DAF11

The DAF11 is a battery valve combining a controlled audio pentode and a diode. Telefunken specifies direct heating: nominal filament 1.2 V, 50 mA. It is designed for one dry cell, permitting discharge down to 0.9 V; another source, such as an accumulator or mains supply, instead requires ±15% tolerance. All electrode voltages refer to the negative filament end.

Pentode measurement points are distinct from loaded resistance-coupled operation. At 120 V anode, 60 V screen and zero control grid, data give 1.4 mA anode, 0.2 mA screen, 0.6 mA/V transconductance and internal resistance above 0.9 MΩ. At 90 V anode and 45 V screen, still zero grid: 0.8 mA, 0.12 mA, 0.55 mA/V and above 0.7 MΩ. These characterization currents are not those of the loaded audio stage on the same page.

For audio amplification, Telefunken specifies 0.3 MΩ anode resistance and 2 MΩ screen resistance. With 120 V supply and zero grid, actual voltages are 33 V anode and 20 V screen; currents 0.29 and 0.05 mA, voltage gain 85. At −5.5 V grid, gain falls to 28, while anode and screen rise to 101 and 92 V. The stated control ratio is about 3:1. Lower current therefore also changes supply-resistor voltage drops.

At 90 V supply with the same resistors, initial voltages are 24 V anode, 15 V screen, currents 0.22 and 0.03 mA, gain 80. At −4.5 V grid, gain becomes 27 and voltages rise to 78 and 73 V. Curves trace anode current, transconductance and gain as bias varies. A separate diode detector curve uses 30% RF modulation, 0.5 MΩ resistance and 100 pF capacitance, distinct from pentode amplification.

Limits include 150 V operating and 200 V cold anode and screen voltages, 0.6 W anode dissipation, 0.2 W screen dissipation and 4 mA cathode current. Maximum grid-leak resistance is 3 MΩ; diode figures are 50 V peak and 0.2 mA. Capacitances are below 0.02 pF control-grid-to-anode, 2.4 pF diode-to-filament and below 0.002 pF diode-to-control-grid. These are not audio output-power figures: the DAF11 is documented here as a voltage amplifier and detector.

The German eight-contact base belongs to Y8A. Bottom view: 1 screen, 2 control grid, 3 negative filament with metallization and suppressor, 4 pentode anode, 5 positive filament, 6 another negative filament connection, 8 diode anode; 7 has no specified function. The drawing gives body diameter 36 mm, base diameter 43 mm and height above the base bottom 43.5 mm, without marking them maximum. Weight is explicitly maximum 50 g.

Documentation consulted: Telefunken DAF11, Regelbare NF-Pentode mit Diode, sheets 011241, 020342, 030342 and 040342, seven technical pages from 1941–1942 with data, base, dimensions and amplification/detection curves, plus scan index.