Date: Wed, 21 Apr 2010 08:39:07 -0700
From: Vic K2VCO <vic@rakefet.com>
Subject: [Amps] Thinking out loud
I already have just about all the parts for my amplifier, which will use a pair
of 813's,
but before I do too much construction I need to settle on the design :-) Since
I only
operate CW I had decided to go class-C, which would easily produce 750-800
watts from
these tubes.
Another possibility is to switch to grounded-grid. I am not sure what the
issues would be
in trying to operate a gg amp in class C. Would I have to do more than just
lift the grids
from DC ground and supply appropriate bias and screen voltages? In particular I
want to
provide a good SWR for my solid-state transceiver, and I don't know what the
input
impedance would look like in class C.
I'm looking for ideas.
Vic, K2VCO
### In the past, I have had 2 x GG 813 amps. Both would do an easy 1100w
out..
in Class AB. Neither had any tuned input either.
## For CW use, I would NOT bias them completely off. If you do, you will
generate
key clix [GG] So, let them idle at 10-20 ma of ZSAC. [GG amps biased into
Class C
will generate key clix.] Eff will be very high, with 10-20 ma of Zsac.
## simple circuit, just bond the screen + grid to the chassis with wide, cu
strap.
813's in GG, and no tuned input, will easily handle the auto tuner from any
xcvr.
Another idea is to use 3-4 x 813's in GG. A pair of 813's has an input Z of
aprx
120 ohms... and aprx 60 ohm's for 4 of them.
## simple metering...just like any other GG amp.
later... Jim VE7RF
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