Will Matney wrote:
>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
>
>
Hi Will. We agree that's what "should" be, but that's why we're having
this discussion. The very subject line of this thread and the fact that
the MLA-2500B doesn't have tuned input and the AL-811 does is enough to
verify a great difference in commercially built amps. Not to mention
all the home brew amps that don't have tuned input. I submit that it is
very likely that there are a great many more hb amps without than with
tuned inputs. We are talking amateur bands, HF, amplifiers. That's why I
asked that question. Only answer so far is yours.
But... to Tomm's question, since the three of us agree we should have
tuned input, then we would really like to see, hear and read the in
depth discussion about "why" and "where" tuned input. We all hear those
amps without the tuned inputs, driven to their limits and wider than the
barn door. If you haven't you haven't listened lately. I think it's
fair to seek knowledge about tuned inputs and I don't think that it will
do any of us any good to say they "should" use them without giving good
technical reasons. In trying to understand if the flywheel effect
really does exist to any benefit when using a transceiver's tuner with
some number of feet of coax between it and the amp we may find that it
is ill advised to do so. I don't know but I do want to know.
I have a gut feeling there are a lot of folks that don't want to know
the real answer to this question. Maybe it's because it will make their
amp look bad. That's not really the point but if it does, then couldn't
this discussion help them make it better? I don't want to toss mud and
neither does Tomm, but we, and I'm sure others, would like to see the
subject addressed by our friends here that have a good understanding
and grounding in the subject. There's certainly more to this than an 11
meter sweep tube amp discussion. There are hundreds of amateur HF amps
on the Internet shown without tuned inputs. There are a lot more than
that on the bands that sound terrible when you listen away from the
operating frequency. Of course if it sounds good on your frequency why
should you care about people on either side of you? Maybe that's another
technical discussion ;~)
Just to set things straight, Tomm and I both have two hole GS-35B amps
in construction. My tuned input is in construction. Tomm has a valid
question before deciding what to do with his.
That said... what about it guys? Where are the guys that know about
this subject? I know Rich Measures feels strongly about tuned input
but, Rich, what about that length of coax and tuner issue? Doesn't
sound like a flywheel to me. How's that going to make the amp act?
What do you think? Anyone else? Subject filters on?
Thanks for your time.
73, Tony W4ZT
>*********** 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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