Can somebody take a look at this circuit for me?

Yet another likely problem is R3 having 1000 volts across it. I forget if 'ordinary resistors' (the common 1/4 watt thruhole) are rated at 200V, 500V, or what, but it could arc through, making the

1.01M look like an open circuit. I (and that opamp's input pin) would feel a lot more comfortable if it were several resistors in series. Five might be overkill, but 20 megohm is about the highest value commonly available, so that's what I would use.

Might have been R3 arcing internally with 1kV across it as I describe above.

What does the load look like? That (among the other things discussed) is important for stability and keeping the output from overshooting with an input change. Have you had a load on it when testing? You should, perhaps a resistor string of appropriate value.

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In which case you might consider editing them.

It's not normal to have a dollar symbol in there nor to have an Fet referenced as a *U* ( normally an IC ) !

Very much so. They combine with stray and device capacitance to cause phase shift. The higher the value - the worse the phase shift.

Graham

Are you *really* sure you should be let loose on designing circuits ?

Graham

Chuckle.

Maybe Kevin would like to do some of that bench stuff ?

Graham

Typically 250V IIRC. Another cute trap for the unwary.

Graham

The problem was reading the earlier poster's abbreviated English. It could have been clearer, "I added a zener between source and gate..." And I always though an s-g was a guitar model...

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