OK, another question. I'm designing the output network for my amp, and I'm
facing the issue of getting a reasonable Q on 10 meters with practical parts.
The 1999 ARRL handbook has a discussion of this, and they mention putting a
small inductance in series with the plate of the tube, before the pi-net input
capacitor. This has the effect of transforming the plate load impedance to a
much lower value (in their example, from 2200 to 1200 ohms), so that the pi-net
can be designed with a more practical value of input capacity on the higher
bands. The effect of this inductance decreases with frequency, of course, so
you can ignore it on the lower bands. Sort of a "L-Pi" (or L-Pi-L) network!
Recently I was looking at a 30S-1, and I noticed that the plate tuning capacitor
was a big air variable, right next to the shielding. "Collins should know
better", I thought, until I saw the little coil in the anode compartment!
I know this was discussed a few months or a year ago, and I recall that KE9NA
used this in his amp. My question is: what is the downside of doing this? It
looks too much like a free lunch to me.
73,
Vic, K2VCO
Fresno CA
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|