Trace Elliot RAH600smx

[Francis Pettifer]

Hi all. Some of you may remember tracking me down a while ago. I was the guy in the waistcoat that was featured in Bassist Magazine. Now here's the problem. My amp was made in 1993, and after 22 years, one of the power amp channels has given up the ghost. It started humming at a gig, not a huge volume, and no signal from my bass was getting amplified. I used the amp in bi amp mode, driving a 1x18 and a 4x10+ a 4x5 bright box. The impedance that each power amp sees is 4ohms...the 1x18 was custom built for me by trace as a 500watt rms 4 ohm cab.

I know a bit about electronics, and have 'dabbled' with some successes and luckily only a few failures during the las 40 years.

The faulty Chanel seemed to be giving about -5volts ish DC. I have limited test gear...a multimeter, and figured that maybe the mosfets had died. The psu is giving +-75 volts, and the other power amp channel works perfectly.
I've replaced the mosfets, and the driver transistors, all readily available from RS online, but I can't get the amp to work...ice checked the diodes with my meter, and they all seem to be fine. If I substitute the j50 mosfets in various combinations with the originals the measured output voltage differs...ive had as much as -60volts now, but this can be reduced by swapping the mosfets again....what's going on? Please help. Regards Fran Pettifer

[Wiro]

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