Hot 1203-80 PT

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marl3y
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Hot 1203-80 PT

Post by marl3y » Sun Sep 15, 2019 10:59 pm

Years ago I picked up the '68 "bare bones" kit, including the dual-voltage laydown transformer, 1203-80. It's always kinda hummed and got warm, but I didn't worry about it. I don't play the amp much, but recently busted it out. Anyway, I feel like something could be wrong, but not sure what. It get's hot, just on standby. For example. without any tubes installed and the amp on standby it draws about 0.5A (120V) and the temp of the end bell cover goes from 23C to 43C in 30 minutes. I had it on for an hour and it was pushing 60C. That's pretty hot, especially with no heaters nor HT current. Appreciate any thoughts and happy to make more tests. Thanks.

danman
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Re: Hot 1203-80 PT

Post by danman » Mon Sep 16, 2019 5:48 pm

That does sound a bit odd if there are no tubes installed. Try disconnecting both the high voltage secondary and filament leads from their respective points and then power up. At this point there should be nothing pulling any current from the PT. If it still gets warm, I would think there is a problem with the PT itself. If it stays cold then try connecting only the filament secondaries and powering up again without tubes. Check the PT again. If it stays cool like this there must be a wiring issue in the B+ supply, bad rectifier diodes or bad filter caps.

gloeidraad
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Re: Hot 1203-80 PT

Post by gloeidraad » Tue Sep 17, 2019 1:30 pm

I had something similar with a Marshall 6100 . The mounting bolts get very hot and the transformer also. What I did is to insulate the PT from the chassis. I put insulation washers between the PT and chassis and bolts and put shrink tubing on de bolts. Now everything stay cool. I think it has something to do with shorted magnetic field.

Erik

marl3y
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Re: Hot 1203-80 PT

Post by marl3y » Tue Sep 17, 2019 7:32 pm

Thanks for the suggestions. I decided to test the easiest thing first, since getting the secondaries unsoldered was going to be tricker, I isolated the PT iron from ground. I was suspicions as when I removed the end cover as I saw a dark mark. Sure enough in 15 minutes that spot went from 24C to 77C. So, looks like the PT is defective. I know it's been years, but any chance Heyboer is willing to do anything? Alternatively is there any approach to get in there and separate the wires that are probably arcing? Obviously I'd be careful and use a bulb limiter to verify.

[img]https://i.ibb.co/hDff4cP/IMG-1493.jpg[img]
Not sure why this isn't embedding correctly, but the link works.

Thanks again.

gloeidraad
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Re: Hot 1203-80 PT

Post by gloeidraad » Wed Sep 18, 2019 5:18 pm

Transformer is dead :( you can try to insulate de windings if they are on the outside but I don't think it will last.

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