Davis Guitar Amp

[gomusicstl]

Hello everyone!

I'm new to this forum, but you all looked like a pretty knowledgeable bunch. I have a hand-wired Davis tube head, probably from the mid-60s. It has 3 6BQ5 power tubes, 3 6EU7 preamp tubes, and 3 different inputs, but it is not very loud. As far as I know, the caps and tubes are original (RCA).

Anyway, I'm no expert but I believe the amp needs a recap-- the amp seems not loud given the power tubes available, and distortion/breakup occurs without much cranking up of the volume control.

The problem is the two electrolytic caps, both Mallorys, don't seem to have a modern counterpart. The one inside the chassis (cardboard casing, axial) says:

+ Mallory +
Made in USA
40 MFD 450 VDC
20-45639
235-7114A

and the one sticking out of the top of the chassis (aluminum casing, 3 leads, axial) says:

Mallory
Type FP
Made in USA
MFD VDC
40 450
30 450
20 450
20-23964
235-7112Y 85C
87 812 C1 (stamped)

I called Mouser, and they say there is no exact exact replacement for these caps. What do you guys think? What caps would make good replacements, or am I stuck with what I have?

Thanks,
Joel @ GoMusicSTL

[dwhutchens]

These should work:

CE - USA 40µFx40µFx20µFx20µF / 525V

Sprague Atom 40µF / 500V

or if you have room in the chassis you could use some of the smaller and cheaper individual caps.

David

[Enzo]

And also look over at Antique Electronic Supply for selections of such caps.

[Robert M. Martinelli]

And.... keep in mind that electrolytic caps have large tolerances, ( up to 20% ) so it's not unusual for a 40 uF to read up to 45-48 uF.

In the "old times" filter caps could be found in multiples of 8 uf : 8,16,32,40, 64, nowadays the closest "standard" replacements for a 40uF are 33 and 47 uf.

Filter caps values are not all that critical, so I'd say 47 uF would be OK, going over that is not recommended with tube rectifiers because of the high current demand imposed by the large capacitance when switching on. If your amp's PS has silicon rectifiers you could even double the filter caps value without problems.

HTH

Best regards

Bob