DCH21

The DCH21 is a directly heated triode-hexode frequency converter for battery superheterodyne receivers. Philips Miniwatt distinguishes the hexode mixer and triode oscillator, with triode grid connected to hexode grid 3. Eight available pages include German, French and English data, construction drawing and curves, dated August 1, 1940. Photographs show red-coated Tungsram examples; the data and dimensions retained here belong to Philips documentation.

The filament is intended for battery current and parallel supply, nominally 1.4 V, 150 mA. The ratings page contains a discrepancy: two filament-voltage lines are both printed as maxima, 1.5 and 1.1 V. The second is not arbitrarily changed to a minimum, nor used to derive a guaranteed operating range. The triode alone has typical plate 60 V, grid 0 V, current 2.1 mA, transconductance 1.4 mA/V and amplification factor 28.

The conversion table gives hexode plate supply 90 or 120 V. Combined-screen supply resistors are respectively 15 and 30 kΩ, while the triode-grid–hexode-grid-3 group resistor is 35 kΩ and stated group current 220 µA. At signal grid 0 V and screens 60 V, both cases give hexode plate current 1 mA, screen current 2 mA and conversion transconductance 450 µA/V, or 0.45 mA/V. The table also documents reduced conversion with more negative bias; this is not the triode-alone transconductance.

Hexode limits: plate 135 V maximum, plate dissipation 0.2 W, combined-screen dissipation 0.2 W, cathode current 10 mA, grid–filament resistance 3 MΩ. Screen limit is 70 V at plate current 1 mA, or 120 V below 0.2 mA; these distinct conditions are not merged. Triode limits: plate 100 V, dissipation 0.5 W, grid-group resistance 0.1 MΩ. Grid voltage associated with positive 0.3 µA current is −0.2 V for the respective groups.

Hexode capacitances include input 6.1 pF, output 12.6 pF and signal grid–plate below 0.025 pF. Triode figures: grid–plate 2.3 pF, triode-grid–hexode-grid-3 group input 8.9 pF, plate–filament 2.8 pF. Curves examine plate current, conversion transconductance, internal resistance and oscillator behaviour under their stated supplies. Diagrams labelled K = 1% are not a generic complete-receiver distortion rating.

Octal connections: 1 negative filament, 2 coating, 3 hexode plate, 4 hexode grids 2 and 4, 5 triode grid and hexode grid 3, 7 triode plate, 8 positive filament; 6 has no connection drawn. Hexode signal grid is at the top cap. Maximum diameter 36 mm and maximum height above the pin seating plane including cap 95 mm; pin projection separately dimensioned 14 mm. The 30 mm base-drawing dimension is not assigned to glass diameter. Documentation: Philips Miniwatt, DCH21, Triode-Hexode, Frequency Converter for Superheterodyne Receivers, sheets 438211/1–438218/1, eight pages, August 1, 1940.