Concerning the metal film resistors, I just tried to measure the inductance of
several
different types of 3 watt 100 ohm resistors that I had, including some that I
had
successfully used in parasitic suppressors. I succeeded in proving that this
isn't easy!
An AADE inductance/capacitance meter shows 12 uhy, which is clearly impossible
unless
these are wirewound (with lots of fine wire)!
Connecting them to an MFJ analyzer showed r close to 100 ohms and x = 0 up to
77 or 80
MHz.for two types. An old one-watt carbon resistor started showing reactance at
about 66
MHz. So I'm guessing that this is mostly due to the lead length, capacitance,
etc. and
that the metal film resistors are no worse than the carbon ones.
On 7/29/2010 5:27 AM, Carl wrote:
> 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
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
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Vic
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