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

[Ian White GM3SEK]

Behiels JeanPierre wrote:
>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.

The GS35b was designed for UHF pulsed radar, so there is no question 
about the high-frequency capability of the tube itself. In single-band 
VHF/UHF amplifiers with optimized tank circuits, the efficiency only 
begins to fall off above 144MHz, and the GS35b can still deliver 1.5kW 
at 432MHz.

Good efficiency can only be obtained with fairly high anode voltages, 
around 3.0-3.5kV. The upper limit is largely due to arcing, particularly 
when the off-load voltage rises towards 4kV. But none of that will cause 
a *variation* in efficiency below 30MHz.

Any variation in efficiency in a multi-band HF amplifier has to be due 
to the tank circuits - either at the output, the input or possibly both 
locations together. It certainly isn't due to the choice of tube.


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek