[sdiy] more fun with transformers: phase inverter from junk isolation transformer?

[anthony]

I have a transformer that I got out of an old answering machine. It looks 
like about 600-Ohm:600-Ohm center-tapped.
I didn't actually measure the DC resistance, but I looked at the overshoot 
when running a 2VPP square-wave through each winding on a scope. Doing this 
enough with a lot of known and unknown transformers and other inductors I've 
gotten to know about what higher impedence windings look like. Low impedence 
(like 8 Ohms) windings have nearly zero overshoot.

Anyway, I have a lot of puny little ones of these, but this one is big: 
about the size of inductors of the ilk used in tube amps.

I've always wanted to build a somewhat faithful clone of the Gibson 
GA-15RVT, but it uses a transformer as the phase inverter. I know that it's 
probably better to try to adapt a phase inverter like the one in say a Vox 
AC-15. But these two amps are quite different beasts, in spite of their 
similarities. I haven't actively priced a replacement phase inverter 
transformer, but all the ones that I have run across are very expensive for 
no more than they seem to be: an isolation transformer with one side having 
a center tap.

I guess if I can't use it this way I can use it as a mean octaver, although 
the cheapie 8-Ohm:1,000-Ohm center-tapped transformer that I got from Radio 
Shack seems better suited for the job: blasting the 8-Ohm end with an LM380 
amp and then fullwave rectifying the 1,000-Ohm CT side and... well you get 
the idea...


cheers,
Anthony