Sound Problem

[jr_tech]

When the sound fades out, are the heaters of the audio output and other audio tubes lit up? Perhaps cleaning the pins would help?
jr

[Zenith26kc20]

Check the audio tubes for grid leakage. One of my TS-18 motorolas did that and it was one of the audio tubes.

[VA561]

Based on the schematic which tunes do you think would be the most likely suspects?

[Don Lindsly]

6AU6, 6T8 and 6W6 are the tubes most likely to affect sound.

Also try slightly rocking or tapping the sound discriminator transformer, 32-4450 or 32-4631, if I recall.

[Phil Nelson]

Originally Posted by jr_tech

Perhaps cleaning the pins would help

Cleaning tube pins and sockets is a good thing to do at the beginning of every restoration:

http://www.antiqueradio.org/FirstStepsInRestoration.htm

Phil Nelson

[Mal Fuller]

"Fading away" suggests a tube filament cooling off. I'd check the ground connection to the audio output tube's filament and, if applicable, the ground on the pc board upon which the audio output tube is located.

[old_coot88]

Originally Posted by Mal Fuller

"Fading away" suggests a tube filament cooling off.

..Or a rare possibly is a floating grid condition, ie., an open in the DC return path to ground. That would allow the tube to self-bias by space charge, eventually cutting it off.

[VA561]

I am crossing my fingers but it appears as though the culprit was a bad 6T8 tube (FM DET/ 1ST AUD) on the schematic. I replaced it with a good RCA tube and so far it is working fine. As usual, there is always a gold mine of great advice from everyone who responds on this forum. To everyone who took the time to try and help, thank you.