Ignoramus6985 wrote:
On 2008-08-13, BobH wrote:
They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.

They are diodes. The Dialarc used a magamp for current control, no fancy
electronics.

After thinking about the circuit operation more, I don't think that
there is a large snap on or off of those diodes since they will only
switch around the AC line zero crossing. The voltage will only be a
couple of diode drops away from ground when they switch, so their abrupt
turn on is a pretty low amplitude event. It will still be fast but only
a couple of volts.

Bob