impedance switch kit?

[jake111]

I have an old prototype Stereomour that I'd like to install the output impedance switch kit on. But the transformers are different than the OT-2 at least label wise.
Will the switch kit work with these transformers?
Thanks, Jess

[Paul Birkeland]

The terminal numbers on the transformer will align with those in the impedance switch kit.

-PB

[jake111]

 What kind of improvement would there be if I upgrade to the OT-2?

[Paul Birkeland]

What kind of improvement would there be if I upgrade to the OT-2?

It's tough to say.  We would have to remember how many revisions there were to the iron the Stereomour before it went into production, then figure out which transformer you might have.  (None of the numbers on your transformer will indicate anything about that, the prototype winder never changes labels for revisions)

I would recommend just leaving it as-is.  It can be rather difficult to go in and troubleshoot an amplifier that was built as a prototype (instead of as a kit).

[Paul Joppa]

According to my notes, there were five prototype versions. I have in a box versions 2.0 and 3.0. No idea what happened to version 1.0 or 3.1; hopefully you have version 3.2 which was the first one with the right turns on both windings. You can measure the primary DC resistance, they should be 209 and 204 ohms. If that's the case then you have the first successful prototype of what became the OT-2 and there should be no significant difference between it and the production version.

If you get closer to 300 ohms (v1.0) or 250 ohms (v3.1) then your transformers deliver less power, but at lower distortion. There is a touch earlier treble rolloff, but the -3dB point is still well above 20kHz.

[jake111]

Yay! I got the 2.3. In faded pen on one of the transformers is v.3.2. Now I'm less apprehensive about doing anything to it. Thanks for checking your notes Paul.
Jess