[Amps] Fan for SB220

[Jim Brown]

On 12/17/2010 9:45 AM, Bill, W6WRT wrote:
> I question whether tubes in parallel can radiate RF into each other.
> There is a small amount of capacitance from plate to plate, but the
> voltage at each end of the "capacitor" is the same, both in phase and
> amplitude, so no current would be flowing unless the tubes are
> mismatched for some reason.

Tubes and transistors are like batteries in parallel, sort of.  They 
contain an AC voltage or current generator that multiplies the AC input 
voltage or current by some number that is a function of their 
construction and their bias.  Their equivalent circuit also includes a 
source resistance as well as stray capacitance and inductance. Those two 
equivalent circuits are in parallel with each other. No two tubes (or 
transistors) are perfectly equal in all of those parameters, so the 
mismatch will cause more RF current to flow in one tube than the other. 
Their gains can also be unequal -- that is, the number by which the 
input voltage or current is multiplied -- which makes their voltage or 
current generators unequal, which makes their voltage and current 
sources unequal.

The net effect of all of this is that in any circuit that uses tubes or 
transistors in parallel one can be working harder than the other.  And, 
of course, the combined load on the two tubes or transistors will 
include the R, L, and C of both.

73, Jim K9YC