[Amps] MLA-2500B Question

[Tony King - W4ZT]

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