[Heathkit] sb-610 quad section cap

[Jim Brannigan]

On the electrolytics:
Cans are not made anymore.  A few fellows make specialized items for a few 
radios.
The 610 can is too small to be "stuffed" with new components, so you will 
have to use discrete components.
40ufd @ 500VDC is fine.

Replace the diodes, they are prone to fail short.

It is good practice to replace all the resistors in the HV section of the 
scope.  They tend to drift higher in value.

With the above accomplished, you can see if the device needs more TLC.

Jim

> 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