LCR smoothing cans - reform or replace?

[Steve Blackdog]

Hi Folks

I am working on a restoration (1980s ProAmp Viper 60). I was thinking of replacing all the electrolytics, as I am reckoning they have been untouched for at least 20 years - some look original. I don't have a leakage tester, so I am assuming the worst given their age and the likelihood that this has been stored somewhere damp and dusty for many years.

The amp has two big LCR 100uf 450v smoothing cans (1 3/8ths diameter by 2" high). No physical sign of damage. Aesthetics would say modern miniature snap in caps would look wrong - but as this isn't a holy grail amp, I am not sure it really matters. I can probably pick up some NOS LCRs for £20-30 for the pair - but they will have been sitting around for many years and are likely to need reforming anyway. Modern Vishays or Rubycons are likely to be under half the price of NOS and will be good to go.

What's the received wisdom on reforming old cans? Is it worth the bother? (I don't own a Variac)

Cheers

Steve

[Mick Bailey]

I frequently have to replace the LCR cans in Marshalls. They sometimes show signs of physical leakage (yellow/brown crud) and if not the ESR is starting to climb, indicating they're on their way out. I usually replace them with JJ but also have bought some decent ones from Modulus in the UK (own-branded).

My own view on reforming caps is that it's not a good long-term fix. I had a number of NOS caps recently that I set up with a variable voltage supply and measured the DC leakage. Initially this was high and after reforming over a few days the leakage measured fine. A couple of weeks went by and I was intending to use these caps in a build so just double-checked the leakage. Whilst not as bad as I originally measured, it was still too high. My own view is that an old capacitor could have suffered chemical changes which are not fully reversible by reforming.

[Leo_Gnardo]

For replacements approximately the same diameter, though a bit shorter, F&T offer excellent filter caps as well. They're out of Germany so should be easily available in Europe. In USA, Antique/Tubesandmore.com carries them, maybe other outfits also.

[Jon Snell]

I do not recommend NOS as they will be no better than the stock ones.
If faulty/leaky, fit new otherwise leave alone as they are probably OK.
An easy way to test for electrical leak is to charge them through a 100k resistor and monitor the voltage across the resistor when they have had 10minutes to equalize. The voltage drop should be less than10volts for a good capacitor.

[Steve Blackdog]

I frequently have to replace the LCR cans in Marshalls. They sometimes show signs of physical leakage (yellow/brown crud) and if not the ESR is starting to climb, indicating they're on their way out. I usually replace them with JJ but also have bought some decent ones from Modulus in the UK (own-branded).

There's no crud on the cans, but the date stamp is 86-15, so they are well past their design life. Decision made, I will replace with new.

I have looked at the MA brand cans - I hadn't realised they are Modulus own brand as I have seen them elsewhere too. As I am replacing 100uf 450v cans, is it appropriate to substitute with a 3 pole 50uf + 50uf 500v, wired in parallel (i.e. wiring the Red and Yellow together), or do I need to stick with a two pole 100uf? Also I am assuming it won't matter to go up to 500v is that right?

https://modulusamplification.com/Cap...p-P643443.aspx

Cheers

Steve

[Mick Bailey]

50uf+50uf is fine as a replacement for a 100uf. Check the dimensions though before buying. Increased voltage rating is better.