FWIW, 5 pages from the 1962 edition of the "Electronic Experimenter's
Handbook", starting at page 115, showed the design and construction of
"The Restorer ... gives your electrolytics a new lease on life", by
H. E. Sanders, W4CWK. It used a string of 8 NE-2's across a 720-volt
DC power supply (with dropping resistors, of course!-) to produce
selectable voltages in approximate 70-volt steps. Toward the end was
the sentence "Relatively new capacitors will form in a few minutes;
very old ones may take several hours."

A much-simpler circuit just for 450-volt caps was given in "Nuts & Volts
Magazine" in the last few years, but the page I tore and filed doesn't
have a date so I can't give a citation. But if you can cobble-up an
appropriate voltage source, it only used four additional components
(plus the capacitor to be formed); I'll try an ASCII schematic:

+------+--220K--+---NE2---+
| | | |
|+ | +--0.22C--+
450- | |
volt +---68K------------+
source 2 |
|- Cx (to be formed)
| |
+-------------------------+

Operation: "At initial power-on, the voltage across Cx is at zero and the
voltage across R2 is 450 volts, which lights NE2, the neon bulb. If Cx
is anywhere near healthy, it will slowly start to reform and charge up.
As the process continues (which can take hours), the voltage across R2
falls to the point where it is insufficient to keep the neon continuously
lit, at which time it begins to flash at a rate proportional to the amount
of current flowing through Cx. Once the neon lamp stops flashing, the
voltage across R2 is too low to light the lamp, and it can be assumed Cx
is fully charged and successfully reformed. For lower-voltage electro-
lytics, adjust the [source] voltage [to match the working voltage of Cx]."

--Myron, W0PBV.

--
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PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)