2SB755 Transistor Data?

[Enzo]

Heat by touch works for me - just watch to see if it is getting hot. Nothing cosmic.

You could watch the commutating xstrs with the scope, but I think I would note where the LV rail is on teh scope and then when the output waveform tries to exceed that levl, either the HV rail kicks in like it should and the waveform looks OK, or it doesn't work and the waveform gets all funky bumping against its limits. Remember too there are separate pos and neg commutators.

[bob p]

Idled for a couple of hours under no load with no problems.
Now I'm trying idling into a load on each channel. If that goes well, I'll try small signals.

[bob p]

Well, its fixed.

I've checked the bias and it doesn't drift out of spec after a couple of hours at idle. With a 1 KHz test signal its putting out 45 V RMS into 8R. that's the amp's rated power of 250W RMS.

I was reluctant to torture test it with sine wave drive -- by the time I was able to dial the output power up to 45 volts to check the power output, my 300W power resistor was too hot to handle. Remembering what you said about Carver amps not liking sine wave torture tests because of the light weight heatsinks, I dialed it back down to 100W and re calibrated the power meters. I've been testing it with loud music signals tonight and it sounds great.

I haven't tried to torture test the protection circuit -- I'm not cavalier enough to short the outputs together while the amp is running. But I did try to drive the amp into a very difficult low Z speaker load at high output power, and the amp did go into protection (as I expected it would) and then came back online. So far so good...

So without testing each of the individual protection circuits, it looks like both the amp and the protection circuit are working.

Enzo, thanks so much for your help -- I truly appreciate all of the time that you've spent teaching me how to approach the repair of SS gear.

Now that this amp seems to be working, is there anything else that I need to worry about before I get too confident???

thanks again!

[Enzo]

The only thing we have to fear, is fear itself... or something like that.


Proof is in the pudding, if it works, it works. If it will play music into a load or a speaker for an extended period - an hour maybe - then I'd sign off on it and ship it. You cured your blow-up it seems.

Glad to help, I hope you gained some overall insights into the process.