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cyclecamper 15th January 2013 07:53 PM

Where to buy large bolt-terminal electrolytics w/ 600V rating
I'd really like to find some 400mfd to 1000mfd bolt-terminal aluminum electrolytic capacitors with a rating safe for use on a 500-volt B+. A 600v rating would have a comfortable margin. This is for a hot environment (big tube amp power supply, no fans). I see them used on eBay with even larger capacitance but used. I see a lot with a 450V rating that just won't do. I don't want oil bath or motor-start caps. Any help would be much appreciated.

KatieandDad 15th January 2013 08:13 PM

Seem easy enough to find....

PEH200ZH3470MU2 - EVOX RIFA - CAPACITOR, 470UF, 500V, 50X75 | Farnell United Kingdom

You can always use two 300V caps in series if you need 600V rating.

Enzo 15th January 2013 08:26 PM

Go to Mouser, and do a search for passive componenets/capacitors/aluminum electrolytic caps/aluminum electrolytic - screw terminal caps. That will get you in the ball park. You may hyave to settle for 550v, and that would be OK, since these ratings are working voltages. But there are also 630v ones. Here is a sample:
Aluminum Electrolytic Capacitors - Screw Terminal | Mouser.

And same story:
Aluminum Electrolytic Capacitors - Screw Terminal | Mouser

Now look at the prices. And note that I think one of them you can buy individually, but the others all have minimums of 4 or 8 pieces per order. Also note they don;t stock them, there is a four month lead time to order. You really want to spend over a grand on caps?

Ask yourself some questions. WHy do you need them to be screw-terminal caps? Why do they need to be such large values at such high voltages? Looking at a 300 watt AMpeg SVT, and the 660v B+ for the power tubes had a pair of 100uf/450v caps in series, as the main filter. Note they didn't try to get that voltage rating in a single cap. The 300w fender Bassman 300 has a pair of 330uf/450v in series across their 745v B+.

Consider using a number of smaller value caps in parallel. Caps with wire leads can be soldered to a circuit board in rows, as is commonly done.

cyclecamper 15th January 2013 08:44 PM

Yes, that's exactly what I found...I started at Mouser and Digikey. I hadn't expected them to be so expensive and sparsely stocked! I was hoping there was some secret I hadn't discovered.

What I really want is these:
Nichicon NX Series Electrolytic Caps
at the much cheaper Digikey price, but they don't stock any and want me to buy a large quantity.

I might ideed just use a lot of axial-lead or radial-lead caps.

cyclecamper 15th January 2013 09:47 PM

katieanddad, that cap has a great lifetime rating! But I'm reluctant to put a cap rated at only 500v on a 500v line.

I don't need such big caps just to filter adequately, but I want to see how it sounds for bass guitar and bigger caps model OK with that huge choke without needing any damping resistors; the big choke won't cause the voltage to overshoot at start-up or ring on transients. Some combinations might give me an unwanted tremolo LOL. If I put caps in series, I will add resistors to make sure the voltage divides somewhat evenly across the caps, and I was hoping to avoid such resistors. I was hoping to not reduce B+ much by adding the choke and subsequent cap(s). Then again the big cap calues probably leak a little an internal resistor.

Mouser seems EXPENSIVE and I don't want to wait 17 weeks.

I really hadn't expected them to be so expensive and difficult to obtain! That's what I get for being in software for 30 years and apparently way out of touch with prices and reality.

cyclecamper 15th January 2013 10:13 PM

OK I ended up buying one big bolt-top Nichicon 1000uf cap with a 650v rating, and 5 100uf axial-lead caps with 600v ratings. $150 total. All are new and fresh. I'll put one of the little caps across the big one as a bypass, and use that right after the bridge. Then I'll put the other 4 in parallel after then choke. If I'm going to use small axial-lead caps it seems to make more sense to use them in parallel than in series.

cyclecamper 15th January 2013 10:15 PM


cyclecamper 15th January 2013 11:21 PM

So they were all about $10 per 10uf, about the same rate for big caps as small. I was unprepared for that. I guess it's easier to mount one big than 10 small, but the 10 small might outperform the one big in some respects.

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