Noise can come from the power supply diodes if there is a choke in there. I
built a power supply for a receiver many years ago and I used diodes for the
rectifiers and a choke input filter because the transformer voltage was too
high. I chased the noise problem around for quite awhile. I ended up with
around a .02mf capacitor as the input capacitor and that killed the noise
from the diodes. Had there been no choke in the filter the filter capacitor
would have done the job by itself.
As to resistors and capacitors across modern diodes, it can cause diodes to
be destroyed. Modern diodes have an avalanche area in the reverse direction
that conducts if the reverse voltage gets too high. That will equalize the
reverse current in all the diodes as they are all in series.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Jim Barber
> Sent: Saturday, October 30, 2010 5:42 PM
> To: Fuqua, Bill L
> Cc: amps@contesting.com
> Subject: Re: [Amps] HV rectifier strings - to bypass or not?
>
> Aha - Now that makes sense.
>
> I wonder if Orr possibly just assumed the noise was from the diodes? At
> this point we probably won't ever know.
>
> In most cases these days (and certainly in this case) the tube would be
> biased off when in RX or standby, so no problem, then.
>
> 73,
> Jim N7CXI
>
> On 10/30/2010 3:29 PM, Fuqua, Bill L wrote:
> > The broadband noise is not due to the current thru the rectifieres but
> the shot noise the transmitting tube. If the tube is not biased off during
> receive and you are using an electronic switch or the receiver is not
> entirely decoupled from the output of the transmitter you will get broad
> band noise generated by the random arrival of electrons on the plate of
> the tube. I once had this problem with my EF Johnson Challenger
> transmitter when I was using separte transmitting and receiving antenns.
> It had not solid state diiodes in it at all. Took a while to figure it
> out, I was only a teenager at the time.
> > 73
> > Bill wa4lav
> >
> > ________________________________________
> > From: amps-bounces@contesting.com [amps-bounces@contesting.com] On
> Behalf Of Jim Barber [audioguy@charter.net]
> > Sent: Saturday, October 30, 2010 4:32 PM
> > To: AMPS
> > Subject: [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.
> >
> > My current intent is to use 8 6A10 diodes per leg. The transformer is a
> > 3KV, 2A CCS Peter Dahl and the filter is 32uF by means of two new 16uF
> > 7500V oil-filled caps from Henry Radio via eBay.
> >
> > Opinions?
> >
> > Thanks,
> > Jim N7CXI
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
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