The Mullard PL820 is a new pentode of the line-output type, designed for use in the EHT generators of projection television receivers. In such generators, an inductance in the anode circuit of a pentode of the line-output type is made to 'ring' at a high voltage by bringing about a sudden change in the anode current. Large negative voltage peaks appear across the valve, and under these conditions there is a possibility that the anodes of some pentodes will emit electrons. This anode emission causes damping of the ringing oscillations and consequent loss of efficiency. The Mullard PL820 has been specially designed to prevent anode emission and it is ideal for applications where negative EHT voltages up to 7 kV appear at the anode.
The PL820, which is on the Noval base, has a heater current rating of 0.3 A, and is suitable for use in television receivers with series-connected valve heaters. Its base connections are the same as those of the Mullard PL81 line timebase output valve.