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Re: [Amps] Checking for IMD

To: amps@contesting.com
Subject: Re: [Amps] Checking for IMD
From: Colin Lamb <k7fm@teleport.com>
Reply-to: Colin Lamb <k7fm@teleport.com>
Date: Fri, 11 Aug 2006 10:43:39 -0700 (GMT-07:00)
List-post: <mailto:amps@contesting.com>
I have been thinking, the last few days, that I should clear off a spot on the 
desk and put my spectrum analyzer and amp on a clean desk and make some tests 
to see what the input circuit does.

I have an old Swan Mark II, which did not come with tuned input.  I added it 
underneath, with small relays and toroids and an additional switch deck.  Since 
it runs 2 x 3-400 tubes, it would be similar to many of the amps out there.  It 
would be relatively easy to switch in and out the input circuit.

As I began thinking about that, it occurs to me that any meaningful test would 
not be that easy.  As soon as I remove the tuned input, the load for the 
exciter changes substantially, which means impedances and drive changes.  Those 
things alone could change the imd sufficiently in the exciter to show a few db 
difference in the imd of the amplifier.  

That would imply that a lot more testing would be required to understand what 
is being tested.  Perhaps one of those class A transceivers would be useful as 
a driver.

Maybe I should just wait until evening and open a beer and forget the whole 
thing.  A test run poorly is not as good as a beer drunk poorly.

73,  Colin  K7FM


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