Hi Dick!
According to Ray Heaton -- three feet max!
'73 Dave N7UE
On Tue, 3 Mar 1998, Richard W. Ehrhorn wrote:
> Hi Arturo & all..
>
> You're right - at the time the '78 was designed and for most of its
> production life most transceivers had tuned-output, vacuum tube amps so the
> "flywheel" of a tuned-input PA wasn't necessary.
>
> I think you'll find that the length of drive cable between transceiver and
> amp input can make a big difference. Frankly I can't remember the optimum
> length, but if yours isn't somewhere close to 5-6 feet you might try that
> length of RG-58/U & see what happens. Maybe someone else on the reflector
> knows the optimum length for sure?
>
> 73, Dick W0ID
>
> -----Original Message-----
> From: Arturo Gargarella [SMTP:AGargarella@sipetrol.com.ar]
> Sent: Monday, March 02, 1998 9:28 PM
> To: amps@contesting.com
> Subject: [AMPS] Alpha 78 Input matching unit
>
> I can remember I read in this reflector someone saying "I can?t achieve
> more than 840 Watts with very low grid current (something like 20 mA)".
> I experienced the same on 10 and 15 meters. From 20 to 80 I can run a
> little more than 1 KW.
> I use a TS850 to drive it.
> I think there is a problem with the input matching unit.
> They use a resistor pack which total resistance is about 22 ohms and it
> is in paralell with the input.
> Maybe it was ok at the time the 78 was designed (high output electron
> tubes transceivers) but now with solid state ones there must be some
> changes. I tried giving more output (140 W) to the 850 and I could
> achieve 1 Kw on 10 meters and 1.3 KW on 80 meters. That was only for
> test purposes.
>
> Is that the problem ?
>
> Does anyone know the reason of such input matching unit design ?.
>
> Is there anything to improve ?
>
> Thanks in advance for the help
> 73 de Arturo, LU6ETB
>
>
>
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>
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David B. Ritchie, Esq.
D'Alessandro & Ritchie, P.C. Intellectual Property Lawyers
1731 Technology Drive, Suite 700, San Jose, CA 95110-1312
408-441-1100 (TEL); 408-441-8400 (FAX); N7UE@ALUMNI.CALTECH.EDU
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