Testing OT's

[tweed5259]

Hey I've got myself a used OT here and I want to test it to see if it's good, how do you perform tests on an OT with a Mutimeter? I've read somewhere how it's possible to check for shorted windings and other problems.

thanks.

[Amp Kat]

Try this
http://www.geofex.com/ampdbug/outtrans.htm

If it's out of the amp and you want to do a quick resistance check then you will need to determine the primary from the secondary. Most fender and others use blue, red and brown but not written in stone. Across two of them or the winding will be anywhere from 50 to 100 ohms and from the center tap wire to each side will be half. If you get that the chances are good that it is good. In the colors above the red is center tap and the blue and brown are acoss the winding.

[Enzo]

The secondary or speaker side will measure less than an ohm, so it is impossible to measure resistance meaningfully there. Just don't think "Oh no, it's shorted."

And you can check for shorts to the frame from each winding.

[tweed5259]

is it possible for the OT to work but just loose it's fidelity?

[MWJB]

If you use the word "work" in it's loosest possible sense maybe? If the amp had no fidelity and you were sure that the OT was to blame (and had already eliminated other causes like PI plate resistors, screen grid resistors, etc..), it could still allow the amp to make sound, usually sounds like a kazoo, no cleans if the primary is shorted - I wouldn't call this a "working" OT though.