DAF96

The DAF96 combines a diode and an audio-gain pentode in a miniature tube for battery-powered receivers. The Philips sheet presents it as an audio-frequency amplifier; Mullard specifies that the pentode is intended for voltage amplification. The diode provides a separate section in the same envelope, with its plate located at the negative end of the filament according to both sheets. It is thus a component for detection and for handling the audio signal before the output stage, not an output power tube.

The filament is directly heated and supplied with direct current. Philips specifies 1.4 V and 25 mA in parallel, or 1.3 V in series; Mullard specifies 1.3 V and 24 mA for series operation. This difference must be respected when designing a filament chain. For the pentode section, Mullard gives a characteristic point with 67.5 V on the plate and screen grid and −1.5 V on the control grid: plate current is 170 µA, screen-grid current 55 µA and transconductance 170 µA/V. This is a measurement point for the pentode, distinct from circuit examples with load resistors.

The application tables show the DAF96 as a resistance-coupled audio amplifier, both in pentode connection and with the screen grid tied to the plate for triode operation. For example, in the first arrangement Mullard gives, with an 85 V supply, a 1 MΩ plate resistor and a 1 MΩ load in the following circuit, a voltage gain of 55 and 5 V rms output at 2.5% distortion. Changing the resistors also changes gain and distortion: that figure does not describe every receiver. Limits for the pentode section include 90 V on the plate in operation, 30 mW plate dissipation and 250 µA cathode current. A Mullard note adds that, under its specified input and output conditions, no special precautions against microphony are needed; this is not a general guarantee for every installation.