>Subject: [AMPS] Broadband Inputs
>Sent: 3/28/1997 5:12 PM
>Received: 3/29/1997 5:29 AM
>From: Carl, km1h@juno.com
>To: amps@contesting.com
>
...snip,,,
>Let us keep this discusion to GG triodes for a starter. Variations
>between tubes is a given....lets start with one setup..a pair of 3-500Zs
>in GG..or a GG 4-1000 or a 3CX3000. I really dont care, lets get started
>first.
>
There is no such thing as a general coverage input for a Class AB2
grounded-grid (g-g) amplifier---or a 300 mpg carburetor for a 1975
Cadillac.
Everything has a trade-offs and pluses. The plus of a g-g amplifier is
that it needs no adjustable regulated screen supply. The trade-off is
that g-g amps need flywheel tuned input circuits--i.e., discrete tuned
input circuits with a Q of about 2--which is no problem for minimal
frequency excursions, but is sticky-wicket for wide ones.. OTOH, a
continuous-coverage tuned input for grid-driven Class AB1 is simple. All
one needs is a small roller inductor. The tradeoff is that you need an
adjustable regulated screen supply--but for those who can solder and
follow a diagram, this is no problem. A diagram is shown on my Web site.
http://www.vcnet.com/measures
The 723-based screen regulator circuit shown is short-proof, RF-proof
and it is sufficient for 2kV at 200mA. Those who need more current
capability (8973 et cetera) users of can parallel additional TMOS pass
transistors as needed. Since the gate current is zero in such devices,
no driver is needed.
R. L. Measures,ag6k,805-386-3734
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