JOHNSON VIKING II issue

[Crambone]

Ahh.. If you have a carrier, the 6146 tubes will not be the focus of an audio problem. Especially a "no audio" problem.

The modulator plate current is the key hint here. Until the negative grid-bias voltage on pin 3 of the two 807 tubes comes down you won't have modulator plate current, or audio.

Leads me also to wonder how strong the 807 modulator tubes are. But until you can get a plate-current reading with no mike audio there's no good way to tell without a tube tester old enough to test them.

Really makes it sound as if R15 has gone bad. Maybe?

Or maybe the two 807 tubes are just flat as a pancake.

73

1) Im seeing -37.7Vdc on Pin 3 of both 807's
2) R15 tested good at 1.6K but I changed it anyway.
3)I tested the 807's with a Precision 920 and they show strong although I know its not the best tester its all I had.
4) I did find R13 the adjustable resistor to be bad, ordered from Mouser and will update.
5) Anything I should be concerned with that may have made R13 go bad?

 

[nomadradio]

R13? Good question. Don't remember variable screen-grid voltage on the modulator tubes in later model Johnson transmitters. That's what R13 does. Could have just worn out. Or could have been damaged by a bad 807 tube some time or another in the last 60 years.

I'd have to go back to the manual to see what voltage you should see on pin 2, the screen grid on the 807 tubes. If it's too low you won't see plate current on the modulator.

73