EF54

The EF54 is a sharp-cutoff RF pentode with high transconductance, described by Mullard for short waves. Our sources describe it as a high-frequency development of the EF50, with aligned grids to reduce partition noise. In the specimens described, a glass envelope is covered by an aluminum shield; the central locating spigot has a locking groove. The cathode has multiple base connections, described as providing a low-inductance path, an important detail when the connections themselves become part of the RF circuit.

The heater requires 6.3 V at 0.3 A. Mullard's operating point uses 250 V at the plate and screen grid, −1.7 V at the control grid and a 150 Ω cathode resistor: plate current is 10 mA, screen current 1.45 mA, transconductance 7.7 mA/V and plate resistance 0.5 MΩ. Equivalent noise resistance is given as 700 Ω; input resistance, specified at 50 MHz, is 10 kΩ. The latter is frequency dependent: the sheet includes a graph comparing a hot and cold tube.

Mullard specifies a maximum operating plate voltage of 300 V, 3 W plate dissipation, 300 V and 1.7 W for the screen grid and 15 mA cathode current. The separately listed 550 V plate and screen ratings concern their supplies and do not replace the 300 V electrode ratings. Maximum stated operating frequency is 250 MHz, without implying that the characteristics measured at the cited point hold at every frequency. The sheet also gives 6.2 pF input, 4.9 pF output and 0.02 pF plate-to-control-grid capacitance: useful RF design data alongside mounting and cathode connections.