Parallel universe?

[catch29]

I'm ready to do a re-furb' on my Heathkit MA-12's but am short of a 250uf+60uf 350vdc can, the old one doing a Mt Fuji impersonation. I can get a 300vdc but I'd be asking for trouble?. I have a 220uf (measuring 211) and a 47uf both 450v which I could parallel, plus a 68uf 400v. I've dug the goo out of the old can which I could cram the 258uf hybrid in and mount the 68uf separate under the chassis. Any thoughts?, I've heard that paralleling can upset resistances?. Be gentle with me , I'm learning this game (at 72 !).

[ppppenguin]

Electrolytics have very wide tolerances, often -25% to +50%. Using 220uF to replace 250uF is fine. The 47uF can be used to replace the 60uF or you can use your 68uF.

Unless you can measure the voltages, including during warm-up, I wouldn't use a 300V replacement.

[Mike Watterson]

I just repaired my S-VHS this week. 68uF 350V on the output of SMPSU input bridge rectifier was open circuit*. I used 2 x 400 uF @ 200V in series out of a 25 year old PC PSU (tested OK), with 100K Ohms across each, so in theory 200 uF at 400V. The bridge looks beefy, so the extra capacitance shouldn't be an issue. The valve rectifiers are more of a problem if you have excess capacitance.

I agree, a decent separate 220uF and 47uF is likely fine to replace a 250uF and 60uF.


(* Oddly it would power on if no AV cables plugged in. Also it drove the touch panel "buttons" on the TV mad if cables unplugged and VHS powered on. On bench with loop on scope you could see nice full wave modulated RF!)

[catch29]

Thank's, that would certainly make it easyer, I don't want to 'over engineer' it for no gain.