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Re: [Amps] Amplifier Input Circuit Consultation

Subject: Re: [Amps] Amplifier Input Circuit Consultation
From: Tim Long <>
Date: Thu, 23 Oct 2008 17:59:34 -0400
List-post: <">>
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 wrote:
> I continue to work on the design/construction of my 4-1000 amplifier.  I'm
> working on the input network details.
> The 4-1000 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 2-3, 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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