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Originally Posted by orbanp1
That colored diagram with the voltages is rather confusing, there are several different voltages marked at one node in different colors, never explaining it.
But if you have your own measurements that is fine.
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Peter
You're quite right
Originally, this diagram was only for my own use, to trace all the sections of the circuit that I checked. Color (green) was just to say that this line was checked for
continuity (no idea of voltage here) , then orange came to pinpoint a part of the circuit where I had to put attention...
Now I updated it to be more consistent toward voltage
See updated attached pdf file:
- 1 color = 1 potential
- Voltage measurement on each link, black = OK or no idea (no spec available), red = out of manufacturer specs
Impedance measurements are still here, and - in case of mismatch between real life and documentation- color coding of the resistors. (there were some variations depending on mfg serial number, and remember that I got this unit without any ID tag)
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That 5.85V at the half point is not that bad, you can leave it like that, it only means that the output will start clipping on one side a bit earlier, but there is still enough output there.
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I'm happy to learn that this value is acceptable
There is still a question pending. Should the reading be the same with or without load ?
Without load (loudspeaker disconnected) and unit ON, all the poles of the Ge transistors are on 13.5V potential, including common emitter with exception of AD156 collector, of course (0V). No voltage drop = no current....right ?
You told me about idle current. To be honnest I'm a bit confused here.
Should there be an idle current in any situation ?
Of course I should measure idle current as you suggested, but it requires to open the circuit, which is something I want to avoid for now, unless strictly necessary.
Quote:
You can "fine tune" the output voltage by adjusting W14, that 270 Ohm resistor, if you increase its value, the half voltage will increase.
You can change those thick film resistor values if you replace those boards with the printed resistors with individual resistors.
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Your idea makes sense, when measuring, W14 was only 243 instead of 270 Ohm (diagram)
I'm afraid replacing film resistor with individual resistor is beyond my capacities. The pitch of film resistor is quite fine: even if this PCB is old school one, such operation requires precision, ability and specialised tooling I don't have. And this is why some people are surgeons and some other are lumberjacks.
So let's consider any operation on the "W" resistor as the "last chance attempt", when everything else failed.
Best regards
Sebastien