Diode reliability?

[dmartn149]

I have this old Harman Kardon tube PA amp. It has a voltage doubler PS supplying about 650v to the power tube plates. It's working fine, but I noticed some brown discoloration on the aluminum body of one of the rectifier diodes and more discoloration on the chassis just under that diode. So my question is should I replace those diodes? Or wait and see? What might happen if one fails? Am I just worrying too much?

Thanks, Dan

[Tom Phillips]

It's probably not an issue. Can you show us pictures of the diodes and the surrounding area?

[J M Fahey]

Am I just worrying too much?

Thanks, Dan

Not really .... unless .....

[Mick Bailey]

Yes, post a picture. SS rectifiers usually fail short and blow the fuse, but they can go open. My reservation is that the diode may be getting hot due to an internal resistance that shouldn't be there.

[dmartn149]

Thanks for the input guys. Here is a picture. see the brown haze under the diode on the upper left.

[nosaj]

Thanks for the input guys. Here is a picture. see the brown haze under the diode on the upper left.
[ATTACH=CONFIG]44684[/ATTACH]

Looks like dirt.

nosaj

[dmartn149]

Well yeah... so how does dirt get in there? Do these kind of diodes ever spew? Honestly I have no clue what's inside that little metal case.

[nosaj]

Well yeah... so how does dirt get in there? Do these kind of diodes ever spew? Honestly I have no clue what's inside that little metal case.

To my knowledge there is no liquid in any diode. Dirt dust is in the air , it could've collected there .
If your really worried take a paint brush and move some of it. Put it under a magnifying glass. The PA is what 40+years old? I'd expect dust in there.

nosaj

[dmartn149]

It does work, and the diode tests good. I guess I should stop looking for trouble.
Thanks for looking and advising.

[Tom Phillips]

It does work, and the diode tests good. I guess I should stop looking for trouble...

Yes. Those are known as "Top Hat" diodes by the way. An old style popular in the late 1960's.

[Mick Bailey]

Those diodes are a fair way off the chassis. No liquid/gel contents in a diode. More likely for the adjacent resistor to get warm. In an old chassis there are convection currents (thermal air movement) that will gradually cause 'shadowing' of dust/dirt/wax in certain locations over the years.