polytone mini brute 378A no sound

[pontiacpete]

I used the ones the schematic called for because I have several left over from a previous polytone repair.

So with the metal side down I guess that agrees. Using that sheet I attached the metal side is up your book is agreeing with "style 3", so that would they are in there correct now. I fires up. I have a signal on pin 1 but it's not a good signal. Looks more like a slightly rounded square wave. Nothing on pin 9

[Steve Conner]

The MJ802/4502 have remarkably high beta and current rating. More so than the MJ15003/4.

If you mixed up the pinout on your driver transistors, they could have got damaged, maybe even taken the LM391 with them.

[gbono]

Q1/2 are the NSDU07/57 - originally from National Semi. - their pin out (per the NSC data book 1982) is for a TO-202 package 55 which has 1= emitter 2 base 3=collector left to right with package oriented with bevel "up" - front view.

This doesn't match the MJE pin out.

[pontiacpete]

The MJE legs have to be bent to fit in the proper hole, that's where the confusion starts.

When I get back to it, I will try a new LM391

[pontiacpete]

Is it possible that the output transistors could have been damaged when using light bulb limiter?
Hate to have to put all 4 transistors when they are probably good still. THe traces at Q1 and 2 are not that rugged.

[tpoulsen]

MiniBrute 378 with schottky diode and biasadjustment

Q4 numbers look wrong, Collector and Emitter mixed up?

Hi. I know this is an old thread, but I have had this amp for repair. Replaced output- and drivertransistors, LM391, and a couple of resistors, and everything worked OK, at least for 1 hour. So now I have to start over again. Any good ideas? How do I adjust the bias?? Regards Torben

[Enzo]

Hi Torben, welcome

You should start all over, as in you really should start a new thread for your amp instead of adding to the end of a dead thread from 6 years ago.