sunn beta lead, choked, low, farty output

[cooldude666]

my beta lead is sounding real lousy, the power amp is giving a really poor performance. the best way i can describe it is "farty". volume is lower than conversational when pushed to 10. The preamp section is working great, when I run preamp out -> beta power+ it sounds great. A little more velcro like than with the beta lead power amp but that's the sound of the power+. Anyone have any ideas what might be wrong? The caps "look" good (whatever that means) and when I prod them i dont get any weird sounds from the amp like I do when I have obviously bad electrolytics. Ive read posts about the power transistors going bad in these, is that likely my problem? How to I test them? Just replace them and pray?

[Enzo]

Tell me any brand and any model amp that has not had output transistors fail. OK, among amps that HAVE transistors.

When output transistors fail, you generally have blowing fuses.

Start at the start, verify the power supplies are up to voltage and clean. Make sure none are missing from the circuits. Frankly as transistors go, I;d probably be more concerned over drivers from your description. Open resistors too. Cracked traces or solder is a common problem in any amp.

Most bad parts don't look a darn bit different from good ones.

[cooldude666]

Tell me any brand and any model amp that has not had output transistors fail. OK, among amps that HAVE transistors.

When output transistors fail, you generally have blowing fuses.

Start at the start, verify the power supplies are up to voltage and clean. Make sure none are missing from the circuits. Frankly as transistors go, I;d probably be more concerned over drivers from your description. Open resistors too. Cracked traces or solder is a common problem in any amp.

Most bad parts don't look a darn bit different from good ones.

I wish I could! This is the first solid state amp I've ever tried to fix that wasn't something stupid and obvious like a broken solder joint, or clearly blown resistor. Good to know that the transistors are a likely culprit in a malfunctioning SS amp.

More concerned over drivers? The speakers? Pretty sure that's not what you mean, but if it is I can assure you they're not the culprit.

I'm really not into fixing these PCB amps. I can steal the board from my power+ since all the betas had the same power amp board, but I still want to fix this. I'll compare voltages to the manual and get checking continuity on the traces. The solder joints look good, they're still nice and shiny but maybe i'll reflow them for the hell of it.

[Enzo]

What I mean was, bad output transistors are not something this amp loses compared to others. Like saying Ford cars are known to get flat tires. Well so are all other kinds of cars.

The main heavy duty power transistors are your output transistors, The smaller transistors that drive them are called drivers. And in many amps there are even smaller yet transistors we call pre-drivers. No, I didn't mean the speakers.

Got a scope so we can see what the waveform looks like?