The AM Forum

My beautiful Valiant no longer has audio or that satisfying 'thunk or kerchunk' when squeezing the PTT. I'm sick because I did it myself.

The lineup has been from a Kenwood MC60 mic, through a W2IHY equalizer, to the audio in on the rear of the Valiant. The idea of using a Kenwood mic on the Valiant just seemed, well, wrong. I had a couple of old non-amplified D-104s around and just picked up what looks to be an almost new 10-DA microphone. I was trying different combinations of cables, mic heads and settings when suddenly - poof. No smoke, but no audio either, even going back to the Kenwood mic that always worked. Obviously I screwed something up by crossing a wire or something. I don't know.

I have to walk away from it now because I'm so mad I cold spit nails over my stupidity.

Why are you so sure that you broke it? Valiants are quite capable of breaking themselves. The two I owned in the past were quite talented like that.

Every time I turn my Valiant off after a QSO I appreciate that nothing failed. Another owner sold his because it "spent more time on the workbench than in operation". Still, I really like my Valiant and wouldn't think of parting with it.

With all that plugging in and unplugging, it sounds like it could be something simple like a connection failure. Does the rig transmit a carrier? Is your observation based on no kick of modulator current or not hearing yourself on a receiver?  Does your Valiant still have the original mic connector or something else?

Unless the PTT circuit was modified, the mic connector has over -150 volts on one pin and micro volts on the other.

Carrier is good, no modulation seen on either meter nor REA modulation monitor on my PC. I can usually listen to my modulation on the PC and now there is none. The mic in connector is stock and I did prove at one point during this awful day that I can feel 150 volts! Whether it's still there or not remains to be seen.

I was able to check the audio tubes other than the 6146 modulators. That's when I learned the plate cap wire on my Heathkit TC-2 tube tester was cut too short by someone somewhere along the line of ownership. Calling it a day now before I manage to break something else in my negative mood.

More to follow..................................

73
Jack
WA2OLZ

When you're up for it, try a simple test to see that the heaters of the audio tubes are lighting. Dim the room lights for easier viewing. Sometimes it takes a reseating of a tube to reestablish the connections when the contacts are tarnished.

Make sure the accessory plug is securely inserted in the back of the chassis. The audio filaments run through it. Do you see any resting current for the modulators? It should be between 50 and 70 mA.

If this bothers you you should find newer equipment.
You can not break something just by using different microphones.
Connection broken (solder joint), loose jack, dirty connection to something...

What are you going to do when a filter cap lets go or a tube fails?

Fix it - with help from the fine folks here on AMfone

I re-read the original post and noted that you said you don't get the satisfying think [sic] when squeezing the PTT. "Thunk", right? That's heard when the HV power supply is powered up, but if you don't hear that (or it's not the same) then it's possible that something with the supply or its load has changed.

Does the plate current still read between 300 and 330 mA when you key up?

No worries. We'll get this gal working again. It's just a matter of narrowing down the issue. Be glad you don't own a rig with a surface-mount CPU that hasn't been manufactured in 20 years!

Who are you calling "fine folks"?

Best thing about Valiants is plenty of room to put large parts.

RF Output is about 150W, the same as before. Loading is as before. Frequency is correct per my counter. Hear it in my receiver as expected.

Applying a 1000 Cycle tone to the autopatch input produces a clear tone on the output. Modulation meter reacts accordingly and signal looks clean on my monitor. The cheap Chinese signal generator I bought on a whim just paid off!

Those two points tell me I didn't break anything too badly.

Attaching a microphone to the two-pin jack on the apron results in a LOUD hum on transmit. Can see it on the monitor and I think I hear it on the receiver. Kind of hard to tell for sure. I've tried three different mics both with and without the W2IHY equalizer (I suspected the equalizer was the problem, but the symptom is the same with it out of the mix).

Either there is something amiss in the first audio stage or between the audio in jack and the amp. One curious measurement is on the mic jack. I see the 150V on one pin but can't read any voltage on the other. That could be cockpit or meter issues, however. To be honest, I've tried so many combinations today I don't recall what's what anymore. I've got to pick up some RCA jacks tomorrow and try going from the mic to the phone patch input.

There is still hope that I have not committed any major transgression.

73
Jack
WA2OLZ

Great news! It sounds like a connector issue now. The mic jack connection with the high (negative) voltage is the PTT. This gets grounded to transmit. The other is for mic audio and won't have voltage on it.

Does the hum go away when the Audio level is turned all the way down?

Take an ohmmeter and confirm that pressing the PTT switch on the mic causes a low resistance to appear between the shell of the mic plug and one of the pins.

It's also possible that the keying voltage is getting into the audio circuit. Do you get the hum if you use the manual transmit toggle switch to the right of the Audio control?

Maybe the key line got hooked to the audio line out of the audio stuff. Poof.

That's very much what I suspect happened as I was swapping stuff around. The question now becomes 'what went poof'?

Jack

Maybe nothing went poof. Do you have a microphone that can plug directly into the back of the transmitter? If so, try that to eliminate non-Valiant issues.

That's the plan. I need to pick up a couple of RCA plugs and give that a try. hopefully tomorrow night.

Small screwdriver into the jack and clip leads also work. Testing doesn't have to be fancy.

LOL - I suspect that's what I did wrong in the first place (-;

How are things getting connected to the two pin Amphenol microphone jack on the back? Does everything have that kind of plug or did you fabricate an adaptor?

I found several of the matching connectors on Flea-Bay when I first acquired the Valiant.

Check the external stuff to see if it still makes audio.

A mic into the phone patch input probably won't play well as it's fairly low impedance and requires more level than most mics can make.

My testing of a mike connector input is to turn up the audio gain a bit and, while holding a metal screwdriver and without touching your body to anything else (chassis, floor, pail of water, spittoon, etc.), touch the input lead, pin, etc. If you hear hum in the receiver, or meter swings up in the modulator position, you got audio.

Use the same method Pete. Do you draw arcs from the tank coil with a lead pencil too?
:) :o

Not recently, but I do use a NE-30 or a NE-40 neon lamp to detect RF in a tank coil and sometimes even a fluorescent tube.

Do you hang the tube on the antenna for your neighbors pleasure?

As a Novice, I tied two fluorescent tubes, one on each end of my 40 meter dipole. Great for CW work at night and was told it looked weird. After several visits from neighbors, my father ordered me to take them down.

As much as I enjoy scaring my neighbors with visions of UFOs surrounding my log periodic antenna.................back to our originally scheduled program:

We now have a 1KC audio signal going all the way from the two-pin audio input jack to the output. Yay! The issue then became no audio when speaking into the microphone. Who cares? The Valiant itself is out of its shell, but working. While it was unclothed I ordered a couple of 3B28 rectifiers to replace the mercury vapor 866 tubes. Why not? It was unclothed anyway anyway. That led to ordering a bunch of 6146 tubes. I figured get them while I can. I digress. The audio chain in the Valiant is alive and well. Not sure what changed, but it is what it is. Now I suspect I killed either a W2IHY 8-Band Equalizer and or my Kenwood MC-60A microphone. Using a backup EV 638 I now have normal audio through the rig, bypassing the equalizer. Being connector challenged, I can't tell if the mic or equalizer is bad, but we are getting there! The transmitter will remain out of its shell until I receive the 3B28s and then back into its case it goes.

Thanks to all for the support and tips. This has been a learning experience for me, not a bad thing. My intimate knowledge of the venerable Valiant is now greatly enhanced.

NB: the audio input pin on the two-pin connector may have been pushed in. Not sure, but I think I pushed it back out with the scope probe. That could explain a lot!

I took the case off my Valiant years ago.  There is no concern for TVI these days.  I rebuilt it with lots of mods, but left the 866s as I must admit I like the purple glowage. ::)

I actually did create TVI a few years back with a 6M Gonset.  Had to add the missing LPF.  So THAT was why it was there.

Pete - LMAO with your 40 meter dipole story!

~ps

I also like the magic purple glow, but the inevitability of flashback and my relationship with Murphy dictated the change  ;D