> -----Original Message-----
> From: Roger D Johnson [mailto:n1rj@adelphia.net]
> Sent: Friday, March 24, 2006 3:36 PM
> To: garyschafer@comcast.net
> Cc: amps@contesting.com
> Subject: Re: [Amps] Tuned input board on SB-220
>
> Gary Schafer wrote:
>
> > You can look in Bill Orr's handbook and he says you need 13 pf/meter of
> > capacitance at the cathode for proper operation. That's 1040pf on 80
> meters.
> >
> > Then figure out what L network values are needed to match the particular
> > tubes input impedance to your 50 ohm driver. In most cases you will find
> the
> > capacitance will fall short of the 13 pf/ meter value.
> >
> > Here is a handy calculator to do it.
> >
> >
> http://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/matching/ImpMatch
> .h
> > tml
> >
> > 73
> > Gary K4FMX
>
> I just typed a msg to George, K6GT, and it occurred to me that an L net
> will not match 50 ohms to 50 ohms. It would seem to me that, if at some
> frequency/loading combination your amp looked like 50 ohms, the LDG
> tuner would go into bypass mode and you would have nothing on the
> cathode side.
>
> Don't get me wrong, I think that this is a terrific idea but LDG needs
> to go one step further and use the freq determining circuit to switch
> in the proper input capacitors to give an appropriate Q.
>
> 73, Roger
Yes Roger, I think the small tuner is a great idea also but with an L
network you are limited to a specific value of L and C that you can use in
order to get a match. The Q is fixed and can not be changed. If you add more
C it will not tune.
73
Gary K4FMX
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