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

On this photograph you can clearly see the tube in the grid block. These grid blocks are available from OZ1GOK and are a very good solution. The block leaves an 8 mm gap between the chassis and the block which allows air to pass through from the pressurized cathode compartment through the anode cooler and into the anode compartment. This cooling arrangement ensures that all the GS35B's electrodes are adequately cooled and minimizes tuning drift.

One side of the heater and the cathode are physically bonded in the GS35B and so bias is fed through the bifilar heater choke. This choke is decoupled with 1nf 1kV feed through capacitors and an additional 1nf 1kV disc ceramic capacitor. The choke presents a high impedance to 50Mhz and any RF that is remaining at the transformer end will be shunted to ground by these caps. This will ensure that no RF gets anywhere near your bias circuitry.

There is an argument that says this arrangement could cause the heater transformer to get hotter as the bias current and the heater current will be flowing through the transformer secondary. In practice this has very little effect with such small currents. Worry about this when you are starting to run tubes with 3 amps of cathode current, then you will also have other "issues"!

The only other thing of note is to try and keep all coils in close proximity at right angles to prevent any coupling.