Figuring out max capacitance for a salvaged variable cap?

Thread Starter

BlackCow

Joined May 11, 2009
65
I don't have to be spot on, but what would be a good guesstimate of max capacitance for this variable capacitor? [see attached picture] I salvaged it out of a very old (non working) tube AM radio.

I noticed there are two leads, so I'm thinking it might be two variable caps in one?

I was thinking it might be around 400 pF max?
 

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debjit625

Joined Apr 17, 2010
790
Its Air Dielectric Gang Condenser (capacitor),these contains two or more sections the capacity of which can be changed from a single knob.The max capacity of each section is usually from 300 pf to 500 pf.

Good Luck
 

bertus

Joined Apr 5, 2008
22,270
Hello,

It is a double variable capacitor.
One has a large capacity (it has 9 plates in the stator).
The other is much smaller (it has only 5 stator plates, that are even cut out in the middle).



I added the picture with text for some explanation.

Bertus
 

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Last edited:

beenthere

Joined Apr 20, 2004
15,819
I noticed there are two leads, so I'm thinking it might be two variable caps in one?
Yes. One section tunes the antenna tank to select a station and the other tunes the local oscillator to beat with the station frequency and produce a 455 KHz difference for the IF stages.
 

Thread Starter

BlackCow

Joined May 11, 2009
65
Hello,

It is a double variable capacitor.
One has a large capacity (it has 9 plates in the stator).
The other is much smaller (it has only 5 stator plates, that are even cut out in the middle).

I added the picture with text for some explanation.

Bertus
Thanks, so is there an easy way to test to see what capacitance each bank has.

My multimeter is very basic and doesn't have a capacitor check. It seems like I really should invest in a better one!

Can anyone recommend a good meter that would do this and, if not asking too much, an inductance meter?
 

Paulo540

Joined Nov 23, 2009
191
Can anyone recommend a good meter that would do this and, if not asking too much, an inductance meter?
Well, I've had this here craftsman 82139 for at least 5 years and it's actually been very reliable and accurate, for a 20 dollar meter. Doesn't do inductance but I have a frequency generator for that.
 
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