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SAE 2600 Power Transformer Wiring

Ewan Penkey

Ewan Penkey

New Member
Hi,
I have a Clair Bros SAE 2600 power amp in, and I'm measuring +-150V across the (120V) filter capacitors. The schematic says I should have +-105V. I'm in the UK, so I guess someone has made a mistake wiring the primary of the power transformer. The wiring colors aren't on the schematic, so I'm hoping someone might have another / better source of info, or some prior experience.
Many thanks

Ewan
 
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All of my manuals in that series only show North American power xfmrs. No clue if there were 240VAC only or multi tap xfmrs for the other markets.

Craig
 
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Would need more info:

Is there a problem? I mean, is it working, or down for repair for blowing fuses or something else? Are you measuring it properly with your meter? Meter set at DC volts or AC volts? I would think that a 30 volt difference (if there really is one) would cause the capacitors to heat up.

Did you just get it from the USA or have you always owned it?
 
Hi Cademan,
The amp has come to me from a customer I've repaired some valve guitar amps for, because it's "developed a hum" and he's realised it's valuable, and want's to know if it needs any servicing work, specifically capacitors.
I'm measuring 150 DC volts across the 120V rated main filter capacitors.
The owner got from ebay in the UK about five years ago.
 
Is it 240 volt amp? In other words, if it were wired for 120 and plugged into 240, you would see sparks, smoke, blown transformer etc., and not just 30 volts over spec.

If it were wired for 240 and plugged into 240, then it really cannot produce any over voltage unless there was a short in a winding in the power transformer and in which case, it would get hot and possibly smoke within seconds or a minute.

If it has developed a hum, it just sounds like bad power supply capacitors but you might also want to check or replace the single bridge rectifier (if it has one) or check or replace any individual diodes. A bad but not shorted diode can also cause hum.
 
I wish I knew if it was a 240V amp, that would give me a clue.
It has two bridge rectifiers in parallel, to which the wiring looks original, so it's already deviating somewhat from the schematic.
I don't want to replace any capacitors until I have resolved the voltage issue. I have 150V across caps designed for 120V, so that's bad, and I would guess, could be the main culprit of the hum too.
The amp is also missing the guards over the output devices, so it's dangerous in it's present condition too. I've found a couple of poor repairs one one of the driver boards. It looks like this amp may have had an unfortunate history.
 
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Ok, it seems that whoever did the conversion to 240V only did half the job. There are two windings on the primary, which are joined in series for 240V operation. They got that bit right, but there are also two main windings off the secondary, The red pair were at 202V (off my bulb limiter) and the green pair, which supplied 148V (again off my limiter). So I swapped the wires to the green pair and am now getting 115V DC across my filter caps, which is still a little high, but in the right ball-park at least. Now I can go shopping for caps and whatever else this amp is going to need.
IMG_20221115_160613.jpg IMG_20221115_161311.jpg IMG_20221115_161457.jpg
Thanks for all your replies .


 
Ewan Penkey said:
I wish I knew if it was a 240V amp, that would give me a clue.
It has two bridge rectifiers in parallel, to which the wiring looks original, so it's already deviating somewhat from the schematic.
I don't want to replace any capacitors until I have resolved the voltage issue. I have 150V across caps designed for 120V, so that's bad, and I would guess, could be the main culprit of the hum too.
The amp is also missing the guards over the output devices, so it's dangerous in it's present condition too. I've found a couple of poor repairs one one of the driver boards. It looks like this amp may have had an unfortunate history.
Click to expand...
Sorry to late here but do you have 4 wires on the primary? Does it say “export” on the back? If you have 105 volts on the secondary it is normal.
 
Ewan Penkey said:
Ok, it seems that whoever did the conversion to 240V only did half the job. There are two windings on the primary, which are joined in series for 240V operation. They got that bit right, but there are also two main windings off the secondary, The red pair were at 202V (off my bulb limiter) and the green pair, which supplied 148V (again off my limiter). So I swapped the wires to the green pair and am now getting 115V DC across my filter caps, which is still a little high, but in the right ball-park at least. Now I can go shopping for caps and whatever else this amp is going to need.
View attachment 2714762 View attachment 2714763 View attachment 2714764
Thanks for all your replies .


Click to expand...
Yes it’s a 220 volts transformer.
 
Ewan Penkey said:
Hi,
I have a Clair Bros SAE 2600 power amp in, and I'm measuring +-150V across the (120V) filter capacitors. The schematic says I should have +-105V. I'm in the UK, so I guess someone has made a mistake wiring the primary of the power transformer. The wiring colors aren't on the schematic, so I'm hoping someone might have another / better source of info, or some prior experience.
Many thanks

Ewan
Click to expand...
Hi Ewan,

I have the wiring conversion if you like , mail me if you like
 
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