Diode Strings


I am looking for opinions and suggestions. For my tube coil work I am in
need of some robust, high voltage diodes. Recently in some tube coil
experiments I have been sending back decent surges into my doubler diodes.
Needless to say they have not fared to well. So, I am going to order some 6
amp 1kV diodes from Digi-Key. These will be series strung using RC snubbers
across each diode. Each string will have 20 diodes, giving me about 20 kV
PIV -at- 6 amp continuos (each diode is rated for 400 amp surge for 8.3 uS).
My plan is to use the individual strings in a doubler circuit using max of
3250 VAC, and four strings arranged as a fullwave rectifier for use in a
6500 VAC circuit -at- 700 mA max.

My questions are: For the RC resistor value would a 1/4 or 1 watt be best?
What about value, 300K to 500K? For the caps I plan on using 0.001 uFd -at- 1
kV ceramic disk, sound ok?
Also, I have seen many people mention placing a resistor in series with the
diodes. A few ohms placed in series with each diode string sound good? I
don't want to have too large of a voltage drop.

I want to do this right the first time. This is much cheaper than getting
commercial diodes, about $60 versus about $300 from RF parts.

Anyone who has done this before, or has knowledge of potential problems,
please let me know.

As always, I am appreciative of any comments.


David Trimmell