38-5 volume problem - Printable Version
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+--- Thread: 38-5 volume problem (/showthread.php?tid=11172)
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38-5 volume problem - r8i0 - 12-14-2014
I have almost completed the restoration of a Philco 38-5 big beast and am having a volume problem. The volume seems to bounce up and down and I can't figure the cause. I have already installed new caps and tested resistors and also have substituted all the tubes with no help. The radio plays great with tremendous volume and has been aligned already. The VC has been substituted as well.
Any ideas? It does this randomly.
RE: 38-5 volume problem - jerryhawthorne - 12-15-2014
Perhaps a good time to clean tube pins and sockets well?
Jerry
RE: 38-5 volume problem - Arran - 12-15-2014
Sometimes testing resistors is not often good enough, I would replace the plate resistor on the first audio tube. The next thing to look into are the grid cap leads, on the first audio tube and sometimes the first detector tube or RF amplifier tubes, it may also be a grid cap itself, failing solder joint. Dirty tube sockets can also cause problems, although not usually with octals or the old six and seven pin tubes in an AC set.
Regards
Arran
RE: 38-5 volume problem - r8i0 - 12-15-2014
Thanks for the suggestions. I am new to this phorum but have been reading the threads off an on for years. This volume problem has had me stumped so I figured it was time for the experts. I will follow the ideas given in the next day or so and will follow up and let everyone how it turned out.
Again.
Thanks,
RE: 38-5 volume problem - r8i0 - 12-17-2014
(12-15-2014, 08:45 AM)r8i0 Wrote: Thanks for the suggestions. I am new to this phorum but have been reading the threads off an on for years. This volume problem has had me stumped so I figured it was time for the experts. I will follow the ideas given in the next day or so and will follow up and let everyone how it turned out.
Again.
Thanks,
RE: 38-5 volume problem - r8i0 - 12-17-2014
HI all,
Thanks for the suggestions on the bouncing volume on my 38-5. I cleaned the pins and sockets of all 8 tubes and it did not help, I then replaced the plate resistor of the output tunes and still not help. Any other suggestions? This is a beautiful radio and I really don't want to give up on it. Any thoughts would be appreciated.
r8i0
RE: 38-5 volume problem - klondike98 - 12-17-2014
How about some deoxit squirted in the volume pot #44 ? (and welcome to the Phorum!)
RE: 38-5 volume problem - r8i0 - 12-17-2014
I deoxit-ed it and the problem is still there. I am going to replace the output tubes and see if that changes things.
r8i0
Thanks for the welcome and Merry Christmas to all.
RE: 38-5 volume problem - KCMike - 12-17-2014
Welcome to phorum. Did you by chance get around to checking the grid cap leads as mentioned by Aaron?
RE: 38-5 volume problem - r8i0 - 12-17-2014
(12-17-2014, 06:07 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
RE: 38-5 volume problem - KCMike - 12-17-2014
Wish I could offer more advice but I'm a rookie 2yrs in the hobby.
Someone here will probably have some more ideas on what you might check.
RE: 38-5 volume problem - jerryhawthorne - 12-18-2014
Any chance you have an O'scope? Would be useful in monitoring signal at various points and seeing where the level is jumping around. Monitoring plate voltages with a meter might also provide useful information.
Tough problems and good luck.
Jerry
RE: 38-5 volume problem - r8i0 - 12-18-2014
HI Jerry,
I do not have an O'scope. I have never had the need to use one. Sorry.....
Bill
RE: 38-5 volume problem - klondike98 - 12-18-2014
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 the source.
RE: 38-5 volume problem - r8i0 - 12-18-2014
(12-18-2014, 10:05 PM)klondike98 Wrote: 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
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