Ampeg BA-115 keeps burning rectifiers...help please

[scalefreak]

So, I picked up the bass combo that was blowing fuses and upon researching this amp, I replaced the output transistors without checking them. No difference. I check the rectifier and it was bad so I replaced it....but no sooner than I flipped the power switch, it cooked the new one. Now going back and checking, the old transistors were good. No apparent dead shorts anywhere or shirts to ground. What am I missing?

Thanks guys!

[DrGonz78]

What am I missing?

A light bulb limiter for testing of the amp and to stop it from frying out components that you replaced. Research the light bulb limiter and build one, it's real simple to make. It will prevent the amp under test from blowing fuses, rectifier diodes and transistors.

Also, we don't want to just start changing out parts on a whim and it may make the repair near impossible. So build the light bulb limiter and then start by testing voltages at test points in the power supply. What voltages are present on the amp? When you use the light bulb limiter it will allow you to start measuring voltages on the amp even if the amp is drawing too much current. The light bulb will limit that current and allow you to trouble shoot the amp. Do not connect any speakers at all until we know the amp is stable. Stable includes near Zero VDC on the speaker outputs, less than 200mv or so. If you follow this way of doing the trouble shooting you will have a better outcome towards repair.