The differential amplifier

[52 Bill]

Good question.
What exactly is the purpose of Q! & Q2?

That is the turn on delay mute. It delays turning on the voltage to the differential pair until cap C7 charges.

I only figured it out when I had one that had an open diode D7.

[jeeptechfred]

Cool, I can totally see that know that you guys spell it out. Is the negative feedback from Q6 being applied to the emitter of Q8 between r39a and r39 to modifiy its (Q8) effect on the output devices?

[teemuk]

Looks like a "bootstrap" to me: resistor R39 "isolates" the circuit from -Hv supply, and due to lack of any decoupling capacitance power amplifier's output signal, conveyed through C17 and R36 can modulate the node voltage rather freely. At peaks "pulling" voltage even below -Hv. This provides more "headroom" for negative voltage swings at stages of the input differential and in the voltage amplifier Q8.
If you look at it, voltage amp's collector load is similar "bootstrap" circuit too. Ignoring the mute circuit, R23 isolates from the +Hv supply, and power amp, acting as a buffer, conveys its output signal via C11, which effectively modulates voltage and can lift it above limit imposed by +Hv supply.

[jeeptechfred]

What is the definition of a bootstrap circuit? What does it accomplish? Sorry if the sounds like a over basic question but it's a term I hear from time to time but have no grasp of. Thanks.