My good 'ole Valiant II, no grid current all of the sudden?

[N5DMC]

Hello fellow AM'ers

Well yesterday I was in the middle of a QSO on 80m, not a fuse blower by any means and all of the sudden I see my plate current was sagging down to nothing. I looked more closely to find also that the drive control was cold. No Grid Drive on any band. Valiant II operators know what I mean when I say that the aluminum knob was all of the sudden cold. The R-51 (25K pot) has been upgraded at some point to a larger unit, and it tests of with the ohm meter. also V-3 & 4 test OK on my Hickock 800 well into the green. No spot currently, not as normal on the receiver is heard either, but it was there just before. I think this is my best clue, something in the VFO, the oscillator is showing good current 22mA, buffer about 14mA. Socket resistance test could be next.

So as I dig into this issue, I wanted too start another Valiant thread as I have not found anything exact like this issue. Not 100% sure of testing what voltages where. I am good with open & hot chassis with H.V. but if anyone knows of some quick check outs that I can preform, let me know.

Some history on this chassis....this Valiant II is in museum like condition. It worked 100% for 6 months now, only 60 watts carrier at the Johnson recommended settings, per the manual. The resting current is ~50mA, so I believe the bias is OK, low output could be the so-so output 6146s tubes which test borderline as of last night just after the problem occurred. All the electrolytics have been changed out 6 months ago. I did notice that the VR tubes light with out any transmit in the AM mode position, nor is there any plate current. Been also been following N2LK's threads, really good stuff.

More soon. Thx in advance for your expert advice. This is my dream rig, thanks to R.L. Howard WC5E

Best,
Doug
N5DMC

[N5DMC]

Testing V-8 6AQ5 looks real good in the tester. I should mention that went the issue happened, it was a slow decline. The TX relay is not stuck. The VR tube light simply when it's placed in the AM mode.

On to more t-shooting, may yank the cover off. But WC5E did install a sweet hinged top cover that is real handy at the present.

Best,
N5DMC

[N8ETQ]

Hey Doug,

             Well that sux... See if you can hear the VFO
on the shack RX, Could be the "R" in the VFO that feeds
LV to the OA2 in there.. Chernobyl Resistor it's been
Glossed...

            A real PIA to get to...

GL

/Dan

[N5DMC]

Thanks Dan for the reply,

EDIT I did notice that the VR tubes light with out any transmit in the AM mode position This happens only during xmit in AM which is normal.

No spot. Actually I was checking my tune at the time I realized what was happening. Had the spot & then a slow fade to nothing...later checking I found I had no grid drive. Been operating this 'ole honey with velvet gloves. Never doing things like adjusting the coupling while xmitting, etc.

Well the 18K resistor looks new, and the solder does too, to the socket of V2 across R3 measures 18k exactly. Starting to trace now. I'll let you all know what I find.

73's
Doug
N5DMC

[N1BCG]

With the rig set to generate a spot frequency, check the various meter readings for change. You mentioned that you get a signal then it fades out, right?  The meter selector switch can help determine at what stage the failure is occurring.

The drive control being cold is odd. Those usually throw off a lot of heat so you may have a LVB+ issue. Perhaps the rectifier is going bad (check that the heater is glowing).

[N5DMC]

Yes, it did generate a spot signal, now at this point nothing. LV looks good at ~300VDC. Thinking the issue inside the VFO, Will verify by looking at J-10 for the external VFO signal at this point with a DVM, in the SSB position. Will ck back tomorrow, noonish.

Many thx guys

73's
Doug
N5DMC

[N1BCG]

Try several bands. The Oscillator runs straight through on 160 and 40. All other bands use doubling, etc. This could also be caused by a poor switch connection since the rotary switch contacts can get badly tarnished. I use a pencil tip eraser to clean the rotating metal surfaces. Follow that with isopropyl alcohol applied with cotton swabs.

[N5DMC]

Thanks N1BCG,

On all bands. Last night, I was busy tracing out everything, well as best as I could. Tested the 6AU6 in the VFO on the Hickock, it was OK. OA2, who knows. I have a spare rig, so I can always pull that one and try it. I need to go over the low voltage readings again. As far as the rotary contacts go, being a part time jeweler, I always look for overheated contacts. Good deflection from integration with the wiper. So far all looks good. Putting the curl back in them is a trick to getting good contact, so far with this rig not too bad, but the ohm meter won't lie. More checking needed.

I use these "high tech" Q-tips, called "eye tees", they have a pencil like hard tip & their wrapped pretty tight, so not to hang up on sharp edges. The brand is by Fran Wilson. www.franwilson.com  fyi. I keep telling myself, it's got to be something simple Hi!

I'll be back at it later this afternoon & will be checking in here. Thanks everyone. Still following N2LK's threads too. Good stuff there.

Best,
Doug
N5DMC

[N1BCG]

Does the OSC position of the Meter switch show anything when Zero (Spot) is selected on the Oscillator switch? Technically this only shows that V2, the crystal oscillator/buffer, is drawing current. Placing a crystal, if you have one, in either crystal socket and selecting it with the Osc switch would test V2 and all circuits past that to the finals. You'd have to set the Mode switch to CW in order to run the crystal oscillator without actually transmitting.

If that works then the problem is with the VFO (V1). You mentioned that R3 the 18k resistor tested ok, but if possible, test the voltage at both ends with the spot function (Zero) active.

You should see LVB+ (~300V) on one side and the 0A2 regulated voltage (150V) on the other. Resistors can change value when hot (and that one roasts).

Another point to test is the cathode circuit of V1 at L19 or contact 11 of the Oscillator switch. The voltage should go low when the oscillator is operating.

[N5DMC]

You should see LVB+ (~300V) on one side and the 0A2 regulated voltage (150V) on the other. Measured to ground I presume? Can't wait to dig back into this in a couple of hours

Best
Doug
N5DMC

[N5DMC]

From N1BCG's recommendations, I have completed the following tests with readings:

R-3 does indeed have 375vdc on one side & 150vdc on the other (pin 5 (OA2).

Took 3 readings; On pin 11 of the Oscillator switch and L-19 (both sides,) all the same, goes from 56 mvdc (vfo position) to zero (in the zero position), checked this with 2 separate known good fluke meters. During this test, the oscillator current drops about 20% in the zero position, from 22 to 18 in AM mode only (doubled reading, bottom scale).

Not sure if the oscillator is operating, no spot at all. Normally I never use the "Zero" position ever, on the Oscillator rotary switch to spot on my receiver, it works well using the CW position.

The buffer reading has always seem low, now lower than normal; only 3 on the scale (doubled bottom scale =6)

Looking for the ~300vdc LV at the bottom of R-51 (drive pot) and found indeed 375vdc across it. But the pot seems a little funky, exactly like the thought of changing out. Sub panels grrr... reads 25kohm, however the span on my simpson 270 is not very linear. It's 25k, but the center wiper's readout is not smooth, as so is the feel. Pull the coupling trim shaft to get to the right angle bracket nut underneath. Hope I have a pot. The transistor/FET mod is looking good now!

More soon....Doug

[N1BCG]

Normally I never use the "Zero" position ever, on the Oscillator rotary switch to spot on my receiver, it works well using the CW position.

The oscillator works fine when the Mode switch is set to CW but not when it's set to AM and the Oscillator switch set to Zero?

[N5DMC]

N1BCG,

The oscillator works fine when the Mode switch is set to CW but not when it's set to AM and the Oscillator switch set to Zero?  Will answer that when (and if~) I can get through this next hurtle Hi.

Issue resolved. It was the drive pot. Installed a new one I had, 4 watt & I got drive once again.

Now it's doing something very weird. It keys all by it's self with the microphone plugged in, with 2 different mics. After a cold warm up, within ~ 10 seconds, when it's warm after pwr off within a couple of seconds. Found a 1 watt 47K resistor broken at the key adjustment. This is a kit build chassis. Had to replace the resistor, R-42. Tested, same thing. Looked at the R-39 (100k pot) VFO Keying Adj, found it open, replaced that, same deal with any adjustment. It's ground side opened, was set to 75K, and preset the replacement. No adjustment full ccw or cw will change anything.  Now I want to pull V11, the 12AU7 to see if is that tube doing the after warm up ghost keying but no sure if I should try doing this. I also need to check C-63 bypass cap at the mic connector to see if it's leaky. Funny that the TX relay pulls in only when all the filaments are warm. Placing a wire to pin 2 (the PTT) does trigger the TX relay normally, and again, w/o anything plugged into the mic connector, nothing happens. But with 2 different microphones that are good (tested w/ an ohm meter to verify) they both trip the TX relay...after a delay on cold power on. Need to look at R-40, the 1 Meg wiper resistor next.

The transmitter does seem to work normally however in CW.

Thanks for all your help, everyone. I'm going to take a break and get back to it in a short bit.

Doug

[N1BCG]

The keying voltage comes from the LVB+ so if the keying line is shorted to ground, the relay will close when the 5V4 rectifier starts to conduct.

It's possible that there's a short at the mic connector.

What's the Mic connector Pin 2 resistance to ground with one of the regulator tubes removed and a mic connected? It should be infinite...

[N5DMC]

It is infinite, with the mic plugged in (w/o the one VR tube). I can see the mic PTT looking correct with the power off, with it on... watching the DC voltage rise just before the ghost trigger on the same pin 2. With the VR tubes installed, the coil resistance can be seen.

Tried the parallel 1/4" stereo plug wired in next to the 2 pin mic plug, same deal.

Q: What does the "VFO Keyer Adjust" do?

...well it works for some reason, cycled the 1/4" plug a few times and everything seems to work, also I did plug in the mic w/ the new type plug while it was on, and since then.....working. This is a kit build. the workmanship tells alot, screws on all the sockets.

I may post again with the spot working hopefully, all hooked up with the HRO 50T like it was andwill hopefully give the thumbs up. Thinking of trading everything for a Collins Transceiver.

More by tomorrow at the latest.

Thanks again everyone, especially N1BCG

Doug
N5DMC

[N1BCG]

That bypass cap and the mic connector is def a suspect.

1) What does the "VFO Keyer Adjust" do?

2) Thinking of trading everything for a Collins Transceiver.

3) Thanks again everyone, especially N1BCG

1) The keyer adjustment controls the triggering threshold of the oscillator. Not sure if that's a reasonable answer but I can elaborate if ness.

2) Come on now, after all this? You'll love this setup again soon

3) My Valiant ran me through 4 months of sparks, smoke, fire, and burning smells. I swore after that that nobody should have to slog though that alone. After that, it was amazing how many Valiants came through here with ailments, but none insurmountable. Hey, look at it this way.... no out of production microprocessors or surface mount components! :-)

[N5DMC]

Thanks...

Setting the bian now at -69 Vdc, but still suffering from low output. Gained 20mA Ip at -58 Vdc. All the coupling caps are good, at least testing w/ a Beckman cap checker as alright, nothing shorted in any band at the SO-239 to gnd.

Set the RF & Mod Bias, Clamper. Neutralization was already done a couple of months ago.

Wondering how I could fudge something to get more Po. Will land myself a set of 3 new 6146 at the Belton, TX swapmet.
Next the resting current, which was OK.

No uP love here. There only as good as their last firmware update Hi.

Ok time to button her up & cross my fingers. The harness is right against the rear inside, so I need to shorten the 1/2" 1/4-20 screws.

More soon from Valiant Boulevard~

Doug
N5DMC