Testing of Type 850S capacitors

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Testing of Type 850S capacitors

Postby WA2WVL » Tue Sep 26, 2006 6:23 pm

I had occasion to test some Centralab 50pf, npo, capacitors rated 5kv dc, under RF voltage. I was surprised how low their Q was.

With 900v rms (about 2 a) the caps were warm to the touch.
With 1300v rms (about 3a) they were HOT. I am sure they would explode under sustained operation. Testing was at 7.2MHz.

Based on these results the capacitor Q is about 300 (lower than any of the coils I would use in a high power amplifier) and I consider them to unsuitable for tuning in RF amplifiers.
Floyd
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Postby frank carcia » Wed Sep 27, 2006 8:52 am

Floyd,
How about in low pass filter application at lower voltages?
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Postby WA2WVL » Wed Sep 27, 2006 9:16 pm

Frank, a lowpass filter application is less critical and they should be OK for that. I am building a tube PA and wanted to use them to pretune band filters (3kv-4kv peak). I am starting construction of parallel plate capacitors with .125 spacing. The cap will have an adjustment range of about 10%.
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