I recently picked up a couple of used transformers, AWA (Amalgamated
Wireless Association) model No 7XD1768.
AWA was a respected Australian manufacturer, these were sold to me as
microphone transformers.

There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms.

This seems WAY to low for a mic transformer, but what would a transformer
with these windings be used for?

Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not
a speaker transformer.

Any clues?
--
John Cafarella
End Of the Road Studio
Melbourne, Australia

There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms.

Thats @ DC what is the AC impedance.
It might be say 5K and ??
Steve
AllPro Electronics
www.Allproelectronics.com
Nashville, TN
Phone: 615.833.1810

In article ,
John Cafarella wrote:
I recently picked up a couple of used transformers, AWA (Amalgamated
Wireless Association) model No 7XD1768.
AWA was a respected Australian manufacturer, these were sold to me as
microphone transformers.

There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms.

This seems WAY to low for a mic transformer, but what would a transformer
with these windings be used for?

Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not
a speaker transformer.

Any clues?

Ribbon mikes? 8 ohms is kind of high for the primary on a ribbon but it
might be a cheaper model.

Maybe for some kind of moving coil dynamic with a very low number of turns
on the coil?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article ,
Stevaudio wrote:
Well that's the _real_ question, ain't it! At what frequency do you
measure at, is the next obvious question if you go down that path.

1k hz is good.
Measure the voltage total and the drop across a ~5k resistor and then the
current solve for R of the winding

The standard measurements are normally done at 1KC.

If you don't have a bench oscillator, though, a filament transformer
can be a surprisingly useful source, and you can make measurements at 50 Hz
which aren't going to be TOO far off if it's a wideband transformer. Be
sure not to clip it, though!
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Tue, 5 Aug 2003 17:27:00 +1000, "John Cafarella"
wrote:

Let me refine the question a bit: Are these DC resistances in the ballpark
of what you'd expect from a mic transformer?

Yes. For FET or vacuum tube loading. Can you measure turns
ratio?


Chris Hornbeck,
guyville{at}aristotle{dot}net

Measure the voltage across the primary. Measure the open circuit voltage
across the secondary. Ep/Es = your turns ratio
Ep / Es = square root of Zp / Zs
You can then find the primary Z for any value of load on the seconday. This
works for tightly coupled transformers. Stay away from frequency extremes
and high levels.
bg

John Cafarella wrote in message ...
I recently picked up a couple of used transformers, AWA (Amalgamated
Wireless Association) model No 7XD1768.
AWA was a respected Australian manufacturer, these were sold to me as
microphone transformers.

There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms.

This seems WAY to low for a mic transformer, but what would a transformer
with these windings be used for?

Physically it's round, about 1" diameter, and about 1-1/4" high, so it's
not
a speaker transformer.

Any clues?
--
John Cafarella
End Of the Road Studio
Melbourne, Australia

The DC resistance will typcially be a quarter or a tenth of the AC
impedance (measure it at 1kHz) but it's really not something you can
calculate like that. If they were sold to you as mic transformers, I'd
guess the two "8-ohm" windings would be 150-ohms in parallel or 600
ohms in series, but they could also be 150-ohms in series and 38 ohms
(for ribbon mics or MC phono cartridges) in parallel. Your best bet is
to hook the primaries up to an oscillator, terminate the secondary with
maybe a 10k or 50k resistor, and measure the gain. The amplification
factor equals the turns ratio, and the impedance ratio is the square of
that. So if you put in 100mV and get 1V out, then you've got 20dB
gain, a turns ratio of 1:10, and an impedance ratio of 1:100 (which
would mean 150:15k IF you actually are using a 150-ohm primary
arrangement). Next measure the overload point (level at which a 50Hz
tone visibly distorts on an oscilloscope) and the frequency response
(at an operating level safely below the overload point). If either of
these parameters look bad, try a different connection arrangement. You
can also measure the phase response at high and low frequencies, and
you can run a square wave through it and adjust the secondary loading
for optimum square-wave output.

ulysses


John Cafarella wrote:

I recently picked up a couple of used transformers, AWA (Amalgamated
Wireless Association) model No 7XD1768.
AWA was a respected Australian manufacturer, these were sold to me as
microphone transformers.

There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms.

This seems WAY to low for a mic transformer, but what would a transformer
with these windings be used for?

Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not
a speaker transformer.

Any clues?

John Cafarella wrote:

I recently picked up a couple of used transformers, AWA (Amalgamated
Wireless Association) model No 7XD1768.
AWA was a respected Australian manufacturer, these were sold to me as
microphone transformers.

There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms.

This seems WAY to low for a mic transformer, but what would a transformer
with these windings be used for?

Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not
a speaker transformer.

Any clues?

What are you planning to do with those transformers? If you decide that
you have no use for them i know someone that may need them eventually.



www.monsterisland.com

"Justin Ulysses Morse" wrote in message
...

Any clues?

Thanks to all for your assistance. Gotta say it again, what a great help
this group is! Plenty of homework for me now.

I bought them for use in a mic pre project I have in mind for the medium
term future. Until then, I might put two back to back, and see if they
sound nice as an pre-input to my mic pres.

The only transformer input pre that I have at this time is the OpAmp labs
unit, so it might be a nice flavour addition.

--
John Cafarella
End Of the Road Studio
Melbourne, Australia