12AC5

The 12AC5 is a remote-cutoff RF pentode with indirectly heated cathode and eight-contact Rimlock base. The preserved Philips document refers to JETEC release 1526 of October 10, 1955. Its variable-slope behaviour is shown by anode-current and transconductance curves against grid bias: increasingly negative control voltage progressively reduces amplification sensitivity under the stated curve conditions.

The characteristic point uses anode 200 V, screen grid 116 V and control grid −3 V. Anode current is 7.2 mA, screen current 2.1 mA, transconductance 2.3 mA/V and anode resistance 1 MΩ. The document gives about −34 V grid bias for transconductance reduced to 23 µA/V, a reference distinct from full sensitivity. The two graphs also show the effect of screen voltage and screen supply through a 40 kΩ resistor.

Design-center maximums distinguish anode supply 550 V from actual anode voltage 250 V: the former does not permit 550 V at the electrode. Maximum anode dissipation is 2 W and cathode current 10 mA. Screen supply is likewise limited to 550 V, while the table gives electrode voltage 250 V for anode current below 4 mA and 150 V at the 7.2 mA anode-current reference. Screen dissipation is limited to 0.3 W, grid-circuit resistance to 3 MΩ and heater–cathode voltage to 150 V.

The heater requires 12.6 V, 0.1 A. Stated capacitances are anode–control grid 0.002 pF, control grid–heater 0.05 pF, input 5 pF and output 7 pF. Small direct grid–anode capacitance is distinct from input and output capacitances; these must not be added or substituted without considering the measurement circuit.

B8A Rimlock base is designated E8-30, connection 8GW: 1 and 8 heater, 2 anode, 3 and 4 internal connections, 5 screen grid, 6 control grid, 7 cathode with suppressor grid and internal shield. Internally connected terminals are not spare contacts. Any mounting position. The document gives metric maximum dimensions of overall length 60 mm, seated height 53 mm and diameter 22 mm; its printed imperial figures are preserved separately in the dimensional records. Documentation: Philips, Tube Type 12AC5, from JETEC release 1526, October 10, 1955, three pages of specifications and curves.