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(Left) The Mullard TDD4 duo-diode-triode and (right) the new Pen4VA showing the electrode assembly.
Class B valves formed a prominent feature of this exhibit, and the PM2B is rated for working with a 14,000 Ω load impedance. The PM2DX is recommended as a driver, and an input of 3 Volts RMS to this valve is sufficient fer full output. In the AC range, screened HF pentodes have been introduced, and the SP4 is of the non-variable-μ type, and is intended for use as a detector-oscillator, an HF amplifier, or a detector. The VP4 is of the variable-μ type, and is rated for 100 Volts screen potential, with which it has a grid base of about 40 Volts; by reducing the screen potential it may be used as a short-base type valve.
A duo-diode-triode, the TDD4, is intended chiefly for automatic volume control purposes, and there is a single-diode tetrode, the SD4, for which numerous applications can be found, particularly in obtaining QAVC. A new indirectly heated output pentode, the Pen4VA, is rated for an output of over 3 Watts, with an anode current of only 32 mA, while the AC044 has been modified for use with 250 Volts anode supply, and will now give an output of 2½ Watts.
A range of DC mains valves has been introduced; HF pentodes of the ordinary and variable-μ types, a triode detector, and a pentode output valve all have heaters rated for 20 Volts at 0.18 Ampere, while the duo-diode-triode is rated for 25 Volts at the same current.
A wide range of HT rectifier valves was also shown.
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