Attempting to recap a couple of old Ampex 2010 suitcase amps

[famousmockingbird]

If anyone could give me some advice it would be great. I believe that there are 4 capacitors in one metal can in the power supply, what is the best way to approach this?

Here is a link to a schematic:

http://ftp.ampex.com/ampex/manuals/a.../2010schem.jpg

[korey]

2 ways that I can think of is to use 4 individual capacitors, or a single multi-tap can capacitor. The multi-tap is going to cost you more.

[mastodon]

I believe that there are 4 capacitors in one metal can in the power supply

Looks like it's three in a can. I have a few of those lying around, but if you haven't, then I'd suggest replacing them with separate caps. The only reason not to do that would be aesthetics, but I doubt that's an issue with this amp.

[Rod Coleman]

Be careful using modern caps for C5 (just after the rectifier). I would try to specify something with more than 500mA ripple carrying capacity for this position.

2x 82uF 400V Panasonic TSHA/HB/UP is a good choice, or Nichicon KX. Series connect the two caps, with 220K 1W across each, to force voltage sharing. Gives 41uF nominal, to match original 40uF; do not increase the value here, for preference, as rectifier is stressed if you do.

The others are less critical - use the same TSHA/HB/UP or Nichicon KX, 450V rated, values same or next higher in the range.

Panas & Nichicons will sound good, and give higher reliability than no-name caps or old ones. Get them from a real disti - ebay sellers may have ancient junk - old caps sound bad and are a waste of cash.

[famousmockingbird]

Thanks for all the advice. I definately have to do the caps in the power supply. Last night I fired her up with no tubes through a 60w bulb and there were no shorts in the tranny. Next I popped in the rectifier through a 100w bulb and after a few seconds the bulb began to glow really bright and bad sounds came through the speaker ( no smoke of fire ) and I quickly shut her down.
I will probably replace all the paper caps because they are all probably junk too, as for the mica caps I will probably leave them in there unless they are bad. Any thoughts on this will be appreciated.
Also I like Rod Coleman's idea of using two 82uf caps instead of the one 40uf. Will this be better than one cap because they are sharing their respective duty.

[century tek]

Originally Posted by mastodon

Looks like it's three in a can.

Nope! There's four. It also sounds like you have a short either in one of the cans capacitor taps, or the rectifier is shorted.

[famousmockingbird]

I checked the rectifier on my hickok 539b, no shorts, tested good. And yes there are four caps, 40uf, 20uf, 10uf, 4uf.
Any advice on coupling caps would also be great. I'm not trying to go overboard on these but it's a fun project and plus they would look and sound great on my deck while I BBQ.

[jjman]

Antique Electronic Supply is pretty good for multi-section cans but your values may be impossible to find. You may want to use a new can for the 3 higher values and a loose cap for the "4." You can go higher but not on the "40." So you could use a 20/20/20/20 by combining 20 & 20 for 40. Use another 20 for the 20. And use the last 20 for the 10.

I think you could use the 40/20/20/20 ( # C-EC40-20X3-525 ) for your 40/20/10/4 respectivley, and be fine, but others may have a reason not to do that. You need to verify size and mounting type before proceeding on a new can.

[famousmockingbird]

I am pretty sure that using capacitors in series and in parallel is the opposite of using resistors in series and parallel. Meaning that with capacitors in series the sum diminishes and in parallel they increase.
With that being said Rod Coleman is correct, if you wire two 82uf in series they will yield 41uf. Doesn't this increase the plate distance, and if so how will this effect the circuit?
Also I think jjman is correct also in saying wiring two 20uf in parallel will yield 40uf.

Which of these designs is the best way to go is what I am asking?

[Rod Coleman]

You can use 2x 82uF stacked [series] or 2x 20uF parallel, and they will both give the correct capacitance.

To choose between them, make sure the voltage rating is adequate in the 2x 20u case. Each 20uF should be 450/500V rated, and rated for 250mA or more for ripple current.

Stacking 2x 82uF[400V] in series will give more safety margin for voltage, and the Pana/Nichicon specified will carry the current.

If the specs can be met, you may choose based on which parts are easy to procure. Or easy to mount. Please use new parts though. I can't emphasise enough how bad old electrolytics do sound.