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Captn Dave 13th June 2009 11:32 PM

An Introduction and Laney Bass Amp Question
Hello everyone. I build and repair tube gear and post over at the tube board from time to time.

It seems friends are always bringing their solid state stuff to me to fix. No amount of protestation that I don't know jack about solid state stuff allays their suspicions that I'm just too lazy to help them out. Maybe I should just give up and learn something new.

An old pal brought over a Laney R3H Bass Amp that's crapped out. I checked over the power supply and that all looks good. It has a couple of SAP 15 transistors that appear to be set up in a push-pull arangement.

In my very limited experience with solid state equipment, it's usually either the power supply or the output transistors that fail but it's no fun to just replace something without first determining that it's bad. So, I'm ready to get after it with my signal gererator and scope and try to isolate the problem but I'd like to figure out the circuit first. (no schematic yet)

So here is my first question: If it is a push pull design, I imagine there is a phase splitter on the board somewhere. Can someone describe the way a solid state phase splitter works and the likely component. I don't see another transistor.

Second question: If I were to scope the input signal into the "possibly bad" output transistor, could I expect that it the signal would be shorted to ground within the transistor or open? ie would I need to remove the transistor first?

Third question: Colateral damage. Does an output transformer failure usually drag down a lot of other components with it?

That's enough noob questions for now.

I appreciate any help you guys can offer.


Tarzan 14th June 2009 01:51 PM

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