[Amps] Russian tubes GS35b et al.

[MorgusMagnificen at aol.com]

Ian:

       I have been thinking about your original response to my request, and 
realize that I failed to see a good point that (I think) you were making. I 
wish to amend my original response as follows.

       I stand by my judgement about needing actual plate curves to make the 
final calculations and judgements about amplifier performance using a given 
tube. However, I have just realized that the basic inter-relations of PS 
voltage, voltage swing, and output power are really the same as with 
solid-state designs. That is, V-squared/2R still applies. The only difference 
is that our tubes can not be driven into hard saturation but only down to a 
few hundred voltages. As B+ increases, this becomes a small percentage of the 
potentially available voltage swing, so we can still hope to achieve close to 
V-sq./2R.

       In summary, for a given power supply voltage and target output power, 
R is inherently fixed as V-sq./2P. The only thing the tubes curves will tell 
us is that the tube is actually capable of doing it - that is, it can be 
driven to near-saturation. So as a useful rule of thumb for estimating a 
potential amps performance, I fully agree.

       My comments about power gain still stand, however. There are no basic 
rules about the power gain, grid current, etc. These are all unique to the 
physical design of each tube and must be all be determined from the 
documented tube specs. If they are not available, it becomes voodoo (oh-oh, 
there is THAT word again.) I have also heard the 50 ohms Rin  rumor for the 
GS35b, but the power gain figures I hear are all over the place. The Russian 
data sheet shows grid current curves which imply close to 50 ohm at lower 
power levels (<500W) but at 1A. of peak plate current, Rin is dropping like a 
rock.

Eric von Valtier K8LV