replacement rectifier

[vaughandy]

Hey all,

I think I need to replace some rectifier diodes in an old amp I'm working on, as I keep blowing up a capacitor. I've double checked the circuit and orientation of all the caps and everything seems to be in order, which makes me think maybe the old rectifiers are shot and feeding AC current into the caps, hence the propensity for explosion.

Problem is, I have no idea about the specs on the rectifiers because the data sheet is in japanese. I'm going to enclose a schematic of the power supply wherein I want to replace the rectifiers. Any ideas what I need to buy?

[Tom Phillips]

I would say that common 1N4007 diodes would work.
Which cap keeps blowing up and what sound does the amp make (from the speaker) when or before the cap blows? How long does it take for the replacement cap to blow?

[Chuck H]

Are you being sure to recognise correct polarity? Which cap is blowing? Do you know your power tubes to be in good working condition? Also, depending on your mains voltage you may need to use 450V caps now instead of 400V.

As for diodes just use ordinary 1n4007 units. Be sure to replace the caps in the rectifier also. If they're leaking they could also cause some problems.

[vaughandy]

I would say that common 1N4007 diodes would work.
Which cap keeps blowing up and what sound does the amp make (from the speaker) when or before the cap blows? How long does it take for the replacement cap to blow?

the problem cap is the left side 250V 100 uF . It blows up after ~ 1 minute or so. I've messed with it a bit and have found that even a few seconds of being turned on make that particular cap crazy hot. interestingly the other 100 uF cap seems totally fine.

The speaker makes no noise, as the amp isn't working yet.

[vaughandy]

Are you being sure to recognise correct polarity? Which cap is blowing? Do you know your power tubes to be in good working condition? Also, depending on your mains voltage you may need to use 450V caps now instead of 400V.

As for diodes just use ordinary 1n4007 units. Be sure to replace the caps in the rectifier also. If they're leaking they could also cause some problems.

i've check and doubled checked the polarity and it's correct. That would definitely be the obvious answer, except that it isn't. :/

i definitely don't know that the power tubes are in working condition. could that impact this problem?

[J M Fahey]

It's a voltage doubler and those two caps are in series.
Your left cap can *must* be insulated from chassis or it will try to charge to, say, 300 to 400V, the full supply voltage, overheat, and eventually explode.
The right can is grounded, so no problem there.
You should measure full voltage on the left cap positive, and 1/2 of it on its can, which also is the right cap positive.
Good luck.