[Amps] TL922 efficiency

[Vic Rosenthal 4X6GP]

I suspect my measurements are incorrect, and possibly someone with 
another TL922 can give me a sanity check.
On 40 meters, I am measuring the following into a dummy load:

Output: 1200 watts (several reliable wattmeters agree).
Drive: 65 watts.
Grid current: 200 ma.
Plate current: 580 ma.
Plate voltage 2600 V under load (3 kV no load).
Zero signal plate current: 140 ma.

This represents an input power of 1508 watts. If I assume that 60 watts 
of the output is fed through from the input, then 1140/1508 = 0.76, or 
76% efficiency. I find this hard to believe. I am wondering whether the 
plate current or voltage measurement is wrong.

My amp has the grids directly grounded, if that means anything.

What do others see from TL922's?

-- 
73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/