R390a DOA

[Detroit47]

I went to use my 390 today but.........It don't work the s meter is working but no audio. I’m not sure but I recall hearing something about an infamous ballast tube. I have it in a rack so just getting at it is a chore.

73 N8QPC

[flintstone mop]

S meter working is a good thing... The ballast tube is working. Could be power supply problems on the audio module. The are capacitors on that module that distribute B+ to the rest of the set. If this is the first time something went wrong, it might be a good time to replace those caps. It made my radio run like new with all of the B+ back to spec.
You might get lucky and it's just a tube.

Fred

[W3SLK]

I agree with Fred and to take it one further I'd put a .1ufd cap of the diode output into an audio amp. This would tell you if its the audio stage or before the detector. Also, don't be afraid to check those antenna relays. They are notorious for hanging up.

[flintstone mop]

I agree with Fred and to take it one further I'd put a .1ufd cap of the diode output into an audio amp. This would tell you if its the audio stage or before the detector. Also, don't be afraid to check those antenna relays. They are notorious for hanging up.

YUP Mike(y) that starts to narrow down the fault.
It's truly amazing how those poor receivers survived in a typical comm center. This was before it was affordable to air condition a space just for electronics. Racks of R390's the SSB converters to recover 4 channels of voice or many channels of teletype with another rack of tubes to convert the audio tones to DC. geesh!
4 each 3kc slots of audio. I think a teletype terminal could demodulate ?? teletype signals............here is a link to something I remember seeing in Ft Monmouth
http://www.navy-radio.com/rtty-mux-fgc5.htm

Fred

[W2PFY]

The r390A that i have does not use the ballast tube. it is jumped out. the two tubes in the PTO have been changed to the 12 volt version thereby eliminating the need for the ballast tube.