[Amps] 8877 Max Grid Current

[Peter Chadwick]

Rich said:

>The I^2 x R heating of the grid at 144MHz is probably minimal because 
>gold is a fairly good electrical conductor, and there are over 100 
>grid-bars to share the current burden of 24Arms.  

well, the skin depth at 144 is .216 mil (i.e. .000216 inches). The gold flash is
probably a few microinches, so there's the base grid material to consider, and
its resistance - that's going to dominate. What's the diameter of the grid bars?

Now consider the current distribution even at LF. The capacity per unit area is
pretty constant, but all the current has to come in at one point - the bottom -
so you would expect maximum heating there.

I guess at the end of the day, the question is 'What is the effect of RF grid
current on the heating of the grid?' With the currents we're talking about, is
it negligible? So far, I'm not convinced. It's interesting to look at what
happens in a 4CX1000 at 144MHz: that will have (in grounded cathode) an RF grid
current of 3.26 amps, yet it has a zero watt dissipation rating. So if the grid
has a 0.1ohm resistance, there's one watt of dissipation.....


73

Peter G3RZP