I'm helping a friend resurrect a 1960's Ampeg guitar amp by remote control. It has original aluminum electrolytic caps marked 25 uF and 12/15 V. If I ever knew what the dual voltage rating meant, that data is long gone from the memory banks. All help appreciated. Click on the image for more detail.

Thanks.

ak

 

HI AK,
This link explains.
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https://www.google.com/search?q=alu...cJMi02LjIuMi4xyAe-AYAIAA&sclient=gws-wiz-serp

 

I'm pretty sure 12 is the "working voltage" and 15 is the surge voltage.

But my formal electronics education is probably older than that amp.

 

Just because a cap is rated for 12 volts doesn't mean you can't substitute one of the same Farad rating but have a higher voltage. 35V comes to mind. If electrolytic caps are used - be sure you get the polarity right. If non-electrolytic caps are used replace them with non-electrolytic's. If push comes to shove you CAN use electrolytic's in series with the positive leads connected together and the negative leads independently connected. Numbers are hard for me but I think two caps in series like that adds the Farads together. I said "I think".

 

Numbers are hard for me but I think two caps in series like that adds the Farads together. I said "I think".

Incorrectamundo. Series caps combine the same as parallel resistors - the combined value always is less than the smallest of the group.

ak

 

This link explains.

Excellent. Explains, and rings a very faint bell.

ak

 

Spidey;
That is correct.
This surge/working voltage rating became popular when the very first solid state replacements in vacuum tube units were the rectifier diodes. When it was powered up, the tubes would take many seconds to warm up and start drawing current. During that period, the supply voltage “surged”. As the tubes became operational, the voltage was reduced to its working voltage.