100pf 500V silver micas are about as common as illegal immigrants in the US.
All the major catalog outfits stock them.
Carl
KM1H
----- Original Message -----
From: "Martin Sole" <hs0zed@csloxinfo.com>
To: <amps@contesting.com>
Sent: Wednesday, July 28, 2010 9:12 PM
Subject: Re: [Amps] More parasitic choke questions
> Interesting about how they do the series capacitor arrangement though I
> still wonder if it is making it overly complicated. Silver Mica capacitors
> are about as common as Globar resistors here though so alternatives would
> be
> useful too.
>
> As to the power involved I got to digging around and unearthed an article
> Rich Measures had published in QST of 1989, it's on his website. Is the
> theory/math in that article messed up? It certainly suggests there might
> be
> more than a couple of watts in the R on 10m.
>
> Martin, HS0ZED
>
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Carl
> Sent: 29 July 2010 01:33
> To: Jim Thomson; amps@contesting.com
> Subject: Re: [Amps] More parasitic choke questions
>
>
> ----- Original Message -----
> From: "Jim Thomson" <jim.thom@telus.net>
> To: <amps@contesting.com>
> Sent: Wednesday, July 28, 2010 11:33 AM
> Subject: [Amps] More parasitic choke questions
>
>
>> Date: Wed, 28 Jul 2010 15:11:22 +0200
>> From: "DF3KV" <df3kv@t-online.de>
>> Subject: Re: [Amps] More parasitic choke questions
>>
>> Why is that impossible?
>> On HF the resistor is almost shorted out by the inductor.
>> The power absorbed will be less then 0.5% of the desired HF with a
>> typical
>> amp.
>>
>> 73
>> Peter
>>
>> ### .5% of 1500w = 7.5 watts CCS..which is a bunch. Forget the
>> HF
>
>> power absorbed
>> by the resistor. The poor resistor is already being cooked by the
>> thermal
>
>> heat from
>> the hot anode anyway !
>
>
> ** A single 3-500 is putting out 600-800W so your rating is cut in half.
> In
> addition I disagree with the .5% as its more like .1 to .2% with the
> typical
>
> SB-220 type suppressor otherwise they would have lasted up to 40 or so
> years.
>
>
> I noticed the 10 x 1 meg 2 watt CARBON HV multiplier
>> resistor's on one of my old B+ supplies from the 70's had all risen in
>> value by
>> 34% ! And that 34% rise was only after 3 yrs. I recently checked
>> carbons that
>> I bought new, back in the 70's..still in their wrapper.. and most of em
>> are way on the
>> high side..and were never used.
>
>
> ** I recently got an old Command HF-2500 in for service. Not only were the
> filter caps garbage Nichicons withoutout even a temp rating but the
> metering
>
> resistors for ~ 2700V were three 2W carbons! This is as built.
>
>
>>
>> ## Ok... how does one install the cap that's used to negate the XL of
>> the MOX
>> resistor ? Do u wire the cap in series with the resistor.. then
>> parallel the entire
>> mess with the coil ? . The Drake L4B uses wide cu strap.... no 12 ga
>> wire used.
>
> Lay the coil and resistor side by each (for you Canadians) without
> connecting. Now at both ends install a 100pf 500V silver mica between
> them.
> This works fine with 1-2 (50-75 Ohms for one, double for a pair) of the
> Mouser Xicon 5W MOX. It does absolute wonders for a Clipperton L using one
> resistor. 1200W key down on 10M for 30-40 seconds with no smoke or Chinese
> tube anode color. I use the 5W for everything as some stuff I work on the
> parasitic does get close to the operating frequency (old glass bottles)
> but
> Ive never even discolored them. Ive tried 91 and 120pf with no apparent
> change so its rather non critical.
>
>>
>> ## I used one, real small globar in my hb 3-500z amps from the 70's.
>> The GS35-B
>> doesn't require a suppressor on 6m. The YC-156 doesn't require a
>> suppressor an any band,
>> and neither does the 3CX-3000A7 or 3CX-6000A7.
>
> ** I bet some could get them to take off looking at construction practices
> used.
>
>
>>
>> ## to reduce the plate load Z on the upper bands of a HF amp.. I typ
>> install a
>> .6 uh coil [ 1/4" -3/8" tubing] between plate block caps and input to
>> tune cap. This
>> does not appear to promote instability.
>
>
> ** Not that Ive found even with 2X 4-1000A's at 6KV.
>
> Carl
> KM1H
>
>
>>
>> Jim VE7RF
>>
>>
>>
>>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of Bill, W6WRT
>>
>>> Of course the main L should be very low
>>>loss and the complete suppressor should not absorb any of the desired HF
>>>power.
>>
>> REPLY:
>>
>> Not absorb "any" of the desired HF power?
>>
>> That is impossible and Carl should know better than to make such a
>> statement
>> Bill, W6WRT
>>
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