I have immensely enjoyed the back and forth on this thread. It has reminded
me of things I forgot many, many, years ago as a retired engineer now NFP
manager.
I have built a few amps in my day, mostly on the large side for amateur
radio and small side for broadcast. We always placed the proper matching
before the tube regardless of how it was driven. The whole concept of
placing this amount of line or another to get decent coupling between
exciter and amp is nothing but a lack of proper design and attempts to save
money, on the part of the manufacturer. WOW, now that is a run-on sentence
right there.
Amplifiers that required continuous coverage had a tuned input adjustable
by the operator. Single band and/or multi-band had tuned inputs adjustable
for the specific freqs that would be in use.
One can cut & cut all the coax they want. But, that is just a work around.
As most of these modern SS transceivers have tuners built in, there should
not be fold back power issues in the first place. A tube type could really
give a crap. So, the input SWR for your amp on 10 meters is 2:1----So what?
Maybe 10% loss on a short piece the line? No one is going to notice.
Paul
WD8OSU
On Thu, Jan 15, 2015 at 3:58 PM, Hardy Landskov <n7rt@cox.net> wrote:
> But the Caveat to that is you have no control over the loaded Q in an L
> network. It is a function of load impedances.
> 73 Hardy N7RT
>
> ----- Original Message ----- From: "Roger D Johnson" <n1rj@roadrunner.com>
> To: "Amplifier Reflector" <amps@contesting.com>
> Sent: Thursday, January 15, 2015 10:53 AM
> Subject: Re: [Amps] Amps with high swr question
>
>
> Impedance matching is only one of the functions a tuned input circuit on
>> the input of a GG
>> linear amplifier performs. The other is the "flywheel effect" that
>> smooths out impedance
>> variations that occur during the RF drive cycle. Most autotuners are L
>> networks and do not
>> provide the Q necessary for this function.
>>
>> 73, Roger
>>
>>
>> On 1/15/2015 6:46 AM, Paul Christensen wrote:
>>
>>> "If someone has an amp that has high input vswr, why not break the path
>>>>
>>> between the amp relay and the input to the tube and insert a 200 watt
>>> auto tuner? Between the relay and tube ... not in the receive path.
>>> On the surface, this sounds like a relatively inexpensive way to
>>> retain an otherwise good performing amp. What did I miss ?"
>>>
>>> Several homebrew amp builders have done just that. One that comes to
>>> mind is
>>> the 3CX1500D7 amp made by K8RA (SK). He installed an LDG auto tuner
>>> after
>>> the RF input relay. You can see the tuner board mounted inside the
>>> bottom
>>> corner of his amp. Scroll down to page 7.
>>>
>>> http://www.ldgelectronics.com/assets/discontinued_manuals/
>>> AT-100AMP%20Manual.pdf
>>>
>>> Paul, W9AC
>>>
>>>
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>
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