Heathkit UA-2 output tx wiring question - diyAudio
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Old 17th March 2008, 07:49 PM   #1
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Join Date: Feb 2008
Default Heathkit UA-2 output tx wiring question

As I'm sure many of you know, the color coding on old transformers is worthless. After years and years, they all look the bloody same.

So, I have a question for anyone familiar with the heathkit UA-2 amps. Or UA-1s for that matter (Just diff. bias circuit)

The primaries of the output tx's are about 175 ohms DC resistance to center tap and 75-80 Ohms DCR. from center tap to primary.

Or in other words, one is the plate, and the other is the screen.

But which.

If pin 9 is the plate, and 7 is the screen. which one should get which primary?

-------O 175 ohm dcr.

-----O 75-80 ohms dcr.

-----------------O center tap (B+)

-----O 75-80 ohms dcr

---------O 175 ohm dcr

Which ones go to which pins?


and btw, I've tried it both ways, and it sounds good, both ways. which means one of the ways, I'm cooking the hell out of the tubes

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Old 17th March 2008, 08:10 PM   #2
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Location: Taxland, New Jersey
The 175 ohm leads are the plate (pin 7) and the 75 ohm is the screen (pin 9). If the amp oscillates, reverse both the plate and screen connections to each tube.
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Old 19th March 2008, 01:20 AM   #3
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Thanks Hollow.

That is the way I wired them.

I've got another EL84 stereo power amp I built, and it's output tx's are about the same DCR, just not ultra-linear. So I wired the 175 to pin 7.

And boy, they sounded great.

My buddy thinks they are a poor mans MC-30.
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