The only time that I have seen hash from diodes was in a power supply that I
built to power a BC453 receiver with a converter ahead of it. The power
transformer I used had too high a voltage so I used a choke input filter
behind the diodes. The power supply made lots of noise up close. I cured it
by placing a .01 cap as the input filter capacitor. No more diode noise.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Carl
> Sent: Wednesday, March 04, 2009 8:51 PM
> To: amps@contesting.com
> Subject: [Amps] Caps across rectifier diodes test
>
> The tests took a bit longer than planned but I sort of got carried away
> plus had other things to do.
>
> The amps listed below were tested in both standby with just the PS &
> bleeder current, and also keying the relay control line.
>
> Test equipment is a Tek 7704 with an aftermarket 2kV, 100X, 150 mHz
> probe. In order to keep the tests identical I built a string of
> resistors on perf board so I could attach the probe at some point just
> below the probes rating as well as several lower points. Nothing fancy
> and using clip leads to attach the board into the power supplies.
>
> I also substituted a regular 10X 300 mHz probe for the lower voltages
> and looked some more.
>
> Amps tested belong to me or were in for repair or 6M conversion.
>
> LK-500ZC, LK-800C, Alpha 76PA, (2)MLA-2500, DTR-2000L, AL-80A, NCL-2000,
> (2)SB-200, SB-220, HL-2200, Clipperton V.
>
> Rectifiers ranged from the 600PIV Heath, 1N5408's and a couple of diode
> blocks.
>
> At no point and no matter how hard I tried were there any sign of noise
> on the trace that could be construed as diode hash. I retested the
> AL-80A with the factory .01 caps removed and no change.
>
> I next built up a 3 per leg 1N4007 string to replace the 5U4 in a
> vintage HQ-129X on another bench. This uses a 2 stage capacitor input
> filter with 2 chokes. Everything looked fine using a regular probe.
>
> While certainly not a scientific exercise it was the best I could do
> with what was available, and I wasnt sure what I would find, especially
> with a few. The NCL-2000 is a 1963 engineering prototype that Ive been
> using on 6M since 1964; it still has the original Solitron 5KV stacks..
>
> Any comments welcome.
>
> Carl
> KM1H
>
>
>
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