DK192

The DK192 is an RFT heptode for frequency conversion in battery receivers. VEB Röhrenwerk Anna Seghers describes mixer amplification and specifies DC heating at 1.4 V, 50 mA. The filament is directly involved in the electrode system: the diagram distinguishes positive and negative terminals and connects g5 to the positive. Connections or polarities must therefore not be transferred from similarly named tubes without evidence.

The stated operating point has plate 67.5 V, g2 and g4 at 67.5 V and signal grid g3 at zero. It gives plate current 1.2 mA, combined g2/g4 current 3.5 mA and conversion transconductance 0.26 mA/V. Oscillator grid g1 has a 70 kΩ grid-leak resistor and 120 µA grid current. Conversion transconductance describes mixer operation; it is not the voltage gain of a general-purpose audio amplifier.

Limits are separate from operating values: plate voltage 90 V, plate dissipation 0.2 W and g2/g4 voltage 67.5 V. Maximum grid dissipations differ: g2 0.25 W, g4 0.05 W. Maximum cathode current is 6 mA and g3 grid-leak resistance 3 MΩ. Capacitances are 6.2 pF input at g3, 5.2 pF output and less than 0.45 pF g3-to-plate; the last is an inequality, not an exact value.

The base is a seven-contact miniature, classified B7G by archive information. RFT identifies electrodes without numbering contacts: plate, g1, g2, g3, g4, negative filament and positive filament together with g5. The illustrated outline has maximum diameter 16.5 mm, maximum overall length 56 mm and maximum pin length 7 mm; weight is approximately 6 g. The text announces an intention to supply the type later with maximum bulb diameter 19 mm. This planned change is kept separate from the illustrated version and does not prove it had already entered production.

The sheet also addresses miniature-tube fragility: unused contacts must not serve as wiring supports; lateral pressure on pins must be avoided, and socket springs must remain free to move. Insertion and removal must be perpendicular to the socket to reduce glass-cracking risk. These are manufacturer’s practical instructions, not inferred electrical characteristics. Documentation: RFT, VEB Röhrenwerk Anna Seghers, DK192, Heptode für Mischverstärkung, June 1953 edition, two pages. The date identifies the sheet and is not used alone as an introduction year.