Phoenix Gold Phorum

Greetings! This is my first post here, but I've been repairing amps for a while. I have all the necessary equipment and am on www.diyaudio.com a bunch.



I have two of these amps on my bench currently, and both seem to have exactly the same problem - that would be failed output FETs.

Amp 1 is using IRF540 (NON N designation)
Amp 2 is using FB41N150

Both are using 10ohm gates at outputs
MPAS06 and MPSA56 drivers.

I've read in other posted threads that commonly these amps get upgraded to different outputs, IRF540N, FB41N150, FDP42AN15A0, or IPP200N15N3G. Some of these changes require a different GATE resistor.

Also Im having trouble identifying which OpAmp controls the bias, as I understand one which is out of spec could cause bias issues, excessive current, and sounds like that opAmp probably should be replaced.

I clipped off all the bad outputs, leaving some which seemed to still be testing OK, and got both amps to power on without any further issue, though I did not test anything at the output terminals just yet.


Can someone help me with correct component selection/combination for the output FETs, gates, and Bias OpAmp?

Thank you

Anyone?

I'm sorry for the delay, I thought I answered this when you first asked, but I must not have submitted the reply.

I've never seen a tantrum with anything but irf540's. I'm not sure where you found the other info but I've repaired dozens of tantrums, they all use Irf540 outputs.

First of all, there is not an op-amp controlling bias, it's done with discrete components. It uses two zener diodes and a 10k ntc thermistor for thermal tracking.

My next question is, where did you get the outputs and what are their full part numbers?