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Testing older line-to-line audio transformers


New Member
Hi all,

I have a number of older line-to-line matching transformers (Peerless, Harman Kardon, and DuKane) that I found in a box full of old audio equipment, and I am wondering whether there is a way to test them with a multimeter to see if they are still functional.

I don't own any of the audio equipment that one would use these in or test them in, so that part is out of the question. But being transformers, I'm assuming there should be certain pins that I can test to check the continuity and the resistance to make sure that they're at least not dead.

Are these items known to routinely go bad under normal use, or do they usually last indefinitely provided they are not subject to abuse?

Is the multimeter approach in itself a good indicator of a particular transformer's viability, or might one test fine with the meter but still not function correctly?

Is there a particular pin readout that is common among these transformers, like "all input pins are 1 and 3, and all output pins are 4 and 6," for example, or are these different among manufacturers?

I've searched the web and can't find any of this information, so any help at all would be really appreciated.

Thanks for any replies!



Well-Known Member
Most Helpful Member
There is a very good chance the transformers are all good. Unless there is mechanical damage.


Well-Known Member
Most Helpful Member
Audio transformers were used in antique toooobs amplifiers. My first audio amplifier in 1961 was a Heathkit that used an input and an output transformer and a few vacuum tubes. None of my later audio amplifiers had audio transformers and had no vacuum tubes.


Well-Known Member
Most Helpful Member
i'm assuming that by "line" you mean "70V line transformers". these were used in audio distribution for the PA systems in department stores, factories, etc. by stepping up the voltage at the output of an amplifier you can run cables throughout a building with a large floor plan with fewer copper losses. wherever there was a speaker (usually in the ceiling) you would connect a transformer for the speaker ( line to 8 ohm usually). if you had a second floor, you connected the second floor through a line-to-line transformer. there were (and still are) not only tube amps with a 70V line output, but solid state amps as well (the first amplifier i bought for playing guitar through was a radio shack amplifier with 8 ohm, 16 ohm and 70V line outputs, and it was a 50 watt solid state amp). here's one in current production http://www.farnell.com/datasheets/2329549.pdf which has 25V, 70V, and 100V line outputs

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