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[AMPS] Re: RF choke resonates around 23.4 Mhz errr 22.4

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Subject: [AMPS] Re: RF choke resonates around 23.4 Mhz errr 22.4
From: km1h@juno.com (km1h@juno.com)
Date: Wed, 9 Sep 1998 00:43:31 -0400
Hi Hugo, I've been reading some of the replies with a bit of a chuckle.
The problem with some people is lack of experience and/or unfamiliarity
with the part in question. After a very busy holiday weekend I offer my 2
cents worth.

The B&W 800 was produced for at least 15 years that I know of and was a
mainstay part for the homebrew and commercial market. Several ham
manufacturers used it including the famous Alpha 77 series. I am not
aware of any problem using it on the old 10-80M bands with any reasonable
tube complement. It did not have enough inductance to do an adequate job
on 160 in some situations ( such as the Alpha) so B&W came out with the
801 around 1983.
A word of caution....some hams updated their 77's to the 801 in order to
improve 160 and never ventured on to the WARCS. Anyone buying a 77xxx 
should check which choke they have ( many also went to the 802 later).
The 801 was designed pre-WARC and would explode on 17M. I'm not sure
about the 800 on 12M but I have one here I could test if you are
interested. 
When B&W bought the Viewstar amplifier line and WARC became a reality
they found it necessary to design a new choke. That became the 802 which
now covers all 9 bands from 160 thru 10M. They used the 802 in their
PT-2500A amp.

Unfortunately B&W is now pretty much out of the ham business and will
only reproduce the 802 on special order and a minimum quantity. Even in
that case they ruined the choke by switching from a machined ceramic form
to a Delrin form....YUK !  I have all the specs on the winding and the
machined spacings and only need sufficient interest to try and reproduce
them using a hard Teflon . Unfortunately the person who used to do my
screw machine and lathe work passed away and my limited attempts to find
a new machinist have not been successful.

I do have another choke which I designed for a modified Hunter 2000C so
it would work on 9 bands and have also retrofitted it into the Ameritron
AL-82. Both those amps use a pair of 3-400/3-500 type tubes and I have
not tried it on anything else here yet....others say it works on other
amps. 

Anyway it is:

3 5/8" winding of  #28 single Soldereze close wound on a 3/4" diameter
ceramic form. I use the H.H.Smith #2621 which is a 4" long form..
Series resonances as measured with a Measurements Model 59 GDO and 51J4
receiver for readout accuracy are 15.9, 24.2 and 30.5 MHz . I have run
well in excess of 1500W out on 10 and 12M in the AL-82 with no tuning or
heating problems but I will admit to no testing in the FM wasteland above
29.0MHz. 

I hope this helps a bit.

73  Carl  KM1H
Amplifier Repairs and 6M Conversions Our Specialty



 
On Tue, 08 Sep 1998 11:39:44 -0400 "Hugo W. Catta" <hugo@banet.net>
writes:
>
>
>
>Jon Ogden wrote:
>
>> >
>> >>
>> >>Sorry; I ment to say 22.4 and not 23.4Mhz
>> >>
>> >
>> >?  Hugo - - I would remove turns from the hv rf choke to move the
>> >resonance farther away from any operating frequency.
>>
>> Don't remove too many or it will resonante too close to 28 MHz.  I'd 
>try to get the resonance somewhere around 25 MHz or so.
>
>In that case I´m in trouble with the 12 meters band. I´ll try just 
>23.4 and see if there is any change in the 24.9Mhz tunning.If
>I go higher... I´m sure the Choke´s Q will degrade and might affect 12 
>and 10 meters.
>
>73,
>Hugo
>CX9AAK\W2
>
>>
>>
>> 73,
>>
>> Jon
>> KE9NA
>>
>> -------------------------------------
>> Jon Ogden
>> KE9NA
>>
>> http://www.qsl.net/ke9na
>>
>> "A life lived in fear is a life half lived."
>>
>> --
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>
>
>
>
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>

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