Pilot SA260 transformers toast?

[kirk57]

I have a Pilot SA260 amp that i've stripped down to the chassis and was going to start to re-assemble.
Part of the teardown involved new wires to the power transformers since the one that were on it were very crumbled. I attached the wires as they had been, and now it seems something is amiss: When I connect the input wires to my variac and apply even a small amount of voltage, it blows the fuse on the variac (this has NEVER happened with this variac before)

The OPTs wires look better, but still not great, so I've left those alone. This amp was working (but not too well, rectifier tubes kept dying) when I shelved it. The teardown came a couple of years after that, if that matters

Can anybody suggest troubleshooting steps, or failing that can anybody recommend a service that can look at this thing? I think finding a replacement would be close to impossible...

 

[gadget73]

I'd pull open the end of the transformer where you replaced the wires and check that first. Could be that one is shorted or touching the case.

Are you testing this with nothing but the transformer primary wires connected, or is it fully hooked up? If its all hooked up, try unhooking everything but the primary to see if it blows the fuse. If that passes, try setting the variac to 12v and see if you get approximately 10% of what you would expect to get out of the various secondary windings.

 

[kirk57]

Transformer is not mounted in the amp, the only connection is the primary to the variac. I took the end bells off just in case it was shorting there. Unfortunately I get the same result: variac fuse blow as soon as I apply even a little voltage.

It appears I've broken it. Maybe time for a pro to have look...

 

[cademan]

At least the fuse on the variac was doing its job. Just as if the fuse were on the back of the amp itself.

I don't think the transformer is toast as you said it had worked before you tore into it.

If you know how to use your meter on the ohms settings, you will have to ohm out each primary and secondary. I bet your 120VAC input has one or both wires not on the right connections on the transformer.

 

[kirk57]

I've used my DMM and the DCR between the two 117 VAC lines is 0.8 ohms and OC between all other connection on the transformer. The other HV and heater lines DCR show expected values.

Not to say I haven't done something wrong, of course. But the wires look kind of 'toasted' so I'm not sure if it's me or if it's really broken.

 

[primosounds]

Did you check resistance between the wires and ground ? Seems to me that maybe the problem.
Also when you did the first AC check, you need to be sure that you had the correct AC lines. Sometimes those old cloth covered wires get faded and worse blackened so it is difficult to know what the original colors were. I have run across transformers where all the cloth covered wires look different shades of black! So if in doubt check the wires with meter for the proper DCR and mark them to be sure. good luck

 

[gadget73]

0.8 ohms sounds low for the primary. Schematic doesn't tell what it ought to be, but I happen to have mine open on the bench. I'll check it after dinner and let you know what mine rings out at.

 

[gadget73]

OK, my apologies. Fancy HP meter with 4 lead resistance check wired right across the primary gives 0.820 ohms. I was expecting a little over an ohm.