My wifes family might equal or beat that Dave. English/Scottish mix from
Newfoundland!
Back in the 60's there was a semi company called Transitron. Their
rejects were literally floor sweepings and buckets of them would show
up
at Meshna's, a local electronics scrap and surplus place. Cheaper by the
dozen for 600PIV stud mount but you would need a small bag full to find
enough that would work at 400V to be of any use. Of course, good ones
were a couple of bucks each then.
The amp tests will be completed soon, got a lot done yesterday. Still
working on my morning coffee.
Carl
KM1H
> ----- Original Message -----
> From: "DAVE WHITE" <mausoptik@btinternet.com>
> To: "Vic K2VCO" <vic@rakefet.com>; "Doug Renwick" <ve5ra@sasktel.net>;
> "Carl" <km1h@jeremy.mv.com>
> Cc: "'Ian White GM3SEK'" <gm3sek@ifwtech.co.uk>; <amps@contesting.com>
> Sent: Wednesday, March 04, 2009 4:42 AM
> Subject: Re: [Amps] caps across rectifier diodes
>
>
> Being a "cheap ham" myself (a Yorkshireman who's half Scottish - and
> they don't come cheaper than that) I bought some Semtech and some
> Thomson rectifier modules from a fleamarket in Germany some years ago.
> I don't think anyone knew what they were. They're way, way over-spec
> for what I need
>
> The RIGHT tool for the job. No worries about series stacking issues,
> no worries about hash, no worries about PIV, fit and forget.....
>
> You pays your money and you takes your choice
>
> cheers
> Dave G0OIL
>
> --- On Tue, 3/3/09, Carl <km1h@jeremy.mv.com> wrote:
> From: Carl <km1h@jeremy.mv.com>
> Subject: Re: [Amps] caps across rectifier diodes
> To: "Vic K2VCO" <vic@rakefet.com>, "Doug Renwick" <ve5ra@sasktel.net>
> Cc: "'Ian White GM3SEK'" <gm3sek@ifwtech.co.uk>, amps@contesting.com
> Date: Tuesday, 3 March, 2009, 8:03 PM
>
> That is only one persons OPINION and is in no way a complete
> explanation.
>
> A capacitor across a single diode will snub the spikes if they
> actually
> exist. A cap across each diode of a string will do nothing except
> hasten
> a possible failure in a marginal string.
>
> Learned PS engineers suggest that with some diodes that a .001 to .01
> be
> placed across the complete string and with another to ground at their
> output to the filter. Different diodes require a different cap value.
>>From what Ive read the 1N5408 isnt a candidate unless it is defective.
> For years cheap hams have been buying hamfest bargain diodes that are
> often reject floor sweepings. The statement offered earlier about
> using
> diodes from the same batch is most valid.
>
> Later today I will test 6 different amps in standby and with keyed
> idle
> current using a 300 mHz Tek scope with HV probe and report back.
>
> In the past I have looked at many amps and PS with that setup with the
> goal of eliminating RF getting to the electrolytics and causing
> premature failure. Something that Ameritrons and Dentrons have in
> common. I have not noticed any diode noise but that doesnt mean it
> wasnt
> there.
>
> Old technology diodes and mercury vapor rectifiers are well documented
> as hash producers.
>
> I suggest that anyone else with similar testing equipment do the same.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Vic K2VCO" <vic@rakefet.com>
> To: "Doug Renwick" <ve5ra@sasktel.net>
> Cc: "'Ian White GM3SEK'" <gm3sek@ifwtech.co.uk>;
> <amps@contesting.com>
> Sent: Tuesday, March 03, 2009 11:35 AM
> Subject: Re: [Amps] caps across rectifier diodes
>
>
>> Doug Renwick wrote:
>>> Sorry? ... on the contrary.
>>> I believe the answer from the archives is "capacitors prevent RF
> from
>>> being rectified in the diodes, and generating harmonics."
>>
>> Here's the complete explanation in that thread from W8JI, who
>> designed
>
>> the AL80A and the
>> SB-1000 (which I have and which has capacitors across 1N5408's):
>>
>> --------------------------------------
>> "1.) The diode is a non-linear component with different recovery
>> times. Let's picture one
>> diode in the string having much faster recovery time. This goes hand
>> in hand with that
>> diode having less voltage breakdown. Slowing the rise time of voltage
>> across that diode
>> (by having the capacitors reactance be much less than the diodes
>> impedance near breakdown)
>> prevents one FASTER diode from taking a big hit in voltage cycle
>> after
>> cycle.
>>
>> 2.) When the diodes do switch, the waveform is not a sine wave. Being
>> non-sinusoidal means
>> the waveform contains harmonics. These harmonics can be heard in
>> receivers, and most ham
>> stations have receivers. Even if the PA does not have to pass CE
>> tests
>> for powerline
>> conducted EMI, why risk generating trash that can affect the
>> receiver?
>>
>> 3.) Bypassing is almost always often less than perfect in high power
>> PA's. Capacitors
>> prevent RF from being rectified in the diodes, and generating
>> harmonics."
>> -----------------------------------------
>>
>> --
>> 73,
>> Vic, K2VCO
>> Fresno CA
>> http://www.qsl.net/k2vco
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
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