Stephen,
The current situation is that "A" reads -5.5 VDC and that this voltage doesn't go more negative when you increase Amplitude. Right?
The differential voltages "A+150V", "A-150V" and "A-20V" versus "A" are OK and also +/-10V are OK. Right?
Then "A-20V" is -25.5 V. With Amplitude at minimum the wiper of R246 connects to GND. Q234 draws a lot of base current via R233 and is in saturation. Now if you increase Amplitude a little? First "A-20V" will remain -25.5 V but now will pull the wiper negative, base current will decrease but Q234 remains in saturation (somewhat less deep), and "A" will hardly change. Now when you turn Amplitude more CW the wiper approaches about -5 V; the base current drops to almost zero and Q234 comes out of saturation. From then on Q234-base is (almost) at wiper voltage; the error between wiper voltage and "A" voltage drives Q234-current and Q233 base. "A" will go further negative when you rotate R246 further CW. Q234-emitter and base will go negative together but Q234-collector will hardly change (stay at about -5 V).
I would first of all try to see where it goes wrong when Amplitude is increased gradually.
Albert
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On Thu, Mar 17, 2022 at 11:01 AM, Stephen wrote:
On Wed, Mar 16, 2022 at 07:22 PM, Albert Otten wrote:
The design is nice enough to be discussed I think.
Albert
I agree, but I¡¯m really not good enough to analyze it properly.
