The PHILCO Phorum
38-5 volume problem - Printable Version

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RE: 38-5 volume problem - Arran - 12-19-2014

(12-17-2014, 07:38 PM)r8i0 Wrote:  
(12-17-2014, 07:07 PM)Mike Wrote:  Welcome to phorum. Did you by chance get around to checking the grid cap leads as mentioned by Aaron?

Hi Mike
I cleaned the grid caps and the connectors and still have the problem. I Just replaced the 6f6 tubes again no solution.

Almost 30 years repairing radios and this is one of the toughest.
r8i0

It isn't just a matter of cleaning them, sometimes they need to have the joint re-soldered, the lead due to internal breakage, and the cap itself due to a deteriorating solder joint.
Regards
Arran

RE: 38-5 volume problem - r8i0 - 12-21-2014

    Bill, you've got a lot more experience than I do so I doubt I can help much, but I feel your pain.  I've got an 84B that has a similar volume jumping around problem that I've yet to diagnose.  I've prodded for loose components; looked for cold solder joints;  cleaned dirty pots and tube pins but haven't located
[/quote]

Good evening,
Earlier today I replaced the pair of 6f6 tubes with a pair of 6v6 tubes and the problem got worse. The bounce went crazy. Big highs and low lows. I am going to concentrate on the output for now and will report the results.
R8i0
[/quote]

Well, I think that I finally found the problem. I decided to replace ALL the resistors in the radio and found that in an earlier repair they put a .01 on the grid of the 6J5 and the schematic called for a 110mmf. I replaced this cap and the radio is playing at a nice steady volume for about 30 minutes now. I'll play it for another hour or so and if it is still good I'll call it done. I will check the alignment again and then put it back in the cabinet. I will then try to send a picture of it completed.
Thanks to all who helped with this fix. Merry Christmas.

RE: 38-5 volume problem - klondike98 - 12-21-2014

Congrats!! 
110pF.....0.01uF....someone missed a few decimal points on that conversion Icon_lol  Glad you found the problem.

RE: 38-5 volume problem - morzh - 12-21-2014

I wonder why the volume was bouncing....unless it was a phaseshift created by the cap since the triode is part of the AVC which is a neg. feedback so it got to oscillate....