Hi Wayne,
Everything that you mention is great except that I don't know why you
are involving the complication of a 2:1 step up transformer. Just
design each pi network (one for each band) to have an input impedance of
50 ohms and an output impedance of 100 ohms. Q=2 is just about right.
You're right  using pi networks, you need to switch both the input and
output. I did this with relays having 6 volt coils and wired each input
relay coil and output relay coil in series. Works great. 73, Tim, W2UI
n1wr@chesapeake.net wrote:
> I continue to work on the design/construction of my 41000 amplifier. I'm
> working on the input network details.
>
> The 41000 has a generally accepted input impedence of 100 ohms. So I am
> planning on using a 2:1 step up unbalanced to unbalanced balun followed by
> a parallel tuned circuit, Q of 23, for each band. Taking this approach I
> will need only one relay contact per band to switch each tuned circuit (as
> opposed to two needed to switch a pi network).
>
> In all of my reading and research I haven't seen this approach taken. The
> grid compartment is under construction. Before I go ahead and construct
> the input this way  can anyone come up with a reason this won't work?
>
> I thoroughly enjoy this list and faithfully tune in to the goings on. I
> really appreciate the help and support that is provided.
>
> Wayne N1WR
>
>
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