• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Audio Transformers

I have these three Stancor transformers in boxes marked:

Audio Transformer A-3321
From 1 or 2 6A6, 53's or 79's
To 3000 Ohms to carry .125 A.D.C.

Audio Transformer A-4406 P. P. Driver
From 2-45's or 2A3's
To 2-210's or 801's

Audio Transformer A-4405
P.P. Driver
From 1-2A5 or 42
Top 2-2A5's or 42's Class "B"

Are these power transformers or output transformers?

The instruction sheet says Primary connections, Plate-brown, C.T.- Red, Plate-Blue. Secondary Connections, 3000 ohms- Green and Black

Thanks for any help.
They're interstage transformers, "driver" indicating that they feed a power stage, usually a class B or AB2 stage that requires some driving power. The first one appears to be a low-power modulation transformer - a push-pull audio stage would modulate the DC that powers an RF amplifier stage. They are different from audio output transformers in that the secondary carries DC current.
Do you know of any schematics that would show interstage transformers in a circuit. Seems like they are power transformers? What would be the benefit or reason to use them?


It's not a complete schematic but it has the principle to look for. The purpose of your interstage transformer can be two fold: to split the audio signal into two opposed phases, or to deliver a beefed up audio signal at the final tubes.


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