14R7

The 14R7 combines two diodes and a pentode sharing a common cathode in a glass bulb with an eight-pin loctal base. General Electric describes it as suitable for combined detection, automatic-volume-control rectification and audio amplification; the pentode may also operate as a radio-frequency or intermediate-frequency amplifier. The semi-remote-cutoff characteristic specified by GE allows transconductance to be reduced by increasing negative grid bias, a property relevant to gain control. The manufacturer expressly notes the low coupling capacitance between the diodes and pentode.

The heater is specified for 12.6 V at 0.15 A, on AC or DC. Tung-Sol places the tube in AC/DC receivers using 150 mA heaters. The sources also retain a different nominal indication: the RCA sheet dated May 1, 1950 lists 12.6 V and 0.150 A in the table, with 14 V and 0.16 A identified as nominal values in the notes. These indications must be read in the document's context, rather than mistaken for a second heater section. RCA also relates the 14R7 to the 7R7, distinguishing their heaters.

For the pentode in Class A1, GE tabulates 5.5 mA plate current and 3 mA/V transconductance at 100 V plate voltage, 100 V screen voltage and −1 V grid voltage; raising the plate to 250 V while keeping screen and grid unchanged gives 5.7 mA and 3.2 mA/V. The same sheet's design-center limits include 250 V plate voltage, 2 W plate dissipation and 0.25 W screen dissipation. Maximum screen voltage is 125 V, distinct from the 250 V maximum for its supply. Each diode has a continuous-operation limit of 1 mA: the characterization figure with 10 V applied does not replace that limit.

The base is a locking-in loctal type, not octal despite having eight pins. Viewed from below, the heater connects to pins 1 and 8, the pentode plate to pin 2, the two diode plates to pins 3 and 4, the screen to pin 5 and the control grid to pin 6; pin 7 combines the cathode, suppressor grid and internal shield. Any mounting position is permitted. Documentation consulted: General Electric/Ken-Rad, 14R7, ET-T745, February 1951, four pages; Tung-Sol, 14R7, February 1942, two pages; RCA, summary sheet dated May 1, 1950; Brimar, 14R7 sheet, p. 140.