Agreed, cost is an issue for the manufacturing world as it is for
individuals but this isn't about the cost.
Once again, back to Tomm's question: I believe it is not a good idea to
depend on a rig's inboard tuner to match the input of the amp through
some length of coax. I don't think there is any flywheeling going on
through that length of coax and as a result there is poor IMD
performance and poor efficiency. Of course no one else has expressed an
opinion on that question so I may be the lone soul that feels this way.
73, Tony W4ZT
Will Matney wrote:
>Tony,
>
>The very reason they don't have them is cost. They build the amps as cheap as
>possible to make the most bux. For amateur amps, this means an extra
>bandswitch and a tuned circuit for each band. The way most manufacturers see
>it, leave them out and let the transceiver tune to it. Thus, more money in
>their pockets. That's just my opinion on the subject and might be wrong.
>
>Best,
>
>Will
>
>*********** REPLY SEPARATOR ***********
>
>On 3/29/05 at 2:40 AM Tony King - W4ZT wrote:
>
>
>
>>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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>>>>
>>>>
>>>>
>>>
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