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maurycy 24th July 2007 02:52 AM

Question about CT transformer and Brian's Rev C power supply board

I am trying to follow the instructions posted by eddog in one of the threads about mounting CT to Brian's Rev C power supply board:
"Only four diodes should be mounted to the rev 3 power supply board, these are D8,D4,D5 and D1. Run a jumper from D6(outside hole) to D7(outside hole). Then run a jumperfrom D2(outside hole) to D3(outside hole). Also run a jumper from D2(inside hole) to D3(inside hole). Your centertapped transformer connects as such(on my working amp anyway), Your centertap wire goes to PG-(yes that is correct), your V- goes to AC2(inside) and your V+ goes to AC2(outside). You now have a working rev 3 amp."

I have the 42V CT transformer and power supply board with only 4 diodes. My transformer is this one: (6th on the list). It gives me 21-0-21. And here is where I am confused. Eddog mentioned V- and V+ but I do not know how do I determine which 21V is + and which one is - ?

Any help is appreciated.


AndrewT 24th July 2007 08:33 AM

the 21-0-21 is AC. They do not have a +ve or a -ve.
You have already identified the centre tap and where it goes.
Now connect one 21Vac to AC2 and the other 21Vac to the second AC2.
The rectifiers then direct the current to give you +ve and -ve outputs.

do check the PSU voltages BEFORE you connect the amplifiers.


do use a light bulb to power up the PSU the first time and EVERY time you add or modify something in the assembly.

galih 5th December 2009 04:20 PM

do use a light bulb to power up the PSU the first time and EVERY time you add or modify something in the assembly.[/QUOTE]

would you mind to give me the scheme of how to use a light bulb? and how many watts?

Atilla 5th December 2009 09:01 PM

You can find out how to build a simple light-bulb tester if you search the forums. It's basically just a light bulb connected in series and two switches.

It's a helpful thing to have.

Speedskater 5th December 2009 11:50 PM

1 Attachment(s)
The smaller the bulb the more protection (current limiting). However a real big power supply may not be happy with a small bulb.
(I used the symbols that I had available) US wiring.

AndrewT 7th December 2009 10:34 AM

Thanks to Speed for the new diagram.
The male plugs into the mains wall socket outlet.
The new equipment plugs into the female socket outlet.

The wiring applies to UK as well. Just the colours are different from the US.

You don't need the switches, the bulb tester works properly without any switches.

Any added switches simply make the tester more usable.

cjkpkg 7th December 2009 02:06 PM

check out This thread

galih 7th December 2009 05:18 PM

how do I know the circuit after the light-bulb tester works properly? whether the light bulb on or off?

Atilla 8th December 2009 07:24 AM

Check here for a very thorough description of the set-up and testing process : Building a Gainclone chip amp power supply.

Follow that and you won't go wrong.

AndrewT 8th December 2009 09:21 AM


Originally Posted by Atilla (
Follow that and you won't go wrong.

but the guy/gal does want to do his own research. He justs wants answers!

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