[Elecraft] 100 Watts or 500 Watts

[Vic K2VCO]

My approach to the harmonic problem is to use a link-coupled antenna tuner on 80-30 meters 
(Johnson Matchbox), and a homebrew parallel tuned circuit on 160. On the higher bands, the 
simple pi network should be adequate to keep the harmonics down. You could use a pi-L 
configuration on the low bands if you wish.

A bigger problem with class-C is how to keep the high bias from sharpening up the 
beautiful K3 keying and producing clicks. My approach is to have the QSK circuit drop the 
bias below cutoff when the amplifier is keyed, so that the amplifier is initially 
operating in the linear part of the curve. There is a resistor in the grid circuit which 
supplies the remainder of the class-C bias from rectified grid current. But that bias 
rises along with the drive. The bypass capacitor and this resistor form a filter which 
keeps the transition to full power clean.

On 12/22/2010 9:20 AM, Ron D'Eau Claire wrote:
> Time to dig out some old ARRL Handbooks from the 60's. My '62 Handbook has a
> nice 813 grid driven amp that runs Class C for CW and AB2 for SSB, the
> famous "one band kilowatt" amplifiers using a pair of 813's (each band had
> its own RF 'deck' with a common power and metering circuit so each amp could
> be pre-tuned and ready to go at the snap of a relay or switch) and a
> Kilowatt grid-driven 4-400A amp, in addition to the usual assortment of
> ground grid amps.
>
> A builder today may need to 'beef up' the pi-network output filter to meet
> modern spurious emission standards (typically for the second harmonic) or
> use an outboard half-wave filter for each band for that purpose.
>
> Ron (radios should glow in the dark) AC7AC
>
> -----Original Message-----
> On 12/22/2010 11:30 AM, a lister wrote:
>
> Grounded-grid is not the only way to design a tube amplifier. Although a
> traditional grid-driven circuit is a little more complicated, it's one way
> to get more gain.
>
> Amen to that. When I was little, "grounded grid" was vaunted as the way to
> use triodes without needing neutralization, even though one took a real hit
> on gain. Unfortunately, the old-time big amps that use/used several triodes
> in parallel in grounded grid still have a tendency to "take off."
>
> The 813 and the various Eimac ceramic tetrodes are wonderful tubes, and if
> one can go high voltage low current, they are excellent performers. Again,
> when I was young, solid state devices wouldn't function in the VHF/UHF
> region, and the 4CXnnn series were practically a necessity. Need I refer to
> the beautiful amps vended by one of the early moonbounce guys?
>
> I for one would like to see designs using these tubes. Not all of us need
> linear/linearized amps.
>
> John Ragle -- W1ZI

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/