Date: Sat, 30 Oct 2010 10:46:26 -1000
From: Ken Brown <ken.d.brown@hawaiiantel.net>
Subject: Re: [Amps] HV rectifier strings - to bypass or not?
> I'm getting ready to lay out the HV rectifier board for my YC156
> project, and it occurs to me to wonder if anyone has ever really heard
> HV rectifier "white noise" in the receiver? It would be simpler to
> forget about the per-diode bypass caps and just bypass the output as it
> leaves the board. The supply will be housed in a separate cabinet from
> the RF deck, but connected of course with bypassed leads for HV, (SHV
> connectors) 110VAC and control signals.
I thought the reason for capacitors and resistors paralleled with the
series diodes was to help equalize the voltage division across the
diodes, and reduce the chances of an unequal voltage division, exceeding
the voltage rating of one of the diodes. I did not think it was for
noise reduction. I had also heard that it was more important with
earlier manufactured diodes, due to lower voltage ratings and not quite
as good matching from one diode to another. With more modern production
diodes the voltage division tended to be more equal, reducing the need
for the resistors and capacitors.
DE N6KB
## The paralleled resistors were supposed to be there to equalize the
V drops. The purpose of the parallel caps was to eliminate switching
transients
when switch's from conduction to non conduction. Interesting enough, Ten-tec
still uses the resistor's in parallel with the diodes [no caps].....and
Ameritron
still uses caps [ and no resistors].
## KM1H came up with a better method... and that's to install one HV disc
ceramic
across each leg.....so 4 x caps in all. The purpose of these 4 x caps is to
bypass any
junk/transients coming in off the street. Of course the V rating has to be high
if a single
cap is used. You can get disc ceramic caps in 4700 pf @ 10/15 kv variety. [
Ceramite brand,
sold by mouser+ henry radio still has em]. IF .01 uf caps [10,000 pf]
installed across each diode,
and 8 x diodes used, you only have 10,000/8 = 1250 pf effectively across
each leg. If individual
caps used, .02uf @ 1 kv would be better. IMO... 4 x big caps, one per leg,
is more effective, and
messier than 32 x caps.
## On these YC-156/YU-148/3x3 amps, etc....with the HV supply in a separate
box..... use 2-3 x 4700 pf @
10/15 kv bypass disc ceramic caps for bypassing the B+ to chassis. I would
also install 1-3 x 500 pf @
10-20 kv TX doorknobs for bypass as well. [HEC/ITT-Jennings type]. The
doorknobs make for better bypassing
on the higher bands. The above is all inside the outboard B+ supply
box..[right at your SHV connector].
## I then install the same 4700pf disc/500pf doorknobs at the base of the
plate choke. If the B+ cable
with the SHV connector on each end is also shielded, then ur really have all
bases covered. Bond the chassis of
the HV supply, directly to the chassis of the RF deck. If shv connectors and
coax used, that will be the case. I run
10 ga rw-90 between the amp and the mating RF deck anyway.
## That noise you hear on RX is shot noise usually, as described by Bill,
Wa4lav...and very rare.
Later... Jim VE7RF
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