[WSWSS] Re: 4-250A question/WTB

[Jack Parker]

Thanks to everyone who replied...good information as usual!

The 4-250's are, essentially, a direct drop-in for the 4-400's. I got 
one response from someone who did the replacement just to see if it 
would work and it did!

The grounded grid configuration that I see in some of the older 
handbooks do ground both the control and screen grids. The newer 
versions use a power zener diode at the center-tap of the filament 
transformer to limit static current. Neither the handbooks (ARRL and 
W6SAI) nor any web sites which I browsed mention any concerns about 
particular dangers of exceeding dissipation ratings of the grids...as 
long as one is aware of the limits and meters the grid current. My amp 
will be cathode-driven to be more compatible with the available drive 
from my 6-meter rig.

There are varying opinions on the stability of the amp, but all my 
resource material cautions about proper design and implementation to 
avoid parasitics. I'll certainly be aware of that problem when the time 
comes.

There were a few suggestions about using other tubes...like the 3CX800, 
but cost is a factor here and, so far, I have zero dollars invested in 
parts. Being in broadcasting and being in the right place at the right 
time in useful :>)

A couple of interesting ideas about chimneys are using appropriately 
modified Ball/Mason jars (quarts for the 250/400's and gallons for the 
4-1000!) or using a Coleman lantern chimney. I love creative ideas like 
that!

Thanks to everyone for the excellent input!

73,

Jack, W7PW