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I use almost the same circuit in the majority of my tube supplies. However I don't use ZD1 because I'm not interested in clamping/regulating the voltage.I've found in practice, a bunch of RC filtering prior to the MOSFET isn't needed, and didn't result in much (if any) measurable improvement in ripple at the output. I always use 47uF/450V prior to the regulator, and the same 47uF/450V sitting on the gate (C1 in your picture), and get uV ripple on the output at modest currents (<100mA).Note that when the pot VR1 is set to half, you have 500k feeding into the 100K R1 that charges C1, which means that the MOSFET gate can see time constants over 10 seconds, meaning that it can take a full minute for the output to establish itself. For a tube circuit, this can be nice, as it gives time for the heaters to warm up and the tube to begin operating. But it can also mean that you twiddle the pot and the output doesn't change for a long time. If you have a high incoming voltage, and a large adjustment range, then heat-sinking the MOSFET becomes mandatory, doubly so if you think the circuit might be operating into short circuit conditions.
I use almost the same circuit in the majority of my tube supplies. However I don't use ZD1 because I'm not interested in clamping/regulating the voltage.
I've found in practice, a bunch of RC filtering prior to the MOSFET isn't needed, and didn't result in much (if any) measurable improvement in ripple at the output. I always use 47uF/450V prior to the regulator, and the same 47uF/450V sitting on the gate (C1 in your picture), and get uV ripple on the output at modest currents (<100mA).
Note that when the pot VR1 is set to half, you have 500k feeding into the 100K R1 that charges C1, which means that the MOSFET gate can see time constants over 10 seconds, meaning that it can take a full minute for the output to establish itself. For a tube circuit, this can be nice, as it gives time for the heaters to warm up and the tube to begin operating. But it can also mean that you twiddle the pot and the output doesn't change for a long time.
If you have a high incoming voltage, and a large adjustment range, then heat-sinking the MOSFET becomes mandatory, doubly so if you think the circuit might be operating into short circuit conditions.
