KK2

The KK2 is a directly heated octode converter for battery superheterodyne receivers on long, medium and short waves. It combines local oscillator and mixer, sharing filament and electron stream to save current. Philips presents it in the 2 V series in its 1935 manual. Grid 1 is the oscillator grid, grid 2 its auxiliary anode, grid 4 takes the signal; grids 3 and 5 are screens and 6 is the suppressor. Conversion between received signal and local oscillation produces the intermediate frequency.

The filament requires 2 V at about 0.13 A with parallel battery supply. The documented construction uses European side-contact base P8A and signal grid on a top cap; drawings also identify the external conductive coating. Philips of 7 September 1948 gives maximum height 120 mm and diameter 47 mm. Behind this envelope is the aim of combining two functions without two separate filament loads.

For medium and long waves the 1948 sheet gives main and auxiliary anodes 90 or 135 V, screens 45 V, grid 4 −0.5 V, oscillator-grid resistor 50 kΩ, oscillation 8.5 V RMS. Plate current is 0.7 mA, conversion transconductance 270 µA/V or 0.27 mA/V, internal resistance respectively 2 and 2.5 MΩ. Auxiliary current is 1.6 or 2.2 mA, screens 1 mA. At grid 4 −11 V conversion falls to 2.7 µA/V and resistance exceeds 10 MΩ. Gain control thus comes from biasing the signal grid.

For short waves the same edition uses anodes 135 V, screens 60 V, grid 4 −1.5 V, oscillation 6 V RMS: plate 1 mA, auxiliary 3 mA, screens 1.4 mA, conversion 300 µA/V and internal resistance 1.7 MΩ. Earlier data differ: the 1937 manual gives auxiliary 2.3 mA, screens 1 mA and 270 µA/V for this kind of operation. The 1935 manual instead used screens 90 V and fixed bias −3 V on short waves. These are different editions and choices, not values to combine into an undocumented point.

The 1948 limits are main and auxiliary anodes 135 V, screens 100 V, respective dissipations 0.5, 0.6 and 0.4 W, total cathode current 10 mA, grid-1 resistance maximum 0.1 MΩ and grid-4 maximum 3 MΩ. French Bulletin 30 instead gave anodes 150 V, cathode 11 mA, grid-4 resistance 2.5 MΩ; January 1938 already reduced anodes to 135 V while retaining the latter two limits. Capacitances vary slightly by edition: 1948 gives plate 14 pF, signal grid 10 pF, signal-grid-to-plate below 0.07 pF.

Application notes require tighter oscillator feedback than the mains AK2 octode. The 1937 text and French bulletin suggest grid-resistor current about 100 µA on medium/long waves and 60 µA on short waves, illustrating inductive feedback assisted by about 2500 pF. On short waves grid-4 bias stays fixed to avoid frequency pulling unless special countermeasures are provided. Philips also considers oscillator frequency below the signal and an RF stage for sensitivity and noise, warning against excessive gain and whistles. These details place the converter within a complete radio design with explicitly discussed compromises.