[Amps] GS23B Plate load resistance for HF

[Carel, pc5m]

Hi Dave, you might give my "RF Tube modeller" application a try. It will
easily calculate a.o. efficiency, Rload and other parameters. All based on
the constant current graphs as provided by the manufacturer and bias
conditions you can prescribe. See: http://www.pc5m.net/projects/rftubemodel

By the way I am running this tube in a 70cm cavity for contest operation,
output over 1000W. Very nice tube !.

73's Carel.

p.s. Have been cooling this tube for years with a fan blower mounted
"backwards",i.e. sucking air out of the cavity...see another recent message
thread on this reflector... compact construction and adequate cooling.

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Dave Trainor
Sent: maandag 28 oktober 2013 18:55
To: Amps reflector
Subject: [Amps] GS23B Plate load resistance for HF

I am attempting to calculate the Pi-L tank values for a GS23b HF amplifier I
am building and I am a bit confused. I know this tube is usually used at VHF
and above but OM power does use one at HF and I happen to have several of
them I would like to use. I need to somehow know the efficiency, I Think,
and either the info for this usage is missing on the data sheet for the tube
or I am not experienced enough to figure it out.

Using a spreadsheet I got from G3SEK. I am using the following values, 3000V
on Anode, max of 1A DC anode current and planning on getting 1500W output,
using a K factor of 1.5. So the implied efficiency is 50% and a plate load
of 2000 Ohms, all well and good but 50% seems low and I would think I would
be closer to 60%. If I guess at 61% efficiency then the plate load is 2440
ohms and I would at 3000v/1A be running 1830W output.
Then to play with this some, if I put in 3000V/.890A and assume the same
1500W out the plate load is 2247 ohms at 56% efficiency, that changes the
second calculation to 55% efficiency with implied output power of 1469W and
2200 ohms.

Is it safe to assume the 2.2K plate load is close enough?

I am missing something here in knowing how to use the calculations and
spreadsheet correctly. This is not one I want to learn by making mistakes
with HV and expensive vacuum caps.

I can't seem to find anything to help me know what the efficiency
would/should be.

73,
David Trainor
N8ZFM

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