SWR 750 blowing output transistors

[windsurf22]

I found the Q8 driver, which I had replaced , original was bad, has an Hfe of 307. I've ordered a few
new ones , and their gain is 64 . Would this high gain driver be causing my problem ? I've really found
nothing else bad. Q3 had been running a bit warm , board was a bit colored, as someone else had discovered also, and they increased the
feedback cap c5 to 250 pf. So I was going to change that to 200pf.

Enzo..thanks for the explanation of how the mute circuit works

[nevetslab]

An additional note to the mute circuit....upon turning off the amplifier, there's no longer any ACV applied to D7 to keep Q15 & Q16 turned on, and the V- HV rail effectively turns both off immediately, which stops the current flow into the input stage, which should yield a quiet muting of the output stage without any shutdown noises. I.E, delayed turn-on, instant turn-off, noise-free (if all is working ok).