"Andy" wrote in message

I want to use an audio transformer to see if it helps to
reduce the ffect of an earth loop.

An old audio transformer I have come across is marked as
"LT44" and I that that LT44 is sometimes used to indicate
a 1:1 (or 600-ohm:600-ohm) transformer.

However when I measure the resistence of the tarnsformer
I get 650-ohms on the primary and 80-ohms on the
secondary which has a tap at 40-ohms.

That doesn't feel right.

A slip of paper with the transformer says LT.44
transistor driver transformer and says "impediance ratio
is 20K ohm to 1K ohm C.T.".

One thing is sure - this is a transformer with a turns ratio of something
like 4 to 1 to 8:1.

The secondary has a center tap. It might have been designed to be used as a
driver transformer in a transistor push-pull amplifier. I think these were
used in transistor radios in the 1960s.

The resistances have a ratio of about 8:1, but the specs of 20K to 1K
suggest a ratio of 4.5:1 since impedance ratio relates to the square of the
turns ratio.


(1) Why is my measurement of DC resistemce so very
different from the impendence on the specifications?

It looks like you got the specifications wrong. No way is this a 1:1
transformer.

(2) Is this LT44 useless as an audio transformer? I seem
to remember something about number of turns in the
windings being important for an audio coupling
transformer as well as the impedences.

Whether the transformer is good for audio depends on facts not in evidence,
such as power handling levels and frequency response. However, what you say
does not suggest good audio performance.

(3) Is it wrong to use "LT44" as an accepted shorthand
for a 600- ohm:600-ohm audio coupling transformer?

Yes, this is no way a 1:1 or 600:600 transformer.