"Favourite" is stretching things a bit - I don't like precision regulating at this voltage unless I really have to. The LR8 does a good job up to 10mA of output current, which is enough for the V+ in most double-triode circuits, but not enough for a power stage. One thing I have done is to float a medium-voltage regulator up to a high potential, but you have to be very careful to surround it with diodes so it does not get overvoltage under startup/shutdown or fault conditions.

Apart from valve (tube) HT supplies, the majority of designs I have done at this voltage have been in the input end of direct off-line switching power supplies. In these cases, you are dealing in phase-controlled high frequency FET switching, for which there are reference designs and a whole raft of available devices for the purpose.

Thanks for the info!

There are a lot of options in the switching power supply world, and with proper filtering they work quite well. However I am interested in linear regulation at this point.

That's odd - I thought you had said something about a double triode, but maybe I dreamed it.

I thinking of 12AX7 based pre-amp, but I will need a lower rail for that. Most older designs I see do not use a regulator on the plate supply, however a few newer design use switchers, but I never seen a linear regulator on the plate supply, although I am sure someone has done it.

I like the Texas TL783. Works OK for phantom power too.

Cheers

Ian

783 is good for more than 125v?

Preamp regulator: Look in the UTC transformer catalog; there are schematics of tube type regulated power supplies for tube gear. For low current "cheap and dirty" using gas filled regulator tubes, two 0D3 and a 0C3, all in series, will regulate 20 ma or so at 405 v....a series resistance from unregulated HT to the VR-tube string is required. The value of the series resistor depends on the unregulated DC supply voltage, and the sum of the maximum VR-tube current and the load.