Attached is a pic of the Leach Amp version I builtin the mid 1980's. To service, the boards can be taken outside the case and extended with a harness. The front mounted PCB implements a slow turn-on with logarithmic ramping of the volume and thump suppression. The circuit could be smarter and disconnect power if it fails to power up within a certain amount of time.
There is no power switch.

A nice cottage Industry home built amp ! What a lot of work though when you can get amps so cheaply ! Must of taken some time to build that ! Best Regards Paul

 

General experience:
1. Emitter resistors rarely die
2. If the output transistors pop, you have to get everything else RIGHT.
3. Low value resistors (100-250 ohms) in the output ckt ALWAYS need to be checked.
4. Bias regulator always set at minimum during unknown start-up. You can FORCE it to be zero by shorting the C-E junction of Q7
5. Initial tests are no speaker connected. Input signal connected. Variac. Scope on output. Monitor line current.
6. Bias best set with distortion analyzer. Never had the luxury.

DC out, no signal under 0.750 V. Usually mV. It's rare to find an amp with a DC adjust.

if you don't know the bias value, you need tosit at idle and no signal and watch the emitter voltage, line voltage currrent, the temperature and the voltage across the E-C of Q7. If your way off on bias, it will start heating up really fast.

I usually check for symetrical clipping and at full power.


It's POSSIBLE that with 4 emitter resistors in parallel, that there could be a bad one that cause the jump in the voltage across Re to be larger.

Thanks for that info ! When I get the fuses next week Ill see what damage I may have done to the amp ! I was only testing carefully for millivolts at the time it decided to blow ! Lesson Learnt ! Thanks Everyone ! I get back when I have more news ! Paul