| Definitions |
Type | Designation given by the supplier. It may be found that dots, strokes or dashes are also given but the supplier is not always consistent in their use. |
Description | This gives the normal uses for the valve. However, it does not preclude other uses. |
Filament | These two columns refer to the nominal voltage and current for the filament or heater. Usually, the voltage should be maintained within ±5%. It is bad practice to under-run coated filaments. |
Anode | The anode voltage figure can be misleading. The figure given is usually the maximum recommended, although not necessarily the absolute maximum. For some early valves a range of voltages is given. For output valves the anode and other voltages given is that required for the specified output power.Where two figures are given, these refer to the quiescent current and maximum current |
Auxiliary Grid | Screen grid for tetrodes, pentodes and frequency changers but the inner grid for bi-grid valves. The voltage given is usually that required for normal operation. |
Grid | Control or signal grid for all types of valves. Where a voltage is given, this is usually that required for operation at the stated anode and auxiliary grid voltages.Two figures are given for many of the variable-μ valves. These two figures indicate the likely range of bias for a.g.c. purposes. |
ra | The resistance value given is a nominal figure only and can vary by 2:1 or more over the normal operational range of the valve. |
gm | Mutual conductance (slope) figure given by the manufacturer when measured under the most favourable conditions. In operation the slope is usually considerably lower than this. |
gc | Conversion conductance figure for a frequency changer valve. |
Mu or μ | Amplification Factor. This remains substantially unchanged over normal operating range of the valve = gm x ra |
RL | Resistive load required for the specified output power and is optimized for a compromise between maximum power and minimum distortion. For push-pull valves the figure given is for anode-to-anode. |
PO | Power output for the specified anode load and the anode, screen and control grid voltages.The power output is for a specified level of total harmonic distortion such as 10% (or 5% for push-pull operation). |
RK | Recommended value of the cathode bias resistor for all the other stated operating conditions. Where a grid bias voltage is also given, this should be ignored. |
Base | See separate section which gives an outline drawing for the various base types to be found, together with accompanying tables of connections. |
Year | Approximate year of its introduction in the UK (and may be much earlier in the country of origin for foreign valves). In a few cases an intelligent guess has been made, but for the vast majority of valves the year has been established from advertisements, data sheets and reviews in journals. Even so, there could be an error of up to a year in the date given. |
