Replacing filter caps with a different value

[EstynEstyn]

Hi all.

Can someone tell me what difference it would make replacing 4x 100uf Filter Caps with 4x 150uf Filter Caps?

Thanks.

[pdf64]

What is the context, eg what amp, how old are the existing caps?

[EstynEstyn]

I'm recapping a Selmer TnB 50 SV



It still has the original big old gold filter caps in it. I like using the F&T Caps for ease of replacement as then you don't have to change the clamps etc, but it seems like everywhere is out of stock of the 100uf till August or later. There still seems to be a good supply of 150uf, so I was considering replacing them with those.

Thanks.

[kleuck]

Slightly better filtering.

[pdf64]

Where are you based? Have you tried the German websites - tubetown, banzaimusic, askjanfirst http://www.die-wuestens.de/eindex.htm
The 150uF caps shouldn't cause a problem but it's an old amp so additional stress should be avoided if possible, eg to B+ winding.
Whatever, consider replacing the bridge rectifier diodes, balance resistors, and the critical components in the bias supply; the test for critical being 'is there a likely failure mode of this component that could cause loss of bias voltage?'.
Pete.

[EstynEstyn]

Thanks for the advice.

Pete, I tried Banzai and Tubetown, Audiocap and eBay. Everywhere seems to be out of F&T 100uf Hi-Voltage Caps. I was planning on replacing the Bias section anyhow. Also, should I up the balance resistors inline with the filters? ie. 150k instead of the current 100k?

Thanks again.

[Steve Conner]

It's the silicon rectified one, there's no rectifier tube to get overloaded. And the transformer in the SV has the same stack size as the older tube rectified TnBs, in spite of having a more efficient rectifier, so I think it's quite decently sized.

Also, electrolytics had a tolerance of -20, +80% until recently. So 150uF is actually within tolerance for a 100uF part. Just do it.

PS- The electrolytics (four blue "Eries" and two gold multi-section cans) were still good in mine.