The input impedance of a single GS35B is much lower then that of pair of
3-500Z
73
Peter, DJ7WW
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Paul Baldock
At 09:21 PM 12/22/2012, Jim W7RY wrote:
>Did you try 2 pieces of RG58 in parallel? What made you decide on 3
pieces?
W8Ji recommended low impedance coax. 3 pieces is lower than 2 and I have the
room
It seems just one piece of coax that's only 8" should work fine. It
certainly does in my SB221. Maybe there something strange with the GS-35B. I
notice that the Cathode input impedance varies greatly when the Plate is
even slightly off tune, so maybe the the GS-35B needs more swamping than
your typical setup. I'm just guessing of course.
- Paul
>-----Original Message----- From: Paul Baldock
>Sent: Thursday, December 13, 2012 12:43 PM
>To: Carl ; amps@contesting.com
>Subject: Re: [Amps] GS-35B Efficiency Varies with frequency?
>
>Problem is solved:
>
>Originally I had about 8" of RG-58 between the PI input and the
>Cathode. I thought this would be short enough.
>
>After reading info from W8JI's web site I now have 3 pieces of RG-58 in
>parallel from the PI input to the Cathode. I also moved the 10M cap and
>put it right on the Cathode, and compensated by reducing the cap for
>all other bands.
>
>Efficiency is now better than 60% on all bands and about1300W PEP
>output on all bands with 70W (of dits) drive and around 3.1KV on the
>plate
>
>For those that asked, the reason the plate Q is high on the WARC bands
>is that I am using the next higher standard band for double duty so I
>have less inductance than would be ideal. There is not enough position
>on my switch to do it correctly
>
>Thanks for all the suggestions.
>
>- Paul KW7Y
>
>
>
>
>At 08:02 AM 12/13/2012, Carl wrote:
>>That is characteristic of a tired tube and the poor PS regulation
>>doesnt help.
>>
>>Carl
>>KM1H
>>
>>
>>----- Original Message ----- From: "Paul Baldock"
>><pbaldock@frontier.com>
>>To: <amps@contesting.com>
>>Sent: Monday, December 10, 2012 7:50 PM
>>Subject: [Amps] GS-35B Efficiency Varies with frequency?
>>
>>
>>>I am building a GS-35B amplifier. The efficiency drops off a lot
>>>between 80M and 10M. Although the gain is quite constant. Does any
>>>body have suggestions as to why this is or whether this is typical.
>>>
>>>The input PI network has a Q of around 2. The PI output has a Q
>>>between 10 and 20
>>>
>>>Here's some results with 70W Drive:
>>>
>>>3.80MHz. Q=10, Output Power 1.1KW, Vp 3000V, Ip .54A, Ig .26A, Eff
>>>68% 7.10MHz. Q=13, Output Power 1.1KW, Vp 3000V, Ip .60A, Ig .28A,
>>>Eff 61% 10.1MHz, Q=20, Output Power 1.0KW, Vp 2900V, Ip .68A, Ig
>>>.30A, Eff 51% 14.2MHz, Q=13, Output Power 1.1KW, Vp 2900V, Ip .70A,
>>>Ig .29A, Eff 54% 18.1MHz, Q=16, Output Power 1.0KW, Vp 2850V, Ip
>>>.78A, Ig .31A, Eff 45% 21.2MHz, Q=13, Output Power 1.0KW, Vp 2800V,
>>>Ip .82A, Ig .37A, Eff 43% 24.9MHz, Q=19, Output Power 1.0KW, Vp
>>>2850V, Ip .79A, Ig .35A, Eff 44% 28.5MHz, Q=16, Output Power 1.1KW,
>>>Vp 2750V, Ip .85A, Ig .38A, Eff 47%
>>>
>>>You will note as efficiency goes down the Grid current goes up (in
>>>general) for the same drive. Is this normal?
>>>
>>>Things I have tried:
>>>
>>>1. Checking that the bias voltage is not affected by RF. No signal
>>>Vp=3600V, Ip=140mA, Vb=34.5V.
>>>2. Rebuilding 10M PI Output in a different configuration. (It is
>>>actually an L-PI) 3. Checking that the metering is not affected by RF
>>>
>>>Any Suggestions?
>>>
>>>What is a safe Max Ig for the GS-35B?
>>>
>>>Thanks
>>>
>>>- Paul KW7Y
>>>
>>>_______________________________________________
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>>>Amps@contesting.com
>>>http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
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>
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