[Amps] Tank value problems and grid current

[chuck]

OK, so I had time last night to play more with my tank circuit. I'm having 2
problems I'm wanting to run by you reflector'ees :)
 
I used several calculators to determine the inductance for the tank on the
amp (gu-84b), running 2100v on the plate
when keyed, about 2300 idle. I have no clue what the current will be at any
given drive point.
 
 
 
I tapped the coil around 3.7uh  and set the caps before installing it to the
values on the spreadsheet..I forget exactly what they were now
but here is what I have been observing. (and I did a 7.2uh coil for 3.8mhz
and observed the exact thing as below)
 
While increasing power in 4-8watts in, making slight tune adjustments to see
if power out increases/decreases
I notice that the screen grid current decreases some and then starts to
increase, (which is ok) now increasing the input to 10w
I notice about 500w out, hold key down I see the screen current start to
drop BUT the output power seems to stay
constant...I'll investigate that some by monitoring both grid voltages but
thought it was weird.
 
Also now at this point while increasing the input power getting up around
1kw the tank needs MORE tune capacitance
and I'm using a 1000pf vacuum cap. spreadsheets were saying around
600-700pf..I run it to the end and the power is still increasing.
when I did this on 3.8mhz, I had band switched in a 1000pf doorknob and it
was asking for more capacitance. Is it just values
adjusting working its way to the promised 1.5kw? (values I put in
spreadsheets)
 
I'm beginning to look at roller inductors and multi wafer band
switches..between little room left and $$ I'm rethinking this
whole issue.. if I don't run this full out, the adjustments will always have
to be varied...
 
All I really would like is 80-15m at this point, adding 160 later if I can
find the components..
 
IF I stop this now its going to sit till the late fall or winter :)
 
so! why is my grid current dropping when key down? and why does it ask for
more load capacitance? related? bad vacuum cap?
 
I measured it but not under power...
 
de KA1MWP