Sunn Concert Bass Troubleshoot

[J M Fahey]

Ok Drew, I'm happy about your news. You did it !!!!! :tu:
Now use it as it is: not as a "Bedroom Warrior" (the crossover distortion will drive you crazy) but as the loud mother it is.
You'll get almost 200W RMS into 8 ohms with it. (150 plus for sure).
Bye.

[phatt]

As Phil does, I find your Drain voltages perfect. The Gate should be at "0" volts and the source slightly negative relative to it. The slight deviation compared to theory may be due to the fact that Sources are "force-fed" through a resistor from the -15V supply.

Thanks JMF,
Sadly sims don't give the novice those little gems of knowledge that you have collected.  
So thanks the sim now makes more sense,, good to know.

But for a chap like me starting out a hobby in electronics at the middle part of life,,, Sims do help put some of the puzzle together.

Yes Drew,, intermitant problems are the worst kind.
At least you got it fixed.
Phil.

[DrewV]

 It took awhile to find all the damage in this amp. When I got it the power board was floating inside the chassis, held up by the wiring that wasn't disconnected, the circuit breaker had been jumpered across. Every single electrolytic was or went OL before it was over, some (locations) even twice! All four emitter resistors were "going with the flow"! Power resistors were burnt and for a few seconds as I observed them smoking! Three of the power transistors were the wrong type. The two that were the right type were burned out.All three rectifiers were toast and various outher parts were missing or loose...and the jacks and pots were dirty, dirty, dirty! But... the transformers were good and most of the resistors and remaining capacitors. The jacks solid, switches clean. And the most beat up tiny little part, CR306, the only zener  in the house looking like it spent a little time in the garbage disposal, well, that worked. This amp is loud and clean and a tribute to the TONEQUEST of the early 1970's. Did I mention that this amp is LOUD?  Thanks Drew
P.S.The overdriven tone I was getting was coming from the speaker not the amp! I hooked up a Mesa Boogie Black Shadow and got nothing but loud & clean.