Thank you for the reply and the information
I keep all this preciously, and at the end, all the parts of the puzzle will come along. WHAT failed and HOW it failed...
Well I choosed 8 Ohm spekers for a very good reason... they were already in the room!
Note that listening music on Monitor Audio 2 way bookshelves is not really a punishment, if you see what I mean
This evening, I decided to remove the upper and lower cover of a '71 Mannheim unit. Choose this one because is is the same year as the injured Essen, and it' s working perfectly with a clear & powerfull sound. Sometimes I realy feel it sounds better than my Denon micro-system, specially on voices ... but this is another debate. Basically a Mannheim is a Essen without 'Kurtz' wavelength, when the amplification section is quite similar (see diagrams)
The only minor differences:
- There's 1 supplementary Negative Feedback circuit on the Essen
- The 'Thick film' resistors are replaced with discrete units of similar value
(more space on the PCB , as the Mannheim is missing 'Kurtz' wavelength).
The rest of the stuff is quite similar, as far as the final stage is concerned.(GE transistors, polarisation & Bias stuff... copy & paste)
Now I performed the same test as I did with the Essen. I measured the voltage at the terminals of final stage transistors, with & without load. Surprise!... there was very few if no difference on the common emmiter with speaker connected or disconnected, (reading around V/2 in both cases) when on the Essen, both Emitter & Base set immediately to +VDC in the absence of load...
Any Idea about what is happening ??
I know this doesn't make a solution, but these are clues that we can add to the file. I will keep on studying the mannheim, it'll give precious informations to diagnose the Essen. The risk is to end up with 2 burned unit,...
Best regards
Sebastien