[Amps] GS-35B Efficiency varies with frequency ?

[Behiels JeanPierre]

Regarding this subject ...
I had in the past problems with a try to setup a experimental  amplifier with a twin GS35b tube for HF purpose.
Could not obtain resonnance of output PI circuit for frequencys bove 21 Mhz.
Any solution or experiences on that subject will be mutch appreciated.
Is that also a result of poor efficienty of a couple of twin tGs35b tubes on higher Hambands     
I also made a try with a PI-L network design to transform the anode output C to a higer minimum value especially on 28Mhz where C1 goes to very small values !!
Or did I choose for this experiment only the wrong tubes type for this kind of purpose ?

Jean ON4AEF.