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Viking Valant 2




 
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October 21, 2017, 10:41:12 PM *
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Author Topic: Viking Valant 2  (Read 417 times)
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KE7KPB
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« on: October 10, 2017, 07:24:13 PM »

I was doing a tuneup on the old girl and I had the the meter switch on plate. Hit the manual switch and the meter pegged and the front 866 started sparking. I then did a replacement of all of the electrolytic caps. Still have the issue.
i have not changed to 10k resister in the vfo as of yet. Would that be the cause? 
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DMOD
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« Reply #1 on: October 10, 2017, 08:03:32 PM »

Did you receive this unit recently or have had it for some time and it worked previously?

Remove the 6146's and test them in a conductance tube tester. You may have a shorted 6146 because you are drawing some major current.

Another problem in these rigs is the Clamp tube circuit V8; either the tube goes bad or this stage is misadjusted.

http://bama.edebris.com/manuals/johnson/valiant2/


Phil - AC0OB
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KE7KPB
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« Reply #2 on: October 10, 2017, 10:44:04 PM »

Thanks, I will check it out. I get to use my Hickok 539c. I will keep you informed.
The transmitter has sat for 50 years so that is why the cap replacement. It did tune up for a short time.
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N1BCG
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« Reply #3 on: October 10, 2017, 11:02:07 PM »

One safe way to begin the testing is to measure the resistance of the HV supply (but first with the rig off, unplugged, and a shorting wire connected between the plates of the rectifier tubes and chassis for 10 seconds).

After it's been assured that any stored voltages have been removed, check that and the resistance between the RF 6146 plates and the chassis.

The result should indicate if you have a supply failure such as shorted cap, broken insulation, bad transformer winding, etc.  If it looks reasonable, assure that you have proper bias at the RF 6146 grids (-70 VDC). This can be done without turning on the HV supply.
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w8khk
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« Reply #4 on: October 11, 2017, 02:45:22 AM »

One safe way to begin the testing is to measure the resistance of the HV supply (but first with the rig off, unplugged, and a shorting wire connected between the plates of the rectifier tubes and chassis for 10 seconds)
I am not sure it would help to short the plates to ground.  More effective to short the filaments of the 866s to ground.
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N1BCG
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« Reply #5 on: October 11, 2017, 07:26:23 AM »

More effective to short the filaments of the 866s to ground.

You are absolutely correct, and it demonstrates why cross-checks from a separate set of eyes are invaluable. Shorting the plate caps of either the RF or AF 6146 tubes to the chassis would also work.

The resistance should be about 40k Ohms, which is the sum of the voltage equalizing resistors across the HV caps.
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k7pp
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« Reply #6 on: October 11, 2017, 03:20:14 PM »

Might I suggest that shorting the plates of the 6146 finals to ground to discharge the filter caps might blow your plate choke wide open.
Shorting the modulator tube plates to ground risks your modulator iron as well.
Keep in mind that there are three power supplies in the Val.   High voltage,  low voltage and the bias supply.
Might I recommend locating the individual filters in the transmitter and shorting them directly to ground.   
Better safe than sorry???   Just sayin'.
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KE7KPB
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« Reply #7 on: October 11, 2017, 06:55:49 PM »

The transmitter has never been touched. I did do a complete electrolytic capacitor replacement using 105c caps. i even watched the one where the + side was going to chassis. The 866 tube in the front was the one doing the sparking and the meter was on plate and it wanted to bury its self. I'm going to pull the 6146A out and test them on my 539C.
This is great information now to print and go to work. I will keep you informed as to what I find. Cheesy
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WD5JKO
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« Reply #8 on: October 11, 2017, 07:14:21 PM »


The 866's might be bad, or at least one of them.

There are several SS replacements on Epay right now. Look for 1N2637.

Jim
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