On Friday, September 27, 2019 at 1:48:15 PM UTC-4, Bo-Lennart wrote:
Hi all out there.
I found a transformer in my basement. I don't know if its a audio-output transformer or just a power transformer.
On top it's stamped "GALVIN MANUFACTURING CORPORATION",
and a model #: "25B31296-E" and a serial# ( ???? ) "138226"
At bottom there is 8 solder lugs, stamped: "1 to 8".
And at one side is 8 screw connector, labeled as "3A 12 11 2B 2A 10 1A 9"..
To me it looks more like a tube output transformator, more than a power transformer.
It seems to be from the 1940 or somewhere around there.
Anyone know what it is, and have some kind of "schematic" of the transformer.
Many thanks in advance
Bo-Lennart Karlsson
Falun, SWEDEN
Galvin Manufacturing is the company that produced Motorola products out of Chicago, Illinois, USA. It is easy enough to trace it out using a small AC power-supply and a good True RMS VOM.
https://www.radioremembered.org/xfmr.htm takes you to the RMA (Radio Manufacturers' Association) Transformer color-code for power transformers. Motorola, being a founding member of the RMA would typically follow these codes, but for their military stuff that followed a different code, sometimes.
Audio Output Transformers usually have Green-Black-Green (and mixes) on the secondary side, and Blue-Red-Blue (and mixes) on the primary side.
Note that transformers often have multiple taps on the same winding. So:
a) Using your Ohms setting isolate the various windings from each other. A single winding will show continuity, but with variations in resistance from one tap to the next.
b) Isolate the windings from the lowest total resistance to the most total resistance - this is trickier than it seems as you want to include all taps, but measure the complete winding, not an internal tap. Even more so, if, for instance, you have a 5V winding off a 120 V primary - it will have a lower resistance than the primary winding - more on this later. Bundle each winding and all the taps together so as not to mix them up.
c) Starting with the lowest-resistance winding, apply some reasonable, but low, AC voltage -say about 20 VAC or so.
d) Measure voltages on the other windings. By experimentation, you should be able to discern the purpose of the transformer, the primary winding and any taps, and the secondary windings as well.
As an example: A typical audio power for tube equipment here in the US would get 120 VAC on the primary side, have a B+ winding that might give something between 325 and 450 VAC, one or two 6.3 V filament windings and, perhaps a 5 V filament winding. That would be as many as five total windings. Some few even have dual primary windings to accommodate multiple input voltages. So, it is complicated.
An audio transformer may have multiple taps, but the turns ratio between the primary and the full secondary will be fixed, and there will be only two windings in total.
Take your time - it is almost entirely unlikely that you will be able to trace *that* transformer by its part number.
Hope that helps.
Peter Wieck
Melrose Park, PA