Tony,
Even the old 10-11 meter sweep tube amps had a tuned input, or at least the
better ones of them. They even knew it was better than not having any at all.
Most of those used a tuned transformer feeding either the cathode(s) or the
grid(s). Same thing applies to any amp IMHO.
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/28/05 at 10:57 PM Tony King - W4ZT wrote:
>Tomm Aldridge wrote:
>
>> This is an interesting thread to me not because of the AL-811 vs
>> MLA-2500 but because I am designing and building an amp. If I
>> understand this correctly, using a TS570 transceiver to drive my amp
>> implies I really don't need a tuned input circuit as I can just use the
>> built-in tuner of my rig to achieve a good enough match to the input of
>> the tubes. That saves me money and complexity.
>>
>> However, some on this list advise that the proximity of the output C of
>> the tuned input to the cathode of the PA is very important for its
>> "flywheel" or energy storage effect during the wide swings in impedance
>> during a cycle of operation.
>
>I have gotten the same advice / impressions. A tuned input adjacent to
>the cathode appears to be the only true way to get a good flywheel
>effect. I suppose, if you didn't care about improving the IMD that it
>might not matter. I hope that some of the experts will chime in on this.
>
>>
>> My question is, which strategy should one employ and what are teh pros
>> and cons? Assuming, of course, a built in AT such as in the TS570.
>
>There is a good link at <http://www.somis.org/SB220ci.html> where Rich
>discusses the need for a good tuned input. This article is about the
>SB-220 but the idea is the same. Go to the link and scroll down to
>"Improving Input SWR" about two thirds of the way down. I think that
>will help us understand why it's more complex than matching the radio
>output to the cathode input.
>
>My questions to the group are these:
>How many of those running homebrew amps use a tuned input? How many are
>not?
>Now how many of those running a COMMERCIALLY manufactured amp are NOT
>running a tuned input?
>
>> Regards,
>>
>> KD7QAE
>> Tomm
>> <snip>
>
>73, Tony W4ZT
>
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