Valiant Zorch - What's the Story?

[W1UJR]

My troublesome Valiant has once again lived up to its name.
Guys, I'm puzzled here, stumped really.

This unit has had the audio modified by W1ZVR a few years back.
What would cause the resistor in series with one of the modulator plate leads to burn up?

Tube bias was correct, the unit was functioning well, was in a QSO with VE9AT when it happened, then zorch.

Suggestions, thoughts, etc?

Audio as follows:
12AU7 is the first stage of audio, the second half of the 12AU7 is the next audio stage, then a 6C4 and finally a 12BH7 to the stock driver transformer has been cross laminated, still driving 6146s.

[Pete, WA2CWA]

It might be helpful for brain pondering, to describe the audio mods that were done. Still using the 6146's as modulators, new mod transformer, feedback, etc.

Do you know what the mod. current was doing just before failure? Checked the suspect tube?

We need more info?

[Jim, W5JO]

As Pete says, check the 6146s.  Got a tube checker that will do 6146s?  Look for a shorted screen in one or G1 to Cathode. 

[W2VW]

Might try replacing both resistors and including some little ferrite beads on the plate leads.

[kc2ifr]

I think those resistors are used as fuses and/or supressors......but cant remember. I replaced the ones in my Valiant and had no more problems. One thing bad about those resistors is that if one opens......u might lose the screen in that toob. That happened to me.

[w3jn]

Look for a parasitic in the audio.