I might as well throw in my 6m input matching experience:
I have an Ameritron AL1500 (uses 8877) converted from hf to 6m a few years
back. This amplifier had the input tuned circuits inside a 4" X 4" x 2"
metal box attached to the back side of the front panel by the bandswitch
mounting hardware.
The conversion removed the bandswitch and input box and replaced it with a
small variable C and new aluminum box installed in the same location as the
bandswitch, using the same 3/8" mounting hardware.
There is a small coax cable coming from the T/R relay to the box and
another small cable from the box to the cathode of the 8877. It all sounds
simple but after about 2 weeks of screwing around with T and Pi circuits I gave
up. The best I could do was maybe 2:1 swr.
I even tried modeling the problem with transmission line software but no
go.
At that point, I installed a smallish 6 turn air wound coil from the tuning
C to ground. Then, soldered the center conductor of the input coax to turn
#2, and the output coax to turn #3. The swr was immediately better and the
tuning C had a nice sharp peak in drive and dip in swr. After a couple of
experimental relocations of the output coax tap, the swr was perfect.
So, what do you call a tapped coil match?
73,
Gerald K5GW
In a message dated 3/23/2010 10:48:59 A.M. Central Daylight Time,
zeitlel@cpr3.navy.mil writes:
I believe Swan/Cubic in the 1500Z model amp used a "T" input network vs
a "pi". Not too many of these were made and are somewhat rare on the
used market. I had one for a short time about 15 years ago. Built like a
tank. Input vswr to the solid state rig was very flat.
Lane
Ku7i
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
On Behalf Of TL_IARC
Sent: Sunday, March 21, 2010 3:16 PM
To: Carl; amps@contesting.com
Subject: Re: [Amps] Tuned Input for G-G 50Mhz amp
Hi Carl,
Thanks.
I thought a "Tee" would be easy to tune outside the amp in real time
(one
cap), and would basically achieve the same result as the "Pi".
Someone elsewhere mentioned better harmonic treatment with the Pi, but I
can't relate to that as I have limited knowledge.
73
Isaac, 4Z4TL
----- Original Message -----
From: "Carl" <km1h@jeremy.mv.com>
To: <4z4tl@iarc.org>; <amps@contesting.com>
Sent: 21 03 2010 16:27PM
Subject: Re: [Amps] Tuned Input for G-G 50Mhz amp
> Pi as it allows a more efficient match as well as a lower Q for a no
tune
> 400-500kHz bandwidth.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: <4z4tl@iarc.org>
> To: <amps@contesting.com>
> Sent: Thursday, March 18, 2010 6:11 PM
> Subject: [Amps] Tuned Input for G-G 50Mhz amp
>
>
>> Hello all
>>
>> Trying to decide between a "Pi" and a "Tee" input circuit, for a
50Mhz
>> single 3-400Z amp.
>>
>> (formerly AL-80A with 3-400Z and not the 3-500Z).
>>
>>
>>
>> Any thoughts please?
>>
>>
>>
>> Thanks in advance, Isaac, 4Z4TL
>>
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
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