As far as I can tell those two diodes are normally either non conducting or conducting so little they make no difference. The emitter volts of TR102 is only around 350 to 400mv. and that plus the vbe drop does not quite equal two diode drops. Its on a knife edge but I don't think work for setting current in any way in normal operation.
This is about Chrisr3521's problem, and I am hoping to be of help to him in order to solve this.
In no way am attacking him or useful contributions to the discussion by anyone else. I leave it up to him to judge what to do. Your comment about the late JLH in post 47 was provocative and implied your knowledge about audio amplifiers was greater than his, a man who spent a lifetime in the field of electronics. It would have been advisable before making comments to search the internet for information about the man's involvement in the field of electronics.
In no way am attacking him or useful contributions to the discussion by anyone else. I leave it up to him to judge what to do. Your comment about the late JLH in post 47 was provocative and implied your knowledge about audio amplifiers was greater than his, a man who spent a lifetime in the field of electronics. It would have been advisable before making comments to search the internet for information about the man's involvement in the field of electronics.
For what it may be worth, among the few online schematics I found there is one at UK vintage radio discussion forum "Quad circuit voltages" which are roughly handwritten on the copy of the schematic. These notes could be particularly where transistor lead voltages are noted. Associared resistor currents can be found from Ohms Law. With the handwritten notations on the schematic it would allow comparison and hopefully diagnosis/analysis of fault areas in Chrisrs amplifier. I have not visited the vintage radio discussion site but it might be useful to take a look there for clues.
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One step that one might recommend even if that does not solve the present issue is to replace all electrolytic capacitors since these can degrade in the long term and this equipment is cerrtainly likely to be decades old. It may be useful to draw up a table for the transistors showing emitter arrow direction and how moving base voltage levels more positive or less so changes the dynamics. I think the diodes in series with the resistor connecting to the supply rail is to bias the Vas transistor so it remains on after switch on which would allow use after the bootstrap capacitor is charged up. That same resistor serves as a collector load for the transistor ahead of the Vas.I am having a problem in getting to the knub of a 'wheel within a wheel'' as I have an issue with my pc where I cannot print screen so I can view the circuit on paper.
I had the use of a quad 33/303 pairing for a brief period in the early years of this centuary. It had been sent by freight from Auckland to Silverstream a suburb of the city of Upper Hutt by a friend in Auckland. We had moved from there after 26 years to Silverstream. I took the trouble to look inside the 303 and thought it had been built to a high grade of industrial construction. I did listen to the combo but not over an extended period. While this was a gift I felt obliged to pay for it at the same time we were spending money on new furnishings and appliances and so I thanked my friend and returned the equipment to him. Sadly he was a member of a weekend cycling group and had a cycle crash with fatal consequences. He was an audio diyer, his monika was Dark Lantern.
Sorry to hear of your friend's fate.
They were build nicely, very serviceable. Laced cabling. I can understand you would want to pay him for it.
They were build nicely, very serviceable. Laced cabling. I can understand you would want to pay him for it.
And success on the center voltage, R104 had gone high at 30k thanks all for help with this.