Marmac XL120 Head Repair

[Sanitarium]

Well I've got this Marmac XL120 Amp head which is in need of some repair. I got it from an old shed I was looking through and after searching the net, some people seem to like how it sounds so I am gonna try and fix it up.
The amp was manufactured sometime in the 70's/80's in Glenamaddy in Ireland. The shop which used to make and sell them is still there, but they stopped making them a good while ago. The transformers are all hand wound.

When I first got it I replaced some of the fuses in it and turned it on. I got the glow from the valves and the power and standby LED's came on, but got a good bit of smoke coming from inside the amp. After testing the circuitry I think it might be that the transformers are blown. I have some pictures below which I hope you can have a look at and see if you see anything blatantly wrong with it.

Any info/advice/guidance on what to do would be very appreciated.

Thanks a lot.

(click for larger)

[Sanitarium]

More images:
(Click for larger)

[stokes]

Can you see where the smoke came from? How much smoke? What makes you think it is the trannies?An amp that has sat for years without being used (which it sounds to be the case) it is advisable to either replace the filters before firing it up,or at least bring it up to full voltage slowly with a variac.Nothing obvious in the photos,but my first suspect would be the filter caps.Could be screen grid resistors cooking,see if they look discolored or burnt.

[Sanitarium]

Thanks for replying,

When I first turned it on, I hit the power switch, and it was fine, then I tuned the standby switch up and the tubes glowed and then quite a bit of smoke came out. I don't know it was a single burst of smoke or if it was a continuous stream as I turned it off immediately.

I'm don't think it was sitting unused for years, as some of the solder jobs on it look fresh and the valves are all new. It looks like someone tried to revamp it and gave up.

There is no obvious burning inside the amp, and the smoke came too fast for it to be cause by something overheating, which is why I suspect it is the transformer.

I will take a look at the filter caps

Oh, and also notice one side of the transformer, the wrapping on it is perfectly smooth, and on the other side, it is all crumpled and discoloured.

Thanks again for the advice.

UPDATE: I tested the output transformer and I am sure that is the problem. The input transformer works fine and the output transformer has no impedance. I contacted the original manufacture (just a small shop on the west of Ireland) and he said he has a working transformer he could sell me. I am going to try and re-wind the transformer myself and see how that works.

Anyone re-wound a transformer before? This transformer was originally hand wound so I cant imagine it being tha tedious.

[Enzo]

What do you mean "no impedance?" You can;t measure impedance. if you measure resistance of the output winding - the speaker winding if you prefer - it will measure extremely low resistance because it is heavy wire and not many turns of it.

[Steve Conner]

If it only smoked when you flipped the standby switch, there's hope. I'd suspect the three big blue can capacitors above anything else: electrolytics are known to go bad with age.

But it could also be a short in the output transformer or choke, between primary and core.

Transformers can look like rusted wrecks and still work fine. If they have wax dribbling out of the windings or smell of burning, then it's time to worry. I'd be worrying about the little choke under the chassis there. If one of the capacitors shorted, it might well be that choke sending the smoke signals.