Litzendraht wrote:
In my day it was not only common to use equalizing resistors across
each diode, but a .01 disc ceramic as well.

In the olden days, silicon diodes were very expensive, and had process
variations that made individual diodes in a production run quite
different from each other. The original 1N400X series was a grading
process. The manufacturer attempted to make nothing but 1N4007's, but
that didn't always work out. The really bad diodes became 1N4001's,
and the really good diodes became 1N4007's.

[Just for grins, I just took a modern manufacture 1N4001, a diode rated
for 50 PIV use, and hooked it up to my 577/177 curve tracer, and I saw no
significant reverse leakage current all the way out to 1600V.]

The equalization resistors were used with the thought that they would
swamp the leakage current of the diodes in the reverse biased condition,
and make sure that each diode saw only its equal share of voltage.
The truth of the matter is the reverse leakage current will start to
rise rapidly when the diode starts entering its avalanche region, and
the next leakiest diode in the string will start to take over when the
leakiest one starts thinking about avalanching. The string balances,
and protects, itself.

-Chuck