What I am getting at is the 11 meter amps needed all the power they
could get for drive as there was only a few watts available usually.
With a ham amp there is usually plenty of drive available and usually
some means of matching. i.e. antenna tuner, tube finals etc.
Some of the tubes used in the ham amps at the power levels designed for
provided a near 50 ohm match without a tuned input. So they got away
without one.
As a note on tuned input circuits at the tube cathode, as another poster
mentioned "the amp is in series with the driver". All the rf plate
current of the amp has to go through the coax to the driver. It also has
to go through the driver matching stage if there is no tuned circuit at
the amps cathode. Any length of cable between the amp and driver tuned
circuit can provide an unwanted impedance transformation. The Q of the
matching circuit at the driver may or may not be ideal for what is
needed at the amps cathode.
73
Gary K4FMX
Will Matney wrote:
> Gary,
>
> That's the whole point. An amateur amp ought to be designed so it gets
> maximum power transfer too! It's kinda bad that the 11 meter guys did it and
> a lot of amateur amp manufacturers were too tight to do it. One thing, this
> cant be said about Heathkit, they did add them and a very few others.
>
> Best,
>
> Wil
>
> *********** REPLY SEPARATOR ***********
>
> On 3/29/05 at 11:26 AM Gary Schafer wrote:
>
>
>>I don't think most 11 meter amp manufacturers are to concerned about
>>inter mod. The tuned circuit is there to transfer maximum power from the
>>50 ohm radio.
>>
>>73
>>Gary K4FMX
>>
>>
>>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
>>>
>>>*********** 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
>>>>
>>>>_______________________________________________
>>>>Amps mailing list
>>>>Amps@contesting.com
>>>>http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>>
>>>
>>>_______________________________________________
>>>Amps mailing list
>>>Amps@contesting.com
>>>http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
>
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|