Bad Filter Cap?

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JoeTele
Posts: 127
Joined: Sun Oct 27, 2013 2:20 pm
Location: Milwaukee, WI

Bad Filter Cap?

Post by JoeTele »

I'm just checking the high voltage power power supply on a tube tester that's been my project for awhile. I've found that I'm losing about 12 volts off a 500 volt supply across a choke with no load on the supply. For testing purposes, I've isolated the stage such that the rectifying diodes feed straight into the choke, exit it, and then go to ground through a single 20uf 600v filter cap. I grounded the cap through an ammeter and as best I can eyeball the 10ma scale, am seeing at most 300 or so microamps of current, well under the 600+ua that the charts, by my estimation (15uf and 22uf values stated only), say is acceptable for an electrolytic of that voltage and value (http://www.tpub.com/celec/54.htm). The choke is about 134 ohms of DC resistance. When I short the choke out it goes from about 488 back up to 500v.

Are these conditions, particularly that voltage drop, acceptable, or may there be an issue with the cap? I don't have an ESR meter, but have assumed, perhaps incorrectly, that those are just a round about way to expose the same faults that a high voltage leakage test would but without using the high voltage.

I'd appreciate any help.

Thanks!

Joe
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xtian
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Re: Bad Filter Cap?

Post by xtian »

Putting a choke first, instead of a reservoir cap first, will result in lower peak voltage, according to Hammonds handy "Design Guide for Rectifier Use":

http://www.hammondmfg.com/pdf/5c007.pdf
I build and repair tube amps. http://amps.monkeymatic.com
JoeTele
Posts: 127
Joined: Sun Oct 27, 2013 2:20 pm
Location: Milwaukee, WI

Re: Bad Filter Cap?

Post by JoeTele »

And putting the first filter cap, on the front side of the choke, back in the circuit confirmed that! Back up to 500 volts at that stage.

Thanks xtian!

Joe
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