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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 13th Jun 2024, 5:21 pm   #1
John10b
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Default Capacitor identification

I’m restoring Bush TR82, after replacing all the Electrolytics, or so I thought, I realised that there was still one 8 uF unaccounted for.
The attached picture shows what I think is that capacitor, rather unfamiliar to me, any components please, thanks.
John
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Old 13th Jun 2024, 5:28 pm   #2
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Default Re: Capacitor identification

If you're meaning the slim white thing, yes it's an electrolytic - looks like it's the one in the discriminator that has its positive terminal connected to earth.

While you're in there, it makes sense to replace it. If it goes leaky it can cause perplexing audio distortion and odd AFC action.

Any 8uF electrolytic with a working-voltage above ten would be a good swap.
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Old 13th Jun 2024, 5:55 pm   #3
John10b
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Default Re: Capacitor identification

That’s the one, any reason why circuit designer would use this type all the other are plessey. This is an am set no fm. I should have said in #1 “ any comments please”. Thanks.
John
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Old 13th Jun 2024, 6:00 pm   #4
Station X
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Default Re: Capacitor identification

If the set's AM only it won't have a discriminator capacitor. What's the capacitor's circuit designation?
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Old 13th Jun 2024, 6:09 pm   #5
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Default Re: Capacitor identification

Quote:
Originally Posted by John10b View Post
That’s the one, any reason why circuit designer would use this type all the other are plessey. This is an am set no fm. I should have said in #1 “ any comments please”. Thanks.
John
Ah, apologies: I thought it was a FM set and this could have been the discriminator capacitor.
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Old 13th Jun 2024, 6:14 pm   #6
John10b
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Default Re: Capacitor identification

Thank you both, if you take a look at “BC327 biasing”, under this section you will see part of the Bush TR82 circuit to which this component is fitted, it is C24.

https://www.vintage-radio.net/forum/...20&postcount=4

John

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Old 13th Jun 2024, 6:42 pm   #7
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Default Re: Capacitor identification

Just replace it with a 10uF cap. It will be positive to earth.....it uses PNP transistors! It's just a decoupler...no idea why they would use this particular type unless it has something to do with construction to avoid possible instability. I just used an ordinary 10uF in mine (the original was O/C) and it's been fine.
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Old 13th Jun 2024, 6:57 pm   #8
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Default Re: Capacitor identification

Agreed, no reason to worry about this. The TR82 is a conservative design with nothing esoteric going on.
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Old 13th Jun 2024, 7:58 pm   #9
dazzlevision
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Default Re: Capacitor identification

There were four of these in my Decca TP85 L/M/VHF transistor radio. Judging from the markings, I'd say they were made by either Plessey or TCC.
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Old 13th Jun 2024, 10:35 pm   #10
John10b
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Default Re: Capacitor identification

Thank you all, I was trying to understand why the circuit designer would specify a single one of this type different to all the others.
John
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Old 14th Jun 2024, 6:56 pm   #11
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Default Re: Capacitor identification

It is possible the designer originally specified a component but the buying department found a special offer saving 2d. The set then has to be re-tested in the lab to make sure nothing goes wrong.
Really annoying when the component is a speaker which is used in several radio models and you have to fit samples to all the different cabinets to audition them...
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