Isolation transformer upgrade for old guitar amps

Step 3The amp

The amp
I picked up this funky little Gregory Mark I amp from Craigslist for ~$25. Gregory put date stamps on their cabinets, and this one dates to March 25, 1955. So this little guy is over 50 years old!

Paul Marossy has a great website dedicated to Gregory amps (in fact, the photos of the Mark I example on his site are mine.)

It's a typical low-wattage practice amp of the time. No tone control, only volume. Probably 1-2 watts of output power. It's great "living room" or recording amp.

Among the mods I've already done was adding a 1/4" jack for the speaker output. I just unplug the small speaker, and run the amp into one of my 4 ohm cabinets. The amp is easily twice as loud through a 2 X 12 cab... (with loads of bass, too.)

But it's also a typical non-isolated amp, and that safety issue need to be addressed...
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Author:gmoon