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 Sudden change in volume level

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johnnycanuck



Join date : 2012-02-15

PostSubject: Sudden change in volume level   2012-02-15, 12:51 pm

I recently bought an unrestored Stromberg-Carlson Model 961. It is an AC/DC radio with six tubes. After turning it on, the volume is low and then, suddenly it becomes very loud. This also sometimes happens after the radio has been on for a while. Otherwise, the radio works well.

Which component could cause this?

Thanks.

Robert
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: Sudden change in volume level   2012-02-15, 3:20 pm

If it is unrestored, you MUST replace all the capacitors, especially in the power supply, because if one is breaking down (shorting) it will lower the B+ voltage..

There are many components that could cause your symptoms, but one suspect could be a volume control.
Also you may find the problem in one of the I.F. cans. There are some caps either inside or next to the bottom, They have problems with moisture and become contaminated with silver migration. Also tap the tubes and all components while running. Be careful of high voltages. Look for hairline cracks in resistors, wire leads and solder connections.

Capacior breakdown, and heat expansions on parts, are causes also. AVC may have issues.

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johnnycanuck



Join date : 2012-02-15

PostSubject: Thanks   2012-02-17, 9:39 am

Thanks for the advice Cliff.

Robert (Johnny Canuck)
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johnnycanuck



Join date : 2012-02-15

PostSubject: Update   2012-11-13, 11:40 am

Hello Cliff,

The radio developed a loud hum. I brought it to a fellow radio amateur who is a retired electrical engineer.

We noticed that two caps had been replaced by the previous owner. My friend suggested replacing the two electrolytics in a can in the power supply. We did so and he re-aligned the IF and the RF.

The radio works well. My point is that not all the caps in an old radio need to be replaced.

73,

Robert VE2AGE
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: Sudden change in volume level   2012-11-13, 12:24 pm

Well if your old caps that you didn't replace make the volume change then you need to replace them. You still need to replace all paper caps and electrolytics, Micas are OK and don't need to replace in most cases.
Use this analogy, you have an old tire, just because it is full of air, doesn't make it safe to drive with.
The same condition exists with all components. Tubes, resistors, caps, coils, even wire connections. Age has a deleterious effect.
You could have a tube or Cap breaking down, from excessive voltage. Your volume control may have a bad carbon trace that expands and contracts with heat. You could have cold solder joints. Many things to consider and give close inspection to.

Heat is usually a sign when conditions change fast. Even look at the tube sockets and make sure they all make firm contact. Look for Corrosion in the contacts and clean. Pull the tubes out and re-insert a few times to clean contacts.

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I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!
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johnnycanuck



Join date : 2012-02-15

PostSubject: Re: Sudden change in volume level   2012-11-13, 1:11 pm

Cliff,

Forgive an old man for not being clear! The volume no longer changes. I also replaced the line cord because the original was frayed in several places. I also replaced the plug with a polarized one so that the chassis is not hot.

I understand the effects of age -- they are a part of my daily reality!

Robert
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: Sudden change in volume level   2012-11-13, 10:14 pm

So tell us what the solution was, to the problem being solved? Then I will mark this as solved.

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johnnycanuck



Join date : 2012-02-15

PostSubject: Solution to loud hum in Stromberg-Carlson AC/DC AM   2012-11-14, 10:03 am

I added two electrolytics to replace the two in the existing can which was left in place. The IF and the RF coils were re-alinged by ear.

The radio works as well if not better than before the sudden change in volume and the loud hum.

Robert VE2AGE (johnnycanuck)
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