DK22

The Philips Miniwatt DK22 is an octode frequency converter for superheterodyne receivers. The preserved characteristics are tentative and dated 12 March 1941. Direct heating is specified at 1.2 V, 50 mA; batteries, DC mains or rectified AC mains and parallel or series filament supply are covered. Secondary figures of 1.25 V and 1.4 V do not replace this Philips version’s value. Grids g1 and g3 are internally joined; g4 is the signal grid, while g2 participates in the oscillator section. The diagram shows oscillator and mixer integrated into one tube.

At a 90 V plate supply, the sheet specifies a 12.5 kΩ g2 feed resistor, a 35 kΩ grid-leak resistor for g1+g3 and 200 µA current in that group. With g4 zero, g2 60 V and g5 90 V: plate current 1.5 mA, g2 current 2.4 mA, g5 current 0.25 mA, conversion transconductance 500 µA/V and internal resistance 1.25 MΩ. At g4 −6 V, conversion transconductance falls to 5 µA/V and internal resistance exceeds 10 MΩ. This is the stated 100:1 conversion control, not an audio voltage gain of one hundred.

The second configuration uses a 120 V plate supply, a 25 kΩ g2 feed resistor and a 120 kΩ g5 resistor. The g1+g3 group retains 35 kΩ and 200 µA. At g4 zero, g2 is 60 V and g5 90 V; the same currents of 1.5, 2.4 and 0.25 mA accompany 500 µA/V conversion transconductance and 1.5 MΩ internal resistance. At g4 −8 V, g5 reaches 120 V, conversion transconductance is 5 µA/V and internal resistance exceeds 10 MΩ. Separately, oscillator characteristics at plate 90 V, g5 90 V, g4 zero, g2 60 V and g1+g3 zero are g2 current 2.9 mA, g2-g1 transconductance 0.8 mA/V and amplification factor 8.5.

Limits include plate voltage 135 V, plate dissipation 0.3 W, cathode current 5 mA, g2 voltage 80 V and g2 dissipation 0.3 W. For g5, the sheet distinguishes 135 V at plate current below 0.5 mA and 70 V at approximately 1.5 mA, plus maximum dissipation 0.05 W. This reveals a conflict in the tentative document: its application table gives g5 90 V at plate current 1.5 mA, while the separate limit is 70 V at that current. These figures are not arbitrarily reconciled or offered as a validated design. It also gives maximum grid-leak resistance 3 MΩ for g4 and 0.1 MΩ for g1+g3, and maximum g4 voltage +0.2 V at grid current +0.3 µA.

Capacitances describe isolation between sections: plate-g4 below 0.001 pF, plate 10 pF, g4 15.6 pF, g1+g3 group 5.5 pF and g2 4.5 pF; g2-g4 below 1.2 pF and g1+g3 to g4 1 pF. Filament batteries may start at a maximum 1.5 V, with operation down to 0.9 V. In series chains supplied from DC or rectified mains, current must be set to 50 mA with fluctuations no greater than ±3%. Graphs cover currents, conversion, internal resistance and signal levels under specific conditions; their axis endpoints are not universal limits.

Archive information classifies the base as Loctal B8G. Philips’ drawing does not number contacts; it shows, among other connections, the g1+g3 group and negative filament joined to screen and g6. No pin number is assigned to the unlabelled contact. Illustrated maximum dimensions distinguish a 29 mm bulb, 33 mm base and 60 mm body above the base plane. The lower 15 mm projection including the central key remains separate; it is not added to invent an overall length. Documentation: Philips Miniwatt, DK22, tentative data dated 12 March 1941, eight scanned pages including characteristic graphs and a reverse showing the preceding page through the paper.