Capacitor working voltage...

[whoaru99]

So I've come to a small dilemma.

I have three EV 7100 amps and the tops of the PS main filter caps appear bulged. I think it is just the plastic that is bowed up but going to replace them anyway.

The dilemma is the rails are 60V at idle and the original capacitors are 63V rating. That is not much lattitude but my understanding is a cap should operate for its rated life so long as working voltage (amongst other parameter) is not exceeded and that some allow occasional surge voltage beyond rated.

Playing a bit more conservative, 80V caps seem like a logical choice but in the size constraints (35mm x 52mm snap-in) there are few choices.

If I stick with 63V rated, I can go up a bit in capacitance (from 10k uF to 12 or 15k) and still stay in the proper form factor and 105C rating of the current caps.

Thoughts?

 

[whoaru99]

Comments still welcome, but I pulled the trigger on some CDE 381LX series, 3000h @ 105C, 63WV, 79V surge rating.

Order deadline was approaching to have a chance at receiving them tomorrow...

 

[Hyperion]

I think you did the right thing - they should be fine, it's the old adage 'replace like-for-like what was there originally'.

 

[triode17]

So I've come to a small dilemma.

I have three EV 7100 amps and the tops of the PS main filter caps appear bulged. I think it is just the plastic that is bowed up but going to replace them anyway.

The dilemma is the rails are 60V at idle and the original capacitors are 63V rating. That is not much lattitude but my understanding is a cap should operate for its rated life so long as working voltage (amongst other parameter) is not exceeded and that some allow occasional surge voltage beyond rated.

Playing a bit more conservative, 80V caps seem like a logical choice but in the size constraints (35mm x 52mm snap-in) there are few choices.

If I stick with 63V rated, I can go up a bit in capacitance (from 10k uF to 12 or 15k) and still stay in the proper form factor and 105C rating of the current caps.

Thoughts?

There's a cap life rule per Morgan Jones in the Valve Amplifier book that says, if you can run a cap. at 89% of it's working voltage, it will double it's life. In your case 60v/63v=95%. No wonder the caps may have bulged over time. 63v/80v would =just 78%, which would be ideal, if you can fit them.

 

[whoaru99]

There's a cap life rule per Morgan Jones in the Valve Amplifier book that says, if you can run a cap. at 89% of it's working voltage, it will double it's life. In your case 60v/63v=95%. No wonder the caps may have bulged over time. 63v/80v would =just 78%, which would be ideal, if you can fit them.

The caps are not actually bulged nor exhibit any signs of leakage. It's just the plastic cover is distorted.

There is zero room for the next larger physical size. 35mm x 50/52mm is the max size that will fit.

The amps are more than 20 years old and still working. If the 63V Cornell Dublier replacement caps work for as long as the original 63V Samyoung caps (yes, that is the original capacitor brand - never seen that one before) I probably won't see the end of the useful life.

 

[gadget73]

If you're changing them and need to keep the physical size, I'd probably be more inclined to bump the voltage rather than the value.

Not personally a fan of things running right at the ragged edge of ratings. The stock 100v filter caps in my Phase Linear were running at 104 volts, and did so for 35 years before I changed them. The new ones are 160v rated anyway.

 

[whoaru99]

The problem with the 80V caps is the ones that fit of same capacitance were rated only 85C, whereas the originals were rated 105C. This is a compact 1RU amp with the capacitors right by the power transformer. In fact, the 1RU height and the proximity to the transformer is why larger caps won't fit.

Given the longevity of the originals, I took the chance that 63V working, 79V surge rating, is better than 85C for this application.

 

[gadget73]

yeah sometimes you have to take what you can get. I used an 80v cap in my Allied rebuild, same as stock voltage. The original was working perfectly fine when removed after 47 years.

 

[mbz]

Either way (63V,105C 80V 85C) I don't think you will have a problem. The 63V caps will last as long as the originals and then some.
However my preference would have been 80V, 85C. The 105C rating is tough to meet without trade offs. The 85C cap will have better
spec's in terms of tan delta/esr and ripple handling. Not familiar with the amp, I could be swayed to 105C if it's class A or some bigun
that momentarily blacks out the neighborhood when powered on.

 

[whoaru99]

One amp down (as in new main filter caps) two more to go.

As you see, there is no extra room in these amps to do much more with caps.

 

[whoaru99]

"Bulged" capacitor top and actually not bulged in the slightest capacitor. The bow in the top cover is a bit more than 1/8". To a casual observer it looked like the caps were ready to spew any minute. LOL.

 

[crispycircuit]

Nice Amp. I think you did good. Maybe install a couple CL-80s, one in each AC leg.....