[Heathkit] sb-610 quad section cap

[eugene at hertzmail.com]

Hello all,

I've been slooowly working on an sb-610.  I am looking to replace the
4-section twist-lock capacitor can, part number 25-63. It is listed in
the parts section as having 30ufd, 20ufd, 20ufd, 20ufd.  There is no
mention of the working voltage.  These 4 sections are handling a maximum
voltage of +265V in the power supply section.  So I have a few
questions.

1. When looking for a replacement, are these twistlock style cans come
in different mounting sizes? I don't want to get one that won't
physically fit. Does anyone know what "size" I should look for?

2. Can anyone determine looking at the power supply circuit diagram if
there is any problem increasing the capacity of all 4 sections? Would
there be harm in doing 50ufd for all 4 sections? Might this raise the
corresponding voltages somewhat and might that not be good? Or, when
filtering rectified AC, the bigger cap the better? But then, why would
heathkit specify different capacities for each section? Why wouldn't
they just do 40/40/40/40? What about Working voltage? Is 500VDC enough? 

3. Does anyone know what an "acceptable" amount of ripple would be on
any of these sections? I am seeing some odd things that may a) mean my
caps are bad in the can or b)I am supposed to see what I am seeing and I
just don't know any better! 

For example. On the semi-circle section of the cap, when viewed on my
scope (in ac-coupling) I see a perfect descending ramp pattern where
Vp-p is about 4v.
Other sections have some crazy 2.5Hz .6vp-p waveform with a 60Hz .4vp-p
ripple super-imposed!

Should these sections be plain old dc with limited ripple? If not, then
it would seem like the values of these sections are important. If it
should be plain old dc, then it would seem that the capacity values are
less important (can be bigger), no?

----
Other questions. 
4. Should I replace all diodes? D1-D4 are silicon D5 and D6 are
selenium. Do I understand that selenium should be replaced as a matter
of good practice? These are handling some very high voltages, if I were
to replace them, what would I use? 

5. I know that it is good general practice to replace the electrolytics,
but what about the micas and ceramic discs? Assuming I have no specific
problems with any of them, do they fail? Or should I only change them if
they fail?

Mucho thanks in advance!

Eugene