[Amps] New Design Question

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Wed, 20 Oct 2010 10:58:11 EDT, TexasRF at aol.com wrote:

> 
>Any comments and criticism will be cheerfully accepted. I don't mind  
>octagonal wheels so much, just don't want square ones!

REPLY:

I don't think you would be successful with only grid current flowing. In
a grounded grid circuit, a large part of the input impedance is created
by "modulating" the cathode current. Take that away and the impedance of
the grid alone is going to be way off. 

I think a better approach would be to use a carbon comp 51 ohm 1/2 watt
resistor temporarily tacked from cathode to ground right at the tube
socket, and then (with the tube in place but no power applied) using a
SWR analyzer such as one of the MJF VHF types to rune the input circuit.
I realize at that frequency the reactance of the resistor's leads is
going to be slightly different from what the tube alone would be but I
think with very short leads you can come close enough. 

Good luck and let us know how it comes out.

73, Bill W6WRT