Capacitor value mismatch ok?

[BobSimpson]

I'm rebuilding a bassman in AA864 format.
First 2 filter caps are spec'd at 70mfd 350V.
Closest I can find Atoms are 80mfd 450V.
F&T ditto.

Will not matching the schematic by that much be a problem?
Hard on tubes?

Thanks.

Bob Simpson

[martin manning]

No problem. You'll get 40uF for the series combination as opposed to 35.

[BobSimpson]

Thank you, Martin.
In the catalog, re: the pre-packaged sets of capacitors for Bassman, Atom 80mF 450V.
Got to be ok, I guess.

Bob

[pompeiisneaks]

Yeah the only fear on the first stage filtering is if the amp is tube rectified, and I think the amp you're referring to uses solid state. Too large of a cap on tube rectifiers will over stress them with inrush current. They usually specify in the datasheet to limit first stage capacitance to a specific value.

I'm pretty sure with yours, it's not tube rectified so nothing to worry about. Any increase in filtering just gives a stiffer nicer power supply.

~Phil

[Leo_Gnardo]

In cases like this I use 100 uF caps, never a problem, also they're easier to find. 350V rating as well. In SS rectified amps I go for the gusto, 220uF/350V. Plus there are brands much cheaper than overrated/overpriced/oversized Sprague Atoms, they also fit easily within the doghouse. F&T work perfectly fine.

[BobSimpson]

Thanks, guys!

I try to stay with the stock values, but sometimes they're hard to find.

[pdf64]

In regard of their capacitance value, vintage, high voltage ecaps of this grade were made to a wide tolerance band, eg +80 -30%, I’ve even seen +100 -50%. Hence from an engineering perspective, when compared to modern ecaps with a 20% tolerance spec, 70uF = 80 = 100uF, ie the capacitance value modern caps of a higher nominal value must fall within the tolerance band of vintage caps of a lower nominal value.
Getting bugged about nominal values here is looking down the wrong end of the telescope at things

[xtian]

IMO, F&T is a better value than Sprague/Atom.

[Stevem]

While your in there you can correct a factory build issue these and many Fender amps have that can lower the 120hz Idle noise floor on them.

The filter 2 more over ( filter for the 12AT7 tube) from the two you are replacing is grounded to the other previous filters and this filter being in the preamp should not get its ground from being daisy chained to ground.

You should run a new sperate ground wire for this filter and the last one in the amp.