[1000mp] MK 5 Driving Amp - a twist?

[Mike Schatzberg]

Hello Rob:

There are a few amps out there with toroidal input.  They still seem to
benefit greatly from the Collins approach.

I am a little confused about the difficulty difference between winding and
installing a toroidal impedance matching transformer, versus cutting a
length of coax.  I would think that you might want to take a little time,
and start with the 23 foot length of coax and prune for lowest SWR.  By the
way, the resulting solution length of coax can be coiled up for convenience,
it does not effect the solution, or the resulting phase shift.

Then if this method fails, you can then redesign the input of your Dentron,
finding room for the toroid, winding it, installing and testing.

Perhaps you could then share the results of the two methods with the folks
on the reflector.

73 and Happy DXing,

Mike
W2AJI
----- Original Message ----- 
From: "Rob Murray" <rmmurray at xplornet.com>
To: <1000mp at mailman.qth.net>
Sent: Tuesday, October 24, 2006 9:58 AM
Subject: [1000mp] MK 5 Driving Amp - a twist?


> I have been following the exciter/amp interface thread with great
interest,
> and have learned a lot from it, thank you all. I have a Mk 5 driving an
old
> Dentron MLA-2500 full power amp, and on reading much earlier in this forum
> that the Mk5 internal tuner did not add much to the process, discontinued
> using that tuner.
>
> This leaves me with pretty much a permanent SWR at the Mk 5 of about 1.8,
> independent of band choice; I haven't worried about it much, but have
> thought it would be nice to get it lower. While the thought of the 20.5 ft
> coax matching section is most interesting, I had been thinking of simply
> winding a toroidal impedance matching transformer (say N1/N2 = 1.4:1) and
> placing it somewhere in the input line of the amp (on the amp input side
> after the bypass relay). This thinking based on the thought (guess?) that
> the amp input impedance is pretty well set by the 100 ohm input swamping
> resistor, slightly reduced by the tube input, ie., about 90 ohms resistive
> (generally), consistent with the Dentron specs in the manual.
>
> Since none of the discussion has considered such a solution, I must be
> missing an important point (or two or more...)
>
> What am I missing?
>
> 73
>
> Robert Murray    VA7RMM
> RR1 S5 C16
> Edgewood, BC    V0G 1J0
> Phone/Fax (250) 269-7698
>
>
>
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