[Amps] Thinking out loud

[Jim Thomson]

Date: Wed, 21 Apr 2010 08:39:07 -0700
From: Vic K2VCO <vic at 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