al goss wrote:
Need 800V reg'd .2A to .3A for Sg2 of Russian tetrode tube.
Anyone have ideas maybe tube regulator.
HV Zeners do not appear to stand up--failures.

The problem is the starting surge on the zeners. Set the zeners up
with a very high value resistor in series with them, so that you only
have a tiny trickle of current generated with the shunt regulator.

THEN, apply the regulated voltage from the shunt regulator to the base
of a big NPN pass transistor. You MAY need to use a darlington to get
enough gain to get it to regulate properly, but maybe not.

In theory, the transistor only needs to be rated for the voltage drop
across it, so you can use an MJE18006 transistor (1KV breakdown) without
any problem. In practice I like to have a little more safety margin.

The series regulator is a LOT more efficient than a shunt regulator.

If you do it with a tube in place of the transistor, consider the 6HV5,
maybe?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."