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 Post subject: 1931 Philco 370 volume erratic
PostPosted: May Sat 23, 2020 3:32 am 
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Joined: May Wed 13, 2020 2:57 am
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Location: Oregon
Everyone,

I recently got a 370 Lazyboy and it has a bit of a problem. I know that these have an unusual volume control that works on the antenna and tube bias and tends to be finicky, but I think something is different here...

The Symptoms: The radio will suddenly drop the volume into the core of the earth even when listening to a strong and consistent signal. This includes static and radio noise. It all drops. This isn't a case of late night fade in/out. It seems to happen more often if there is a sudden loud part or big pop from a noisy signal, but it can happen for no reason. Adjusting the volume up can sometimes bring it back (and then it will be too loud) and then you adjust back down. It might stay that way for a while, or just long enough for you to comfortably sit down away from the radio. If it remains quiet when you max the volume (though perhaps at a listenable volume) you can be sure that it is going to blast you out of the room at some point when it decides to go back to where it should.

The odd thing: If I reach under the radio and touch the metal bottom of the chassis, the volume goes back to where it should be. Sometimes that fixes it for a while, other times it drops back down as soon as I remove my finger or hand. Also, I did something silly and attached a piece of tape to the bottom of the chassis and sometimes pulling on it does the same thing. All this happens regardless of whether a ground cable is attached.

For a few days, the radio seemed to be fairly volume stable, but it has been troublesome lately. It makes late night listening frustrating to say the least!

Any suggestions? I have a hard time thinking that this is standard behavior. Can you imagine taking home your radio from the store, setting it down by your most comfortable chair, and having to get up and do an awkward reach to make the volume work again every 2 minutes?

Thanks for the help!


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Sat 23, 2020 9:11 pm 
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Joined: Jul Sat 25, 2015 11:30 pm
Posts: 94
Location: Cookeville, Tennessee
Sounds to me that you may have a dirty volume control. Try to work it back-and-forth after squirting in some tuner cleaner (with the AC disconnected) numerous times. Those old potentiometer controls tend to corrode and tarnish internally and a become unstable and the resistance changes as a result.


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Sat 23, 2020 11:50 pm 
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Location: Oregon
WA2SFT wrote:
Sounds to me that you may have a dirty volume control. Try to work it back-and-forth after squirting in some tuner cleaner (with the AC disconnected) numerous times. Those old potentiometer controls tend to corrode and tarnish internally and a become unstable and the resistance changes as a result.


I have done a ton of that so far. A lot of working and a lot of contact cleaner. I still don't know why touching the bottom of the chassis returns the volume to normal. Sometimes for a short time, sometimes longer.


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Sun 24, 2020 6:17 am 
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Location: Oregon
I'm wondering if the issues noted in this thread pertain to my situation:

https://antiqueradios.com/forums/viewto ... 6#p3015086


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Mon 25, 2020 12:12 am 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
Presumably this set uses tubes that have grid caps. These caps often develop continuity problems due to solder shearing. This gives symptoms such as those you are describing- sudden loss of volume, recovery caused by seemingly unrelated "adjustments" to the set such as touching the volume control or any part on the chassis. If you have spare tubes you might try swapping them out with those in the radio one at a time to see if the problem changes.


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Mon 25, 2020 5:11 am 
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lorenz200w wrote:
Presumably this set uses tubes that have grid caps. These caps often develop continuity problems due to solder shearing. This gives symptoms such as those you are describing- sudden loss of volume, recovery caused by seemingly unrelated "adjustments" to the set such as touching the volume control or any part on the chassis. If you have spare tubes you might try swapping them out with those in the radio one at a time to see if the problem changes.



I could give that a try. I'll need to order some though. On my other thread, a fellow said that the Type 24 tubes tend to have the problem more than others. Would that be the best place to start?


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Mon 25, 2020 5:50 am 
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Location: Near Brandon, Iowa
IMO every tube with a grid cap is a potential offender. If you don't have spare tubes, you could unsolder the caps then remove them carefully (they are glued to the tube envelope with water glass, a very brittle adhesive). Heat up the caps and knock out all of the old solder. Then dress the exposed wire coming out of the tube with fine sandpaper, reinstall the cap, and solder in place with new solder.


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 Post subject: Re: 1931 Philco 370 volume erratic
PostPosted: May Mon 25, 2020 7:02 am 
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Joined: Aug Wed 24, 2011 4:35 am
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Location: Sunnyvale CA
lorenz200w wrote:
IMO every tube with a grid cap is a potential offender. If you don't have spare tubes, you could unsolder the caps then remove them carefully (they are glued to the tube envelope with water glass, a very brittle adhesive). Heat up the caps and knock out all of the old solder. Then dress the exposed wire coming out of the tube with fine sandpaper, reinstall the cap, and solder in place with new solder.


I think you can just heat and suck out the solder, no need to remove the cap. I have had no issues doing that on maybe 10-15 tubes. The water-glass is pretty darn heat-resistant.

Brett


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