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I was looking at an 18 watt Lite layout using full wave SS rectification(simple diodes) and noticed a .1uf capacitor across the 2 HV leads where they attach to the diodes. One end of the cap hooks to one of the leads, while the other end of the cap hooks to the other lead. (HV winding has grounded center tap.) What is the purpose of this cap?
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It's probably there to suppress hash on the AC mains line. Caps parallel with the diodes are sometimes used for the same purpose and also reduce diode switching noise. Both AC hash and diode switching noise aren't always a problem but whoever designed the amp must have had a reason to put it in there."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz -
In keeping with my practice of kibitzing with designs, I'm going to.
The cap across the high voltage secondaries might be useful for suppressing diode turn-off noise, might be useful for suppressing hash from the AC line. That being said, you need a very manly diode to do that, not least because across the HV secondaries is a lot of high voltage.
If it were me, I'd either (1) snub the two diodes individually with an R in series with a C across each diode, or (2) use a FRED diode in both places and not need snubbing. I would probably use a MOV (and about here someone is going to say "use a TVS"instead; OK, fine) across the incoming primary line at the power transformer primary in preference to a simple cap.
But the purpose is, as noted, forever held only in the mind of the "designer".Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!
Oh, wait! That sounds familiar, somehow.Comment
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