G0RUZ Weak-signal DX on 50,144,432 and 1296 Mhz for the Radio Amateur

The Anode Compartment

The anode compartment features a standard Pi L network. Due to the large anode cooler the GS35 has quite a lot of stray capacitance to the chassis. In practice this means that it is difficult to design a tank circuit with a low loaded Q. A low loaded Q is important because if the loaded Q is high then the circulating currents in the tank circuit will be high. High current flow means an increase in resistive losses in the tank circuit and hence poor efficiency.

I have used some silver plated 12mm wide copper strap for L1, this will help keep resistive losses to a minimum. I have also used it for all interconnections so that low loss, low inductance connections have been made wherever possible.

The blocking capacitor is a Russian device and is 680pF, it is a 15kV unit and will carry sufficient current for this application. The tuning capacitor is a 25pF 5kV Jennings unit and the loading cap a 6KV 500pf Jennings unit. 

For the tuning C I feel that a flapper may be more appropriate, this gives lower minimum C allows lower loaded Q. A flapper is also very cheap! I will present an amplifier using this technique at a later date.

The load C is also way over the top, what you actually need is any capacitor with around 200pF and 2.5kV voltage breakdown. A wide spaced air variable would be just as good here. The large Jennings units that I have used were available surplus and so I used them.

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