Viking Valiant

[n4wc]

Loaded up the "stock" Valiant this morning.  All was well for about 10 minutes then I heard a poof and no power out.  No grid drive.  High voltage good ie MV glow.  OSC and Buffer good on the meter.  The plate current was low, so I assume the clamper was doing its job.  I am looking for suggestions before I put it on its side.  I don't think I have another 5763.  Is this the most logical problem?

Thanks   Bill

[WQ9E]

Bill,

It could very well be the Drive pot.  Look under DX-100 on the mods part of AMfone if you want to replace it with a TV Horizontal output transistor and low power regular pot since the originals are expensive/difficult to source.
Also take a look at C96,97 as they can be troublesome.

[Ed/KB1HYS]

Just for grins, check the small choke at the base of the plate choke. Looks like a long resistor.

When it goes, it makes a puff of magic smoke and no output.

[xe1yzy]

Bill,

       Also could be a good idea check the auxiliary coupling switch, Is a comon source of troubles when you can load the transmitter.

Good Luck!

Pedro XE1YZY

[n4wc]

I appreciate the inputs.  Drive pot problem here.  Looking into the series pass device idea.  I do have a sort of junk Viking II with a good drive pot; just need to check the values.
73 Bill

[WQ9E]

Bill,

Values are the same, of course your Viking pot is also going to be similar vintage and subject to failure.

If you have not already done so, replace C33 (multiplier screen bypass) with a new capacitor since a short here would  take out the pot.

[W1AEX]

When I faced this problem with my Viking One back in the late 70's, Pete -W1VZR gave me this circuit. It has run perfectly since I installed it, using the same tubes the whole time. Just another option to look at. In the Valiant, of course, the 5763 would be present rather than the 6AQ5.

Good luck,

Rob W1AEX