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Author Topic: Viking Valiant Questions  (Read 8592 times)
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K9AAL
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« on: April 04, 2009, 10:50:48 PM »

I have a couple of questions about my Viking Valiant:

     Running on AM at plate current of 330 mA, the transmitter down-modulates.  If I reduce the drive and run at about 200 mA plate current, it up-modulates, but at end of transmission, I get arcing between the moveable contacts of mode switch SW4B (B+ and screen of modulator tubes).  Arcing does not occur (so far) at full power.

     Tranmitted note on CW is slightly rough and has minimal chirp when running at plate current of 400 mA.  Both seem slightly less noticeable at plate current of 300mA.  I also get a change in frequency of about 200 Hz during tune up on CW--frequency increases.  HV filter caps and choke have been replaced.

     Incidentally, the neutralizing cap is at maximum capacity (fully meshed).

     I have weekends (sometimes) to work on this project, so may be slow to implement suggestions!!

Thanks, George





     


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w3jn
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« Reply #1 on: April 04, 2009, 11:33:02 PM »

I never load my valiant to the recommended 330 mA.  The mudulator's just not stout enough.  Better is about 280 mA or so.

Some things to look at:

1)  The Junkston meter shunts are a well known source of trouble.  Check the meter accuracy with a meter of known accuracy.
2)  Chernobyl resistor in the VFO compartment.  A must-do.
3)  Could be weak rectifiers, weak mudulators, screen resistors out of tolerance, etc.  Check voltages.
4)  The arc on unkey problem - you now have a small carbon trace between those switch contacts which needs to be cleaned out.  Most likely because you're running less plate current the HV is quite a bit more, probably just enough to cause the arcing.  Again this points to rectifiers sagging under load.

I'd pitch those 866s as far as I possibly could and replace 'em with 3B28 xenons or solid state 'em.  The latter has the advantage of getting rid of the heat source and 15 watts or so of power draw in addition to saving your power tranny from merc vapor toob flashover.. 

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WQ9E
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« Reply #2 on: April 04, 2009, 11:33:09 PM »

George,

First, be very careful when turning the Valiant over to work on it as the coupler in the VFO drive is easily broken.  It is best to loosen the set screws to avoid this from happening since this is a non-standard part with different sized input and output shaft sizes.  What happens is the heavy weight of the Valiant tries to flex the front panel when it is resting upside down and the coupler tries to help the panel resist this flexing and the coupler loses every time.

Also, if this is an early Valiant check the cathode wiring from the LV transformer to the 866A sockets.  Early Valiants were built with regular hook-up wire for these leads and it isn't sufficient for the voltage (5 volt filament plus rectified HV) that appears on them.  Either replace or sleeve to prevent breakdown to chassis and loss of LV transformer.  If you are running SS replacements for the HV rectifiers then disconnect and tape these transformer leads at the tube socket.

For the downward modulation:  Make sure your screen and bias voltages are set properly.  Are you running MV or solid state rectifiers?  If you are running the mercury vapor (866A) still you may have one or both rectifiers weak.  It could also be insufficient grid drive; kit built Valiants in particular often have very inaccurate meter shunts.  It should not downward modulate at rated power.  I have never run into arcing problems on the mode switch but running at reduced RF input you probably have excessive audio input causing the arcing (due to a transient when unkeying).

There will be some chirp on the highest bands but it should be very clean on 160, 80, and 20.  If you have chirp on 40 it is probably due to RF getting in to the VFO and the basic cure for that is properly grounding the VFO input shaft.  You may need to also adjust the keyer setting.  If the note is rough at all power levels (or in spot) suspect heater/cathode leakage in the VFO and/or keyer tube.  If the bias filter caps have not already been replaced they should be.  If you have not replaced the 18K dropping resistor in the VFO (it feeds the VR tube) you should do so, 18K is the correct value but it needs to be a higher wattage unit than the original.  You can replace it through accessing the left side of the VFO (your left looking from the front of the transmitter towards the back).  There is no need to completely remove the VFO for this procedure.

The neutralizing cap should not be at full mesh normally.  Check the lead dress in wiring if this is a kit built unit; also did someone replace C96/C97 with different value units?  Otherwise I would suspect a problem with a tube in the final section.

Finally, if you find low output and/or odd tuning only on 160 then check the value of the DC blocking/final coupling cap.  Early Valiants were built with 500 pf which is too small, later ones were increase to 2000pf or greater.  If you run into odd tuning on all bands take a close look at the fixed loading caps.  The "turnstyle" unit is often bad.

Good luck with your Valiant!
Rodger WQ9E
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Rodger WQ9E
K9AAL
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« Reply #3 on: April 18, 2009, 06:06:25 PM »

Finally have had a chance to work on the Valiant. 

Checked the screen voltage on the final--was about 265 volts and the bias was -83 volts.  Checked the clamper and it read 10mA.  I also checked the plate meter and it was "accurate".  I reduced the screen voltage with the clamper adjustment to 155 volts, and of course had no measurable plate current.  However, with that adjustment, no change in output, and with key down, screen voltage went to 194 volts, bias to -77 volts.  Tried it on AM and at 300mA plate current, now have upward modulation.  I don't have a scope, so I guess I don't know how it sounds. I cleaned the carbon track on the mode switch where it had been arcing, and so far no arcing!

Also, checked the keyer adjustment with respect to chirp, and no help.  It is hard to say, but I think the chirp is only on 40 meters.  However, the rough note is on all bands, and changing the keyer tube made no difference.  I am about to be sure the VFO coupler shaft is adequaetly grounded (not sure what the best way to correct that is if it isn't grounded well) and change the VFO tube out and see what happens to the tone and chirp.

I have SS rectifiers, not the 866's and all the filter caps have been replaced.  This is a factory built transmitter.

Any further suggestions would be appreciated, as I am pretty much a beginner at this!

Thanks, George, K9AAL
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WQ9E
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« Reply #4 on: April 18, 2009, 06:47:57 PM »

If the chirp is only on 40, it is due to RF getting back into the VFO.  Ground the shaft going into the VFO .  Also, some runs of the Valiant and Ranger have a long open slot in the front of the VFO houseing where the shaft enters so you may need to shield that (foil tape works fine).  You can use flexible braid or a spring contact to ground the input shaft.

Before you go into the VFO checking for the rough note, plug a crystal in and see if the note is also bad on crystal control.  If it is OK on crystal then you probably have heater/cathode leakage in the VFO tube.  If it is also bad on crystal you probably have another defective tube in the RF driver chain; however try replacing the clamp tube first as that caused a rough note on my Ranger when it had heater/cathode leakage.

Rodger WQ9E
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Rodger WQ9E
K9AAL
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« Reply #5 on: April 19, 2009, 03:55:30 PM »

I changed out the clamper tube, readjusted the screen voltage to 155 volts, and things really sounded better.  VFO keyed in zero position sounded pretty clean and comparing the "note" of the fully loaded Valiant to the side tone on my Kenwood TS-850, the valiant sounded minimally rougher than the side tone.  I changed out all the tubes up to the final, without any other appreciable change except for the clamper tube.  One other thing I noted, is that in the past, before adjusting the screen voltage down and replacing the clamper tube is that the transmitter used to change frequency as it was tuned--doesn't seem to do that anymore.

I also tried to use a crystal, and it only oscillated intermittently--didn't matter which 6CL6 I used.

I guess I can leave well enough alone, now, unless there is any problem with the fact that with the screen voltage on the final at 155Volts, I don't get the 10 mA of plate current.  Any ideas on that? 

Thanks, George
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WQ9E
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« Reply #6 on: April 19, 2009, 04:05:40 PM »

George,

The 10 ma value is set with the clamper adjustment R-13 and this is the target value with the Valiant set for crystal control with NO crystal in the selected position with the transmitter on and keyed.  Less than 10 mils "clamped" current is fine as long as you can still load the final to normal input.  So as long as the clamped current (in transmit but with no excitation) is low and the transmitter develops normal power everything is fine.

If a number of your crystals are not oscillating, check the keyer tube circuit since it also keys the crystal oscillator.

Enjoy the Valiant!

Rodger WQ9E

 
I guess I can leave well enough alone, now, unless there is any problem with the fact that with the screen voltage on the final at 155Volts, I don't get the 10 mA of plate current.  Any ideas on that? 

Thanks, George
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Rodger WQ9E
K9AAL
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« Reply #7 on: April 19, 2009, 04:30:16 PM »

I only have two crystals and one is not very repsonsive in another transmitter on 40 meters. The second one is 1.810 MHz, and has been lying around for about 40 years.  It oscillated briefly and then stopped!  I will see if I can find any other crystals around--I think I loaned a good one one to a friend so if I can track it down, that will be the next test--but in the meantime I can run on the VFO.

Regarding the screen voltage, I reduced it from well over 200 volts to 155 using R-13, and when I had set the plate current at 10 mA that resulted in a screen voltage of about 265 volts.  Makes me wonder about the meter--although at higher currents it is pretty accurate. 

I really appreciate the help on this--it seems I may actually get on the air with it pretty soon!!

George

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