[Amps] Tuned input board on SB-220

[Gary Schafer]

> -----Original Message-----
> From: Roger D Johnson [mailto:n1rj at adelphia.net]
> Sent: Friday, March 24, 2006 2:00 PM
> To: k7rdx
> Cc: garyschafer at comcast.net; amps at contesting.com
> Subject: Re: [Amps] Tuned input board on SB-220
> 
> k7rdx wrote:
> > But if you employ the tuner in the driver, the length of coax to the
> tube
> > cathode becomes another issue. I am confident the engineers at LDG as
> well
> > as those who tested their tuner boards in amps prior to them releasing
> the
> > product for sale,have looked at all the angles,,,All I want to report to
> > this group is the fact the tuner does a great job for me and if it makes
> you
> > happy to question it`s operation then so be it...Jim..K7RDX..
> 
> I'd be a lot more confident if there were some published figures for IMD
> products using an L network vs a Pi network. We really don't need more
> amplifiers spewing out higher levels intermodulation products.
> 
> 73, Roger

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