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Transformer testing

Sam Cogley

Sam Cogley

Last of the Time Lords
Subscriber
How does one test an unknown transformer to find out what the specifications are? I have several transformers salvaged from a couple of Lowrey organs that I'd like to check out so they can possibly be used to build something interesting - they're all huge. Several times the size of the transformers on something more pedestrian like a Maggie PP amp.
 
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For power transformers or OPTs?


Personally I label all the wires, figure out what wires are on the same windings, and ohm them out.

Then, for power transformers, generally it's easy enough to know where the input is so I'll hook up a 12VAC wallwart to the input, taking note that it's probably at 14V, and then I measure the voltage across the windings. Do some math-a-magic and bingo-bango.

For example, I read two secondary windings, 41.2ohms and 560ohms; it's likely that the 560 is your HV. Turn on the 12VAC wart, note that it's putting out 14.1VAC, and I measure 63.5VAC out on the HV lines.

120 / 14.1 = x / 63.5

(where 120 is your wall voltage)

Rearrange for x; x = (120 / 14.1) * 63.5 = 540.4VAC

These will get you close enough, think, but keep in mind that these are unloaded ratings :thmbsp:


I hope that helps! I save money buying strange iron and use 'em by this method. Let me know if anything's unclear :)
 
Last edited:
thefragger said:
For power transformers or OPTs?
Click to expand...

Both.


Personally I label all the wires, figure out what wires are on the same windings, and ohm them out.

Then, for power transformers, generally it's easy enough to know where the input is so I'll hook up a 12VAC wallwart to the input, taking note that it's probably at 14V, and then I measure the voltage across the windings. Do some math-a-magic and bingo-bango.

For example, I read two secondary windings, 41.2ohms and 560ohms; it's likely that the 560 is your HV. Turn on the 12VAC wart, note that it's putting out 14.1VAC, and I measure 63.5VAC out on the HV lines.

120 / 14.1 = x / 63.5

(where 120 is your wall voltage)

Rearrange for x; x = (120 / 14.1) * 63.5 = 540.4VAC

These will get you close enough, think, but keep in mind that these are unloaded ratings :thmbsp:


I hope that helps! I save money buying strange iron and use 'em by this method. Let me know if anything's unclear :)
Click to expand...

I figured it was something easy like that. I'll check them out this week. Thanks!
 
Someone explained how to figure out strange OPTs to me somewhere, but I can't find the thread right now... maybe that person will chime in again in here :scratch2:
 
I'll get these figured out, then I can start trying to decide what sort of insane amplifier to build with them...
 
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