[Amps] Tuned Input - IMD and efficiency

[Colin Lamb]

I am curious, also.  I have a spectrum analzyer with sufficient resolution to do some testing, if I ever get one of my desks cleaned up.  However, the tests would be fairly specific and it might not be possible to make general conclusions.  

It appears the easiest test would be to take an existing amplifer, with a tuned input, and defeat it.  Then compare the tests with and without the tuned input.  But, once the tuned input is defeated, then external factors start affecting the comparison.  I suspect that without a tuned input, the exciter would be substantially affected, thus endowing the results of the experiment with the qualities of the exciter and length and impedance of the cable.  If that is the case, the results might be close to meaningless.  

73,  Colin  K7FM

-----Original Message-----
>From: Tony King - W4ZT <amps071806 at w4zt.com>
>Sent: Aug 8, 2006 6:47 AM
>To: AMPS <amps at contesting.com>
>Subject: [Amps] Tuned Input - IMD and efficiency
>
>Friends,
>
>There are plenty of claims that it is wise to use tuned input circuits 
>on Grounded Grid amps and that the reasons are reduced IMD, better 
>efficiency and better matching to modern day exciters. It is easy for us 
>to see the matching benefit. There doesn't appear to be any published 
>data to demonstrate the differences of IMD and efficiency in a real amp, 
>or several real amps between using tuned input and not using a tuned input.
>
>Have any of you documented this kind of test before? Have you published
>the data? Would you care to? If you have, would you share it? I have 
>searched the web but have found no published comparison between running 
>with and without a tuned input circuit on a Grounded Grid amp. I don't 
>have the equipment to run this kind of test but it certainly looks like 
>it would be worth while doing.  We could argue theory all day long (and 
>we have!) but a practical demonstration would be worth a thousand arguments.
>
>Obviously it would be more meaningful if tests were done on more than
>one amp but even one good demonstration could prove the point. I would 
>suggest using the same drive power, not overdriving the amp in any case, 
>showing the output power difference and the IMD difference between the 
>same amp with and without the tuned input circuit.
>
>Anyone care to comment, run the tests or offer their data?
>
>Thanks and 73,
>Tony W4ZT
>
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