[Heathkit] SB-610 Selenium Diodes - caps across silicon diodes.

[Kenneth G. Gordon]

Concerning capacitors across silicon diodes: 

in my experience, this is a HIGHLY desireable thing to do, for the 
following reason: silicon diodes switch so quickly that often, depending 
on many factors including transformer impedance, load, and capacitor 
values, among others, the diodes can generate copious quantities of 
RF noise.

Installing capacitors across each diode and from each HV transformer 
lead to ground often eliminates this type of noise.

I have had much experience with this and remember that the first time I 
finally tracked down the source of the noise plaguing my receivers, I 
was utterly amazed. 

Since that time I routinely shunt each diode in ANY power supply I build 
which uses silicon diodes with a PROPERLY SIZED disk-ceramic cap. I 
don't always use the disk-ceramics from each HV transformer lead to 
ground, installing those only when necessary. 

Often, the center-tap of the transformer, or the connection to the power 
line through the primary, is close enough to ground to bypass RF noise 
from the bypassed diodes to ground through that connection.

Sometimes, it is not enough though, especially when the transformer in 
question does not have a centertap connection to ground.

Just my $0.02.

BTW, seleniums, for all their OTHER faults, are not as prone to this 
since they switch much more "softly".

Ken W7EKB