HI guys,
Sorry for english,but I do not have Russian keyboard,well,in regard with this issue I can say that parallel work of two tubes is calling for trouble and headache !You will never get expected power,since tubes are not even close in characteristics, especially in terms of the idle current and so on.Push-pull is good way,I would say best way,bit,builder should keep in mind,that with PP PA,there is a lot of third harmonic power,so PP PA MUST be followed with good band pass filter.When I have made 144MHz PP PA with two 4C250A,there was about 30W of power on 432MHz for example.And small observation yet,I have made PA with GI7B,and at power level around 500W out,cathode MUST be culled very good,unless one do not wish unsoldered cathode pin because of really extensive heat,which certainly makes unhappy PA and its owner!