Airpax / Stancor Military grade transformers

[valco]

Hi !

I recently got my hands on a bunch of these Airpax transformers from an old storage of surplus equipment from the army , but I haven´t been able to figure out what kind of transformer this is yet.  Is it a microphone transformer or something for some sort of radio equipment?

The transformers are labeled with Airpax AT- 601 821616 and a few that are similar and with similar numbering are named Stancor. They are also 8 pin

I´ve found these pages that i think is describing the transformer , but i can´t figure out what they are for and what the input ohm are and what the pin out are.

https://www.asap-distribution.com/nsn/nsn-parts/5950006923126/

https://www.asap-distribution.com/nsn/rfq/unisys-corp/5950006923126/821616/

https://www.parttarget.com/5950-00-692-3126_5950006923126_821616.html/-FD7C07EC-0909-4D98-A5F4-6F221325C10B

Does anyone have knowledge of these kind of transformers ?

Thanks

 

[valco]

Stancore

 

[valco]

Pin out

 

[Bo Deadly]

Measure DC resistance between each pins and find the ones that have continuity. That will tell you which are windings and which are just shields or the case or whatever. Once you identify the windings, put some AC in and see what you get out. Measuring impedance is a little harder but with DCR and a list of windings you can probably get some idea as to what they are.

 

[valco]

I sent signal thru on pin 1 and 2 and got them in return on 8 and 7 . Did the same on 3 +4 and got them out on 5 and 6 .
Then i sent a signal that measured 0,025 vac and got it out on the other side 0,065 vac , so if my calculations are right its a 1:3 transformer.

 

[valco]

Can they be used as microphone transformers ? or is the ratio too low ?

 

[ruffrecords]

Can they be used as microphone transformers ? or is the ratio too low ?

1:3 is fine for a semiconductor mic pre but too low for a tube one.

Cheers

Ian

 

[valco]

Do you mean a electret mic ? I´ve never heard of a semiconductor mic

 

[scott2000]

Do you mean a electret mic ? I´ve never heard of a semiconductor mic

Mic Pre

 

[Bo Deadly]

Those could just be different taps. You need to start with basic contitunity measurements using a digital multi-meter. Draw a picture with DC resistance between each pin and post it.

 

[valco]

Mic Pre

My bad. I totally misread it.

 

[valco]

Those could just be different taps. You need to start with basic contitunity measurements using a digital multi-meter. Draw a picture with DC resistance between each pin and post it.

I forgot about this , but now i finally got around doing it . Heres the picture . Does anyone make any sense of this ?

 

[rackmonkey]

This looks like an interstage transformer based on the pinout/DCR values you posted.

Assuming that 0,395k is the same as 395 ohms, it appears that you have split primary windings in the high 300s DCR. Using the rule of thumb of DCRx10 for a (very) rough estimate of nominal impedance,  that’s roughly 3500 Z per primary winding. The secondaries are high enough that they could be intended for “to grid” applications (50k or 60k transformers will have DCR readings anywhere from 1200 to up near 7000 ohms). But they could be lower impedance for some solid state applications as well (e.g., JFETs, emitter followers). The higher the DCR, the less the “10x” rule of thumb applies, so you have to use other methods to nail it down.

So basically, you can connect the split primary windings in parallel for somewhere in the neighborhood of 1500 Z - 1750 Z (too high for a mic preamp, not high enough for a line amp, unless you only want to connect older 600 ohm equipment to the input) or in series for somewhere around 7000 Z (which could be adequate for a line amp, although lower than ideal). The secondaries could be anywhere in the low -mid 10,000s nominal impedance in series (likely between 30k and 50k, in my experience) and  somewhere in the mid 1000s to low 10,000s in parallel.

So my educated guess is that it’s either an interstage transformer or it was designed for a non-audio application. A 1:3 winding ratio with these impedances backs that guess up. But as I said above, if you connect the primaries in series you could probably try it as a line to grid transformer, where it may or may not perform well.