Stupid question, did you measure from the junction of R11 & source to the gate and R12 & source to the gate?
With the power off and the PSU discharged, check with a multimeter that P1 and P2 are functioning correctly, reset them to maximum resistance.
Power up, check that there is a voltage across P1 and P2, this shows that the JFETs are conducting current.
Apply a signal to the input, check with a scope (or a multimeter set for ac) that you have a signal at the junction of Q1/P1 and Q2/P2.
If you have no signal, the JFETS are probably short cct (24 volts across P1 or P2 would indicate this), power off and order some new (matched) ones, ensure that the PSU is fully discharged before replacing, it is important that you observe the static precautions to prevent damaging them.
If everything is good so far, power off and put in an order for new output devices, they are cheap enough if you are only using a single pair, they do not need matching.
Again, ensure that the PSU is fully discharged before replacing the output devices, and observe the static precautions.
Power up, check that there is a voltage across P1 and P2, this shows that the JFETs are conducting current.
Apply a signal to the input, check with a scope (or a multimeter set for ac) that you have a signal at the junction of Q1/P1 and Q2/P2.
If you have no signal, the JFETS are probably short cct (24 volts across P1 or P2 would indicate this), power off and order some new (matched) ones, ensure that the PSU is fully discharged before replacing, it is important that you observe the static precautions to prevent damaging them.
If everything is good so far, power off and put in an order for new output devices, they are cheap enough if you are only using a single pair, they do not need matching.
Again, ensure that the PSU is fully discharged before replacing the output devices, and observe the static precautions.
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Is this correct?
I thought the bias setting pots/variable resistors were set to zero resistance for the set up condition.
The test process I posted earlier is valid if you put a short across the gate and source of Q3 and Q4.
