Thanks to all for the good ideas, guys.
Carl's suggestion of putting 4700pf across each leg is one of those
elegant ones... The point of overbuilding (in this case with a YC156) is
long-term reliability. Touches like MOV's from each leg of the mains to
ground, a 50-ohm 100-watt glitch resistor and now the 4700pf caps across
each leg of the bridge are what help keep the cabinet screws from coming
out and all the smoke and hair-raising "bangs" contained.
The multiple-path bypass caps are something I learned about many moons
ago with medium-power VHF AM rigs, (at Ft. Gordon, GA for useless trivia
buffs) but really hadn't considered at HF.
Now for Multronics aka Cardwell aka Viking to get the roller built
before I expire from impatience. 10 weeks seems like a long... time... !
73,
Jim N7CXI
On 10/30/2010 5:58 PM, Jim Thomson wrote:
> 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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