Saturday, November 8, 2014

Ampeg Gemini 1 Full Wave Bridge

An Ampeg Gemini 1 showed up a little while ago with the owner complaining that it tripped the ground fault interrupter in his residence and had voltage on the faceplate. After removing the so called death cap-a likely suspect-and isolating and checking the power transformer for leakage, the only thing left that had a path to ground was the full wave, no center tap diode bridge.

Although the diodes checked ok with a voltmeter, 1N4007 replacement diodes are inexpensive, and the originals were probably 50 years old. Not willing to bet the ranch for 15 cents worth of diodes I replaced them. Looking at the original bridge, it had a quartet of old school diodes identified by yellow and red paint dots, not standard markings, some of which were worn off.

The above drawing with the lines properly oriented will build you a proper bridge. You can even take a chunk of large sized heat shrink tubing and use it as an insulator with a red marking for polarity.

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