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Vintage threads from the first ten years

Filter cap sub for BF Bassman?...

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1/30/2000 6:17 AM
Hackster	Filter cap sub for BF Bassman?... Hi, y'all... lil' help? Replacing the filters in a BF Bassman-- I can't find 70uf Atoms (or any others, for that matter). Isn't 70uf an awful lot of filtering anyway? Would a 40uf do? I realy hate to go up to 80uf. Grateful for any advice. John Edwards

1/30/2000 6:33 AM

Mr. Hackster-

Well, in BF Fender amps the Power Supply filter caps are installed in SERIES. This causes the 70湩 per cap rating to drop to 35湩. Installing 80湩 caps would rise the total filtering to 40湩. On the other hand, dropping all the way down to 40湩 would be practically unacceptable! That would only result in 20湩 in total filtering. Not reccomended.

Go with two fresh 80湩/450V Sprague TVA Atoms and your BF Bassman will be a very happy amp, with very little change in tone (if any).

IMHO

Good Luck!
Rob W.

1/30/2000 7:46 AM
Hackster	Thanks Rob... Somewhere I got the idea that putting caps in series increased the total rating, like with resistors-- thanks for straightening me out (note my handle!). Wonder how one 40uf in series with one 80uf would work in lieu of two 70's? Appreciate it, John

1/30/2000 5:51 PM

Hackster:

To figure out SERIES capacitance with 2 capicitors, use the following formula:

(C1 x C2)/(C1 + C2) = CTotal

So a 40湩 and an 80湩 would make the total 26.7湩.
That level would still be too low.

As far as the ratings that Fender used for filtering, they usually chose the smallest possible value that they could get away with. So tweaking the filtering up a LITTLE more really is only helping your situation. IMHO

Have Fun!
Rob W. :-)

:-)

1/31/2000 1:42 AM
Hackster	Gonna go with two 80's-- already have 'em in hand. Thanks again, Rob. John

2/1/2000 7:15 AM
Nils	Rob, FWIW, I think that the 5F6-A has two 60uF in parallel to ground, do you think that's overkill Nils

2/1/2000 5:10 PM
Rob W.	Nils- Well looking at the Fender schematic for the 5F6-A Bassman, I see two 20湩/600V caps in PARALLEL for the power supply filter. How to figure out PARALLEL capicitence: C1 + C2 = CTotal So, 20湩+20湩 = 40湩 The exact same rating as (2) 80湩 caps in SERIES. FYI Cheers! Rob W.

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