Tubes and power supply

[R.G. Keen]

>If you are talking about National Semiconductor's LB-47 App Note,
>then the transistor mentioned there is NOT MOSFET, it's bipolar
>power NPN transistor - or actually there are two in darlington
>configuration. Check the BUxxx transistors, like BU206 (800V,3A),
>BU500 (700V 6A) or others.

Could be - I haven't looked at the actual appnote in a while. 
The circuit works, and with less consideration on drive 
requirements, with power MOSFETs. This lets you ignore the 
drive current and size the gate drive only on voltage considerations,
plus the normal nod to keeping the MOSFET from oscillating at 
VHF. 

I personally don't like passive drive arrangements to any power
bipolar device.