[Amps] Drive requirements

[Vic K2VCO]

I am happy to say that I am getting 800 watts out on all bands except 10 m from my grid 
driven class C 2x813 amp at about 1 kw input. I still have to make adjustments to the 10m 
plate circuit.

Now, here's my issue: the drive requirement varies widely from band to band. Here is a 
table of the drive and the grid current I am getting on each band for full output:

Band   Drive  Grid current
160    8 w    28 ma
80     7.5 w  24 ma
40     7.5 w  24 ma
20     17 w   22 ma
15     20 w   24 ma
10     20 w   17 ma

I am using a 6 db attenuator before the input so for example I am setting my exciter to 
80w in order to get 20w drive.

The grid circuit uses powdered iron cores, T106-2 for 160-40, and T106-6 for 20 and 15. 
The 10 meter coil is air wound. Each coil has a link of a turn or two. With the 
attenuator, the SWR on the exciter is close to 1:1 on all bands.

I'm wondering if the variation in drive required is normal, or indicates a defect in the 
grid circuit? I would like to get 28 ma grid current on all bands, and if this is a normal 
characteristic of the tubes, I could just switch in a 3 db attenuator in place of the 6 db 
one on the high bands.

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/