrier frequency). 
Since I wouldn't tune the plate tank to peak that frequency, I wouldn't see this as a stability issue.

But .. When I reconnect the 6DQ5 plate voltage and resistors, my problem comes back .. i.e., when peaking
both grid and plate tanks, the output pops up and oscillates.  The cathode current goes way up.  Numerous
harmonic lobes pop-up around the 3 MHz fundamental output frequency.

My spectrum analyzer shows these oscillations right on top of the main 3 MHz lobe vicinity.  There are
no oscillations higher up .. for example, nothing at 100 MHz on up.  I can audibly hear the amp "sizzle"
when this happens.

I did remove the audio pre-amp tube .. no difference.  This morning, I could agitate the oscillations by touching the frame of the FT-243 crystal.  Maybe RF is getting into the VXO chain?

Do you suppose the output section still needs some sort of neutralization?  It looked really good when
adjusting the neutralization capacitor with the 6DQ5 power disconnected.  Or am I barking up the wrong tree?

One other thing that I don't like.  The plate voltage is very high on the 6CL6 amplifier/driver.  The spec is
300VDC max but it measures at 355VDC.  (My first 6CL6 became intermittent last night and had to be replaced.  I
wonder if I should add some plate resistance.)

So, copious thanks again everyone.  (I'd hate to give up after all this effort!)

73

--KC9KEP

Hello,

Thank you all for your help with my circa 1965 SSB transmitter problems (posted earlier)! 
I believe I’m much closer to correct operation.

In my last messages, I did a lot of work by-passing DC points, adding shielding, re-dressing leads, etc.

I also peaked the resonance of L3/L4 and L5 tank/driver circuits by using my spectrum analyzer and located aluminum shielding cans to replace the previous steel cans.  I checked through the audio pre-amps and they look good (on a scope) to me as well.  The neutralizing capacitor does null the output with plate voltage removed from the 6DQ5.

The transmitter will operate until I peak both the Plate/Output tank capacitor and the Grid Tank capacitors at which point, it breaks into parasitic oscillations.  De-tuning either tank will reduce output level and cause the transmitter to stabilize.

I do believe that I’m seeing squegging; perhaps oscillations at multiple frequencies.  It is very visible on the scope and spectrum analyzer.

I can further adjust the neutralizing capacitor to stop these oscillaions, only to end up “chasing” the squegging.  If I eliminate it for one setting of the plate capacitor, it will re-appear at another setting of the plate capacitor.

As N3QE describes it, ‘[I can] see the choppy audio-frequency relaxation cycle quite clearly’ when at the threshold of squegging.  Peaking the tanks further causes oscillations across the spectrum and draws higher current in the 6DQ5. 

So, it appears to be the output section?  Time to re-dress more leads?

Thank you for any additional suggestions!

One comment; when these projects don’t work, one really starts learning ..

73

--KC9KEP

Hello

I've collected dozens of what I'd consider to be non-standard frequency FT-243 crystals.

I'm familiar with the idea of using the fundamental frequency and doubling/tripling so
that a specific crystal can be used for higher frequencies.

But I seem to have numerous crystals in the 8 MHz range.  Is there any way to make these
useful for the Ham Bands?  I understand that one can etch crystals to raise them in frequency
but I also understand that there is a limit to how far the frequency can be moved.

What were these frequencies originally intended for?  Military frequencies?

Thanks & 73

--KC9KEP

Thank you everyone for the help!

Last night, I discovered that removing the canisters that house the tank coils, greatly change the tuning.
This is no surprise, since these canisters are NOT aluminum.

(I knew this when I created the canisters but I had used what I could find.)  So, I'm running with
the canisters removed for the moment.

I also replaced three RF chokes.  Two of them appeared to be sintered cores.  I also replaced the
plate-choke with a NOS National 2.5 mH choke.

When disconnecting the plate voltage and two cathode resistors from the 6DQ5 output tube, I am
now able to easily adjust and null the output with the neutralization capacitor.  So, the is one BIG win for me.

At this point, the handbook says that I should check the low-level output with a receiver.

My FT-243 crystal is 5.240 MHz.  My SSB crystal is 9.0015 MHz.  (I read that when you subtract the
two frequencies, you get "sideband inversion" hence the 9.0015 MHz xtal for 80 meter operation.)

My target frequency is 3.7615 MHz.  My ICOM IC-730 is tuned to 3.7620 MHz.  (The IC-730
is not necessarily calibrate either.)

Here is a recoding of what is sounds like.  Can someone tell me is this is correct?
(This is what I mean about not knowing what I don't know :-)

http://www.bignick.net/ssb/KC9KEP_test.mp3

Thanks again!

73

--KC9KEP

Thank you everyone for your help on this project.  I’m starting to feel very dumb about now .. I didn’t think that I’d put so much time into this project and not get satisfactory results by now :-(

So, here’s what I’ve done to date:

-   Added six (6) 0.005uFD caps .. one to each filament connection.
-   Added 0.004 to the feed end of the plate choke to keep RF above deck.
-   Removed plates from the neutralizing capacitor.  (I did this before reading N2EY’s message .. )

Here are some photo's .. (Please let me know if I'm doing this correctly ..)

Here’s the choke bypass .. Hope I did this right.  I only had 0.002’s so I paralleled them.
http://www.bignick.net/ssb/choke_bypass.jpg

I don’t know if this was in my last photo’s, but I used braided leads to the Neutralization cap.
http://www.bignick.net/ssb/braid_to_neut.jpg

Here’s the 6DQ5 w/added filament cap.  There already are bypass caps on pins 3 and 6 as indicated in the schematic.  Are these leads too long?
Voltages as follows:
Pin-1 Grid (-107VDC) key up, (-81VDC) Key down.
Pin-8 Screen 148VDC
Pin-3 Cathode 0.0VDC Key up; 0.288 VDC, key down; (across a 27 Ohm Cathode resistor = ~11 mA)
Here's something that I didn't know - Plate Voltage - Key up 1,066VDC, Key down; 966VDC.
Could that be causing too much gain?  I'm using a Hammond 278X transformer; 800V CT 200MADC.
http://www.bignick.net/ssb/6DQ5.jpg

Here’s the 6CL6 w/added filament cap.  The plate voltage is ~355VDC which seems high.  Cathode is about 5.56VDC.  Grid to ground is 0.012VDC so I suppose the grid is negative relative to the cathode?  I didn’t see any parasitics.  The tube manual says that pin-7 goes to cathode but ARRL has it indicated as connected to ground?  It already has a 0.01uFD bypassing its screen.
Pin-8 (screen) is 245VDC.
http://www.bignick.net/ssb/6CL6.jpg

Here’s the 6BA7 w/filament cap.  It already has a 0.001uFD cap bypassing its screen.
http://www.bignick.net/ssb/6BA7.jpg

Here’s the 6AU6 w/filament cap.  0.001uFD bypasses pin-6.
http://www.bignick.net/ssb/6AU6.jpg

Here’s the 6CG7 w/filament  bypass cap.  Not much to bypass ‘cause it’s a triode.
http://www.bignick.net/ssb/6CG7.jpg

Here’s the driver cap between 6CL6 and 6DQ5.  It’s rated at 630VDC.  I’ll need to find a larger voltage replacement.
http://www.bignick.net/ssb/driver_cap.jpg

Here’s an under the chaassis view.
http://www.bignick.net/ssb/under.jpg

Filament voltage measures 6.7 VAC with 110VAC line voltage.  Is that too high?  If so, how could I correct it?

Do you suppose that I should re-dress those fat RF leads?
The driver tube runs very hot, but the plate is not red.
Some of the tubes have redundant pins.  Should these be connected?

Note:  Instability happens with the 80 meter coils but not the 20 meter coils.  I’m not sure if this is a clue.  Also, last night I had connected my Rigol DSA815-TG to the output section with the transmitter powered down.  I injected the tracking generator at pin-6 of the 6CL6 and the input to the analyzer to the coax output.

I could easily see that I could peak and move the peak resonance for 80m.  But, there is a second strong peak at 1.5MHz as well as the desired 3.5MHz peak.
I don’t know what is causing the 1.5MHz peak or if it’s an issue or not.

Bottom line – unfortunately, no discernible change.  Looking at the output with the +700VDC, 27 Ohm and 5.1K resistors disconnected, the output is minimum when the Neutralization capacitor plates are full open.  I have yet to try and additional 10 p in series.   I’m not certain that I could get the neutralization leads any shorter or more direct that they are.  I’ve replace the old “White-Wire” with a heavy gage single conductor.

I’m out of time for now but will pick up on this again soon.

Thanks again!  I’m stuck!

73

--KC9KEP

Hello all,

I really appreciate everyone’s help on these projects!  Part of the issue for me is “I don’t know what I don’t know”.   Sometimes it’s a real challenge to even determine what part of the circuit has an issue ..

This project is the 1965 ARRL filter sideband transmitter.  It features a McCoy type filter and sideband crystals.

http://www.bignick.net/ssb/281_.pdf
http://www.bignick.net/ssb/282_.pdf
http://www.bignick.net/ssb/283_.pdf
http://www.bignick.net/ssb/284_.pdf
http://www.bignick.net/ssb/285_.pdf

Pictures of my project:

http://www.bignick.net/ssb/top_front.jpg
http://www.bignick.net/ssb/top_rear.jpg

I had much trouble just getting as far as I have.

First, I couldn’t get *any* drive to the output.  After days of researching the circuits and tracing wires, I discovered that I had installed a 47K Ohm resistor rather than the required 47 Ohm!  DOH!

Then, I had major instability in the output section.  Part of the problem was solved by shielding various power leads.  Shielding the 6DQ5 didn’t seem to help much.  (Note, white-wire is the neutralization lead.)

http://www.bignick.net/ssb/shield.pg.jpg

Then, I read that VHF oscillations (I was getting about 145 MHz) can be caused by poor wiring of the output tank.  Fat, direct wires fixed that.

http://www.bignick.net/ssb/fat_wires.jpg
http://www.bignick.net/ssb/fat-wire.jpg

Then, I could see that the 8.9985 Hz was getting into the audio pre-amp, so I moved the crystals to a more remote location.

http://www.bignick.net/ssb/crystals_moved.jpg

One problem I have not fixed is the neutralization.  When I remove the 700VDC, 27 Ohm and 5.1K Ohm cathode resistors from the 6DQ5 and adjust the neutralization capacitor for minimum output, the null occurs when the capacitor is full open.  I think the output is more stable with the neutralization capacitor disconnected.

http://www.bignick.net/ssb/neut_cap.jpg

And .. I am able to transmit to my ICOM IC-730 while connected to a dummy load.  But, the audio sounds as if one were talking into a ventilating fan .. Any ideas what this symptom is telling me?

And, probably most troubling is that the transmitter is generating very little power output.  It’s barely moving the needle on my cross needle meter.

I went back to peak the L1 and L2 coils in front and after the SSB filter.  When they are peaked, I get more carrier output (maybe 20 watts), but I should not be seeing any carrier in the output for SSB.  The ARRL book says nothing about adjusting these coils.

And .. the 6CL6 amp runs VERY hot.  I can see the tube shield blistering.  Is this normal?  The voltages look good to me?

http://www.bignick.net/ssb/hot_6CG7.jpg

Incidentally, my test set up is:

Power to transmitter via isolation transformer and Variac. 
Transmitter output to current tap, power output continues to Cantenna load.  Current tap goes to 50 Ohm load, 10 dB attenuator to scope and 10 dB attenuator to Rigol; DSA 815-TG.

http://www.bignick.net/ssb/curremt_tap.jpg
http://www.bignick.net/ssb/rigol.jpg

I know this is a lot of info but any help is appreciated as I correct one issue at a time.

73

--KC9KEP

I built the NorCal FCC-1 frequency counter and Signal Generator combo a while back.

Hot air gun, tweezers, magnifying glasses and a little patience, but no problem-o at all :-)

--KC9KEP

Jim,

This is all great information .. thank you for taking the time to put this together!

I'll to get back to the project later this week.  I had neglected to mention what
voltages that I had initially measured (with the initial -22.5VDC bias), but here they are:

B+ Supply (Modulator off) = 810VDC
B+ Supply (Modulator on) = 732VDC

Low V Supply (Modulator off) = 316VDC
Low V Supply (Modulator on) = 285VDC

(The original schematic says B+ should be 600VDC and L.V supply 230VDC.)

Voltage across 50 Ohm Cathode resistor (Modulator on): 6VDC
Cathode Current (Modulator on) = 6VDC/50 Ohms = 120mA

Of course, the cathode current had dropped to 50 mA when I increased the bias
to -36VDC.

But, thanks again, I will return to this project soon.  (Maybe it would be easier
to replace the existing power transformer with one that has lower B+ output?)

73

KC9KEP

Could someone please help to understand more about this topic or kindly direct me to an appropriate resource?  (The ARRL handbooks don’t go into much detail about this.)

I’ve recently constructed an AM modulator using 807 tubes.  The original design calls for a -22.5V “hearing aid battery” to be used to bias the tubes.  I had used (2) 9VDC and (3) 1.5VDC batteries in series to generate a bias of about -22.5 VDC.

However, my power transformer provides a higher plate and screen voltage than what the original design had called for.  Also the original design suggests that the bias be set so that the cathodes indicate about 50 mA of current draw at idle (The cathode current is monitored by measuring across a 50 Ohm cathode resistor.)

Although my output waveform looks very nice on the scope, the 807’s are running hot and I was seeing some plate redness.  And, measuring the voltage across the cathode resistor, I had calculated about 125 mA of current draw.
So I reasoned that if the plate and screen voltages are higher than specified in the article, the bias should probably be more negative as well.

So, I tried (4) 9VDC batteries to yield a bias voltage closer to -36VDC in an attempt to bring the cathode current down to the specified 50 mA.

At -36VDC bias, the cathode dropped perfectly to 50 mA and I thought all was good.  But .. looking at the modulated wave on the scope, the wave shape doesn’t look as sinusoidal as it did with the -22VDC bias .. the rise and fall of the waveform looks more “straight” than curved.

So, then I reasoned that although I’ve “corrected” the cathode current to 50 mA, this may not be the appropriate bias for my higher-than-called-for plate and screen voltages.

Now, I am wondering how this balancing act should be correctly performed.

Should I simply add an adjustable bias supply that allows me to adjust the bias somewhere between “too hot” and “poor linearity” while monitoring output on the scope?  (Maybe trapezoid test?)   Or is there a specific method or tables indicating how to setup the operating bias for a push pull class AB1 amplifier?  Maybe the idle current needs to be higher than 50 mA when running the modulator at higher than specified plate/screen voltages?

(Note, to check the performance of my modulator, I have been connecting it to my 6146B transmitter; modulator transformer in series with the 6146B plate supply, and to 6146B screen via dropping resistor as indicated in the construction article.  I have been using 1 KHz audio test signal.  I monitor transmitter output into a 50 Ohm “Cantenna” load via a current monitor, a small torroidal transformer.)

Thanks all!
--KC9KEP

Thanks for the kind words, guys..

GW3OQK - Most round holes were cut with Greenlee punches.  The large circular hole for the modulation
transformer was cut with an adjustable circle hole cutter. 
(It has an arbor and adjustable "arm" and cutting bit.)

The rectangular hole was cut with a sabre saw with a metal blade, then filed to finish it nicely.

I cover the entire chassis with masking tape before marking and cutting.  After all the holes
are cut, I remove the protective masking tape.

Hope that helps :-)

73

-- KC9KEP

Hello,

I am building a circa 1953 AM Modulator to go along with my 6146B that I had posted
questions about earlier.

I think that it's working fairly well, judging by my power meter and scope trace display.  I have
yet to make a QSO or to get on the air yet (I've just got it operating today).  I have the modulator
connected to my 6146B transmitter and am measuring about 60 Watts output. 
(The modulator is connected to both the Plate Supply to the 6146B and Screen of the 6146B
via a "dropping" resistor.)

One concern that I have; The B+ in the construction article is stated to be around 600VDC,
but my power supply is about 80VDC higher.  I was thinking that perhaps I should have increased
the battery bias supply, but it seems to be working well as it is.
There is a 50 Ohm cathode resistor included in the design that allows the operator to monitor
the cathode current (but I have yet to do so).

Anyway, here are some images.  I am curious to see what others think of this design :-)

http://www.bignick.net/Mod/before.jpg
http://www.bignick.net/Mod/rear_1.jpg
http://www.bignick.net/Mod/under.jpg
http://www.bignick.net/Mod/Temp_Front.jpg
http://www.bignick.net/Mod/front_cab.jpg
http://www.bignick.net/Mod/rear_cab.jpg
http://www.bignick.net/Mod/top_cab.jpg

Scope Trace:

http://www.bignick.net/Mod/scope.jpg

Schematic wiring diagram:

http://www.bignick.net/Mod/Mod_2.jpg

73!

--KC9KEP

GW3OQK,

Yes, I've noticed that the parasitic suppressor has been moved in the schematic diagrams for
all the newer versions of this transmitter in the ARRL handbooks.

Another nit that I've noticed is that several extra "fly-specks" are present in the 1965 schematic
that usually indicate multiple connections at a given wiring junction.  These extra fly-specks go
nowhere .. i.e., they are situated where a wire takes a 90 degree turn.  It's as if someone was
editing the schematic and didn't finish the job ..

(I think they're called "fly-specks" .. the little "dot" that indicates that two wires connect where
they cross each other)

73

--KC9KEP