Valve transmitters

This is grounded at the operating frequency, but carries a DC potential, normally 10 to 50% of the plate voltage.

For very high gain circuits, the shielding effect of the screen may not be sufficient to prevent all coupling from the plate back to the grid.

Coupling of energy from the output back into the input can also occur due to poor circuit layout.

It is therefore often necessary to add a neutralization circuit, which feeds some of the output signal back to the input with proper amplitude and opposite phase so as to cancel out the above-mentioned undesirable effects.

A DC bias is applied to the valve to ensure that the part of the transfer equation which is most suitable to the required application is used.

In the RF designs shown on this page between the anode and the high voltage supply (known by convention as B+) is a tuned circuit.

This tuned circuit has been brought to resonance, and in a class A design can be thought of as a resistance.

In short the load formed by the loudspeaker driven via the transformer can be thought of as a resistor wired between the valves anode and B+.