Replacement OT wiring for Carlsbro 50 Top

[cliffmustard]

NFB

Many thanks, I removed the NFB and the noise has gone I can actually play guitar though it now! Planning on replacing the electrolytics as there seems to be some other noises and odd harmonics going on (plus they are pretty old, possibly original).

I'll sort the PI coupling caps as well so I can try and get the NFB back to remove a bit of the hum.

Thanks again!

[cliffmustard]

Hope you don't mind me dragging this on. I'll be replacing the power filter caps. On the schematic it shows 4x50uf caps although in my amp there is 2x100uf and 2x68uf, can someone advise on what values I should choose?

Also, looking at the Spraugue Atoms as they seem reliable and not too bad price wise, any recommendations? Cheers

[cliffmustard]

Any comments? Cheers.

[oc disorder]

I would be inclined to replace as per the schematic.
You have 2 x 50uF in series giving a total of 25uF capacitance but double the voltage rating written
on the cap.I presume the voltage there is approx 450 volts.
So either you can fit 2 x 50uF 250v or 1 x 27 uF 500v per "string".
So 4 50's or 2 25uF 's.
The older valve amps always seem to have lower capacitance filtering compared to modern day.
Higher values seem to "tighten the sound".

Dont forget the 2 x 20uF filtering in the pre-amp. You may as well change them while you're there.

Sprague Atoms should be fine.

Also if you stick with the 2 x 50uF (two lots of) it's good practice to fit 4 equalizing resistors
220k is a nominal value.Put one across each capacitor ..they also act as bleeders for
when you turn the power off discharging the high voltage.

Couldn't help noticing you're in Bournemouth ..doing a circuit of the retirement homes?

Just had a quick squiz... looks like The Winchester is a popular spot !

[Steve Conner]

What size/shape of capacitors does it need?

If it's the big ones that clamp into holes in the chassis, F&T and Tube Amp Doctor have ones that will fit the original clamps. F&T have a 100+100uF, 500V part that would replace all four main filters, you can get it from Watford Valves.

IMO Sprague Atoms aren't worth the money, and they won't fit those clamps either, because they're axial. If you don't need a mechanical fit, just get whatever Taiwanese stuff is on sale at Rapid or Farnell.

These modern capacitors don't come in working voltages above 450, so you'll need to use them in series, and yes, use equalizing resistors as suggested.

[cliffmustard]

Cheers OC Disorder, that's brilliant, much appreciated. Unfortunately I got kicked off the retirement circuit as a cranked 50 Top doom experience wasn't quite what they were looking for....

The Winchester is not bad and plays all sorts of music, seen some good stuff there in the past, we seem to be struggling for good venues down here at the moment though ;(

Thanks Steve for the Heads up on Spragues, the caps I'm looking for are axial.

[pdf64]

Audiocap are a great UK source for F&T caps
High Voltage Axials Electrolytics (Over 300V) (F&T)
cheaper than Sprague

[Steve Conner]

I like the axial ones from Rapid, I've been using them by the dozen for a few years and haven't had any trouble yet.
Rapid Electronics - Electronic Components

Cheers for the link to Audiocap, Peter, I think I've found the perfect smoothing caps for my hi-fi amp project.