67 plexi 100W (RIFA recap)

Matthews Guitars

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I would be curious to know how long reformed 50+ year old capacitors will last in service.
 

playloud

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I would reform them correctly with DC as they're out now, I wouldn't put them back in the amp just to reform them with an AC Variac.

Rookie question, but is this direct method more effective than the in-circuit variac method, or just faster/easier to measure progress? All caps are downstream of the rectifier(s), so ultimately receiving DC current, correct?
 

Seanxk

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Rookie question, but is this direct method more effective than the in-circuit variac method, or just faster/easier to measure progress? All caps are downstream of the rectifier(s), so ultimately receiving DC current, correct?
Well yes to effective and yes to measure progress, but it may take longer, but much less work than using the amp to provide the DC if the cap's aren't already in situ.
As you're doing the cap's one at a time and not all at once in the amp, you can monitor the current in each and use this as your guide for increasing voltage.
There's plenty on youtube about reforming units either with or without integrated power supplies, but this is my favorite video about '' cap's and people'' hehe,
 

neikeel

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I reform caps in x3 ways. In the amp with variac (less precise and not ideal).
On amps with simple PT wiring then the 100k resistor clipped in line from the rectifier is perfect (you can use this with 100w but you have to lift centre tap to caps and the bleeders). I like this because you monitor to voltage drop across the resistor and stop when you get below 3 or 4volts. Importantly if they don’t go below 5v you know they are leaky and should be replaced.
I have also made a jig with a PT and rectifier - basically a D.C. power supply and it has a series of 10k 2w decoupling resistors and croc clips and you can reform half a dozen caps at a time. I have it on the same board as my light bulb limiter.
 

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