[Amps] Input impedance of pair 3-500z's in GG

[Dan Hearn]

There are a number of reasons to use a tuned input. One is reduced IMD
distortion and there several others. Open any Radio Amateurs Handbook to the
RF Power Amp chapter and you will see a good discussion on the subject.
73, Dan, N5AR
-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
Behalf Of Jerry K
Sent: Sunday, December 14, 2008 8:09 AM
To: MIKE DURKIN
Cc: amps at contesting.com
Subject: Re: [Amps] Input impedance of pair 3-500z's in GG

During the time I owned it, I drove my Swan MK II with Johnson Rangers,
a Kenwood TS-530SP (6146's), a Kenwood TS-450S/AT, a Yaesu FT-900AT, an
FT-1000D, and a few other miscellaneous cats and dogs. It never once
hicupped, nor did any of the above rigs have any problem driving it.
Having been exposed to a few later model fancier amps since then I wish
I had the MK II back. I suppose it's worth noting that all the solid
state rigs had built-in tuners, all of which handled the input of the MK
II just fine. Of course, the Rangers and the TS-530SP didn't much give a
rip what they transmitted into, they just tuned up and worked. :)
73, Jerry W5KP

MIKE DURKIN wrote:
> I didnt know the Swan Mark II didn't have an input matching network, my
only experience is with the SB220 and HL2k witch do have input networks. If
its not needed, then is it to help keep harmonic transmition down while the
input impeadence is not close to 50ohms?? I havea yokogawa P9306UL medical
liner that has grounded grid 3-500z's - are you saying that i can remove the
input network?? I have a FT-450AT that i would like to use with it.
>
>
> Date: Sun, 14 Dec 2008 07:49:31 -0500
> Subject: Re: [Amps] Input impedance of pair 3-500z's in GG
> To: patriot121 at msn.com
>
>
>
>
>
>
>
>
>
> In a message dated 12/13/2008 8:12:32 P.M. Eastern Standard Time,
> patriot121 at msn.com writes:
> Yes,
>   but dosn't the impedance vary wildly throughout the AC wave form??
> Isnt
>   that why the input circuitry is there ... because a solid state
transceiver
>   cant handle the changes....
>
>
> Yes that is true, but one can notice that an amplifier such as a Swan Mark
> II  which has no input matching network can be used with a radio such as a
> Yeasu FT-847 with fairly good success.  For 2 reasons, one is that the 847
> does not fold back on swr as quickly as most other radios ESPECIALLY
ICOM'S and
> two, since the input of the pair of 3-500's is close to 50 ohms the radio
is
> happy.  Even at 85 ohms, the SWR is still tolerable.  But as we know
> there are other reasons why tuned input circuits are advisable.  In
> developing a tuned input circuit, using a fixed resistance as a load to
develop
> the circuit is an approximation, final adjustment will have to be made by
> actually adjusting the input circuit as the amp is being
> driven.
>
>
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