I have an Ameritron AL-1200 amplifier, and it came (used) with a
capacitor problem. Upon inspection, 4 of the caps and 3 of the
resistors in the Plate supply have been replaced, and some of the caps
are in pretty sad shape (not to mention half of them are 220uf and the
other half 270uf...).

Upon a closer examination of the unit and schematics, I find the plate
voltage is expected to be at 3600 volts (more or less), the manual has a
warning about avoiding transformer taps that produce over 3700 volts,
and the total of the capacitor bank rating is 3600 volts. (8 caps in
series, 450volt rating. Each cap is 220 uf, so the entire pack is 3600
volts, 26.25 uf)

I was in high tech engineering (computers and peripherals) for 20 years,
and we never ran electrolytics at anywhere near their rated voltage.
Permissible margins for low voltage DC circuits were 50% or more
margin. Typical rule of thumb was 100% margin (a 10 volt cap running on
nominal 5 volt line, etc.). Even in an industry where every penny of
component cost was significant, submitting a design with electrolytics
running with as little 25% margin typically got a less than stellar
response during design reviews, to say the least.

So, I was very surprised to find the capacitor bank in the AL-1200
running at or slightly above the rating of the capacitors. It just
looks like a problem waiting to happen to me. Judging by the components
replaced by a previous owner, I think that at least some of the
capacitors failed in the past, possibly catastrophically... As I wish
to prevent (or at least reduce the likelihood of) this happening in the
future, I'm looking for capacitors that can replace the existing ones
with higher voltage units. Unfortunately, there just aren't many
manufacturers that have 500 volt electrolytics in their product line,
and probably few stocking distributors that would have any in stock (or
order them for a small order quantity).

The part numbers I have found that will work for me (in order of
preference) are listed he

Cornell Dubilier (CDE)
520C271T500AB2B 270uf 500 volts
500C311T500AB2B 31o uf 500 volts
520C341T500AJ2B
550C361T500AJ2B
500C381T500AJ2B
520C401T500AC2B
DCMC321T500AB2B
DCMC401T500AJ2B

ALS30/40 series BHC Aerovox
ALS334H331D3L500
ALS30A331DE500

All of these are "computer grade" with screw terminals, and range from
inverter duty down (in order, from the best are 550C, 520C, 500C,
DCMC).

Do you know of any distributor that currently stocks these? Price would
be good too...

I need 10 of any one part number. I am in process on gathering supplies
to make my own PCB to use 10 caps (instead of 8) so if I can get the 500
volt capacitors, the rated capacitor bank will be 5000 volts and 27 to
39 uf, which should provide a decent margin for a 3600 volt supply (and
not blow up if my line voltage rises and I see 3900 volts, which
happened to me at a former QTH). There's _just_ enough room for the
larger PCB for the 10 caps (and resistors) in place of the existing
board with 8 of each.

I know where to get CDE DCMC271T450AA2B (450 volt, 270uf) which would
give me a 4500 volt 27uf pack, but really would prefer to have the extra
margin of the 500 volt capacitors. I can wait a bit for reasonable lead
times, as the amplifier doesn't need to be in operation next week, but I
don't want to still be looking 3 or 4 months from now.

I'd appreciate any leads to suppliers of any of the above capacitors (or
their equivalents). I can't say that price is no object, or I'd just
buy a big QRO amp and sit back, but that's not the way I do things... I
should expect these caps are going to be somewhere north of $20 each,
even at Qty 10.

Thanks
--Rick AH7H