[Amps] Operating 3-tube Amp With 2 tubes

[Jeff Maass]

We have an old LK-800 amplifier, which was designed to use 
three 3CX800A7 triodes. This amplifier is used as a contest
amplifier over 48-hour periods in a multi-transmitter operation.

We "inherited" this amplifier with the purchase of a house in
the Caribbean. One of the sockets had fallen apart, and one 
tube had failed. It was restored to working order, and we've been 
operating it with just two tubes, with the third chimney sewed (!) 
closed to retain the cooling air pressure.

We're now considering whether to replace  the third socket,
and to add back the third tube. The extra power is *not* required,
as the power limit where the amp is to be used is only 1 KW.
We already have a third tube as a spare, and the SK-1900
socket is cheap, so the additional cost is not a concern.

Is there any reason to replace the socket and tube, from the 
viewpoint of reliability / ease of operation / purity of output? My 
thought are:

The output network was designed for the plate impedance of the
three-tube complement, and tuning will be more certain and within 
the central range of the components if three tubes are there.

We have had TVI problems with neighbors, and as a multiple 
transmitter station, we are always very sensitive to keeping our
output clean.

Are there any possible input network / input impedance issues?

Running the amplifier with three tubes sharing the load will decrease
the heat load on the components, as dissipation from each tube 
is reduced, and airflow would be as designed through each 
base/tube/chimney. Our ambient (input air) temperature is often 
above 90 degF.

Thanks for any comments!

73,
 Jeff Maass       jmaass at columbus.rr.com     Located near Columbus Ohio
         USPSA # L-1192       NROI/CRO    Amateur Radio K8ND
Maass' IPSC Resources:  http://home.columbus.rr.com/jmaass/index.html
Circleville USPSA/IPSC: http://home.columbus.rr.com/jmaass/pcsiipsc.htm