Ripple current Q for amp capacitors

Replacing vintage caps it’s often expensive to try to get a perfect match.  New caps are significantly smaller in physical size and have longer life spans. 

Ripple current for the main power supply caps is high, so you need caps with relatively large ripple handling capabilities.  The currents that come from the bridge rectifier are, by definition, high ripple.  A low ripple current cap here will overheat and die in an hour, even when V values are exceeded.  Trust me on that one.  

The DC current that comes OUT of the power supply (transformer, bridge, caps)  to the amp boards is not high ripple though, so small buffer caps (50-100uF or less) don’t need to worry so much.  

Also, all other things being equal, higher temp caps will last longer, even if neither is really temperature stressed, and also improves ripple current handling since  ripple currents cause heating.

Check the physical size, try to stay close in uF but feel free to go up in V and temperature ratings and make sure that you get caps designed to handle AC ripple. 

Of course, a physically smaller cap is also a good thing, so long as all conditions above are met.   If they are too much smaller you may need to apply some glue to ensure they aren’t rattling around on the board.  If your original caps are glued in and these are smaller, don’t rely on the tin leads alone for mounting. 

So it seemed to have a slight hum for a while. I moved out of a long term house, then rented for about 6 years and had the amp sitting in a box. When I built the theater, I bought the second PM1000. I have 11 channels in there (A Parasound Halo rounding it out). Everything is fed through a Tice Signature III power conditioner. I noticed the hum fairly soon I recall, but the build took a year so wasn't in the mood to hit something else and take things apart. But it got to the point I noticed it every time I went in the room.. and this is a treated space. But I think it might have seemed like more based on where I stood. If I put my ear against the wall where a speaker was, I could definitely hear it, and determined which amp it was.

As mentioned, i've rebuilt lots and lots of crt's and arcade pcb's as a hobby, and it is amazing what new caps will do to a crt. But I know those run far hotter. Still, I have always wondered if the same degredation happened in amps. The caps I took out, were as good of a reading as new ones were which completely surprised me. Did the hum go down? I would say it probably cut it in half.. but sadly the years of Orion amps and subs in my car in the 80's took a toll on my hearing so have a permanent slight ringing, so I can only judge by what range I can still hear. I can't stand in an open space and hear it easily like before.. I have to think about it and really try.. but if I go to a speaker I can definitely hear it. I used to have solid silver interconnects, but those started to get flaky at the connector, and I didn't want to have them in the system and not notice a channel  was out (like had happened before). I also thought the wires might be contributing to the hum, but I replaced 'everything' with Mogami wire to eliminate other sources before opening the amp.

The second PM1000 seems to be fine.. but it may have been taken out of a working environment right away and didn't have the 6-7 years of downtime my first one did. It's this downtime that has gotten me curious about reforming the caps. If I could get new date code ones I would just replace.

Thanks for all the help so far.. When I went this route I reached out to Noble Electronics who are the only authorized EAD service center to ask if there were any other possibilities or weak spots, and he only suggested the two large caps. I guess i'll focus on those, and maybe reach out and see if he'd suggest an alternative or what he uses.

I was reading about reforming the large caps. I'm still not entirely clear on a rig to try it, and i've been rebuilding crt monitors and late 70's-early 80's arcade machines as a hobby for 3 decades. But a question I had, and maybe you'd know, is how is applying a low voltage for a while to reform a cap, different than just leaving it plugged in for a long time, then unplugging it and letting it draw down? Shouldn't they naturally reformat themselves during regular use? 

If the caps are old enough, reforming them really isn't a thing unless you like the smell of a power transformer burning up. You might try this on a part only a few years old (5 on the outside). The easiest way is to put an incandescent lamp in series with the part when charging it. When the lamp goes out you're done. If it does not go out you're done also, except the cap goes in the waste bin.  

As far as which of the two caps to use: you’d have to do a little bit of research and see if both versions of the CDE caps were available at the time of the EAD1000 production. If so, then the designers made the choice. 

According to the specifications of EAD powermaster 1000, it is a 5-channel power amplifier with a power output of 200W RMS per channel into 8 ohms and 375W RMS per channel into 4 ohms. 

It looks like the 50V power supply filter capacitor might be a little too low for its duties, did you measure the rail voltage?

When I went this route I reached out to Noble Electronics who are the only authorized EAD service center to ask if there were any other possibilities or weak spots, and he only suggested the two large caps. I guess i’ll focus on those, and maybe reach out and see if he’d suggest an alternative or what he uses.

If budget and space allow, my recommendation would be the EPCOS / TDK B41456B8100M000, 100,000uF 63V capacitors, 12000 Hour life @ 85°C with 4mΩ ESR and 57A ripple current.

Lower ESR means lower internal operating temperature, and every 10°C difference will double or decrease the life of the capacitor! A capacitor rated for 12,000 hours at 85°C will have a useful life of 96,000 hours if operated at 55°C.

https://www.tdk-electronics.tdk.com/inf/20/30/db/aec/B41456_B41458.pdf