[dude_500]

I've been looking at various electrostatic amplifiers. Upon looking into the blue hawaii amp and considering alternatives to the costly 2SA1968 source, I figured I would need to design an 800V current source if I want to make this amplifier on a budget, which is not terribly trivial since PNP BJT's don't typically go that high in voltage (with the exception of the 2SA1968). 
 
I read on a forum about the amplifier that it would be fine to use 600V rated pass transistors (which are still pretty hard to find, but not quite as costly as the 900V one). But I can't wrap my head around how this would be acceptable. For a highly negative output voltage (let's say -300V output), with a +-400V supply, that would put 700V across the current source. 
 
Maybe this is obvious as I'm by no means an expert in amplifier designs, but can someone shed some light on this?

 

[AmarokCZ]

In my design I had exactly same problem - N-MOSFETs was my solution (800V to 1KV MOSFET is quite available).
Theoretically speaking you could use N-FETs too in BH.

 

[kevin gilmore]

ixys parts are basically depletion mode n-channel mosfets. Some rated at 900V, some rated at over 1100v.
Cheap in the usa.  Otherwise look at the T2 schematic for how to use npn transistors combined with pnp's
to do a current source.