Sorry - my bad! Typo in my previous message. R9 is 1k, as it should be. I checked again both across the resistor and from input to gate of jfet. Apologies.
I'm going to lift one leg of the thermistors to try and get a reading for these.
Which raises another question: for troubleshooting purposes, is there any reason I shouldn't take the thermistors and ztx's out? Would this remove the thermal compensation and current limiting completely, and maybe make it easier to find the fault?
Just did this. I get 575R for R3 and (about) 485R for R4. Remembering that the bias isn't as high is it will probably be eventually, these sound about right.
The ohmeter took a long time (on the order of a minute) to stabilise on these values. Why is that? Measuring other resistors takes a second or two, so it isn;t a low battery in the DMM. Something about the semiconductors in the circuit?
60mV = 6mA through the Jfet, which is perfect actually, no need to worry there. The 600 ohm R3 is part of the conceptual schematic, the real one with real parts uses different values. I = V/R so your 6mV result should read 6mA, which is on the money (0.006 x 10 = 60mV, which is more or less your readings across the 10 ohm resistor).
I would suggest looking carefully at R9/R10, If you got them reversed your input signal will be basically attenuated to zero and you will have no sound at all.
I would suggest looking carefully at R9/R10, If you got them reversed your input signal will be basically attenuated to zero and you will have no sound at all.
I'm happy to report that both are working. Turned out to be even more stupid than I foresaw.... I came to suspect a problem with the output connections, and it turned out that the speaker cables I was using to test it both had bad connectors at the amp end. (Slaps forehead... 
)
Sangram: many thanks for your help and input - even if the fault turned out to be elsewhere I learned some stuff looking for it...
Now on to next steps. First, getting the bias set correctly, since it is a little low for testing purposes at present.
Then I need to get a speaker protection circuit in there. I've previously used the circuit from Rod Elliott's ESP site, but had considered using the diyaudio circuit and boards. These are only available as a set with the soft start boards, however, and I'm not planning on doing those. They also seem to be stereo boards, so I'll have to spend $50 just on boards, which seems a little steep. Anyone have any ideas?
Finally, I need an on-off light... I have this idea to use several blue leds inside the case, maybe near the back with a reflector of some kind, so that the whole case will appear to glow from inside - visible through the mesh-like front of the apple cases. With a bit of luck it'll look like there is some kind of nuclear reaction powering the amps... hehehe...
)Sangram: many thanks for your help and input - even if the fault turned out to be elsewhere I learned some stuff looking for it...
Now on to next steps. First, getting the bias set correctly, since it is a little low for testing purposes at present.
Then I need to get a speaker protection circuit in there. I've previously used the circuit from Rod Elliott's ESP site, but had considered using the diyaudio circuit and boards. These are only available as a set with the soft start boards, however, and I'm not planning on doing those. They also seem to be stereo boards, so I'll have to spend $50 just on boards, which seems a little steep. Anyone have any ideas?
Finally, I need an on-off light... I have this idea to use several blue leds inside the case, maybe near the back with a reflector of some kind, so that the whole case will appear to glow from inside - visible through the mesh-like front of the apple cases. With a bit of luck it'll look like there is some kind of nuclear reaction powering the amps... hehehe...
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