EB41

The EB41 is an indirectly heated double diode with separate cathodes and screening between its systems. The Philips manual recommends it for FM and television receivers and also discusses broadcast receivers. Separate diodes can perform different jobs in one set: the television example combines detection and DC restoration, while FM limiting and detection are listed radio applications.

Heating requires 6.3 V, 0.3 A, AC or DC. The manual allows series or parallel supply; the Philips sheet dated 10 October 1952 specifies parallel supply. Capacitances are 3.6 pF between anode and cathode of each diode, 4.5 pF between each cathode and the other electrodes, and less than 0.03 pF between anodes. The sheet states measurement without external screening; these definitions are more precise than some brief descriptions.

For half-wave rectification Philips specifies per system: transformer voltage 150 V RMS, output current 9 mA, filter input capacitance up to 8 µF and total anode-circuit resistance at least 300 Ω. These belong to that circuit: 150 V is not peak inverse voltage, whose separate limit is 420 V. Diode current is limited to 9 mA, with 54 mA peak. The ordinary heater-to-cathode limit is 150 V; with cathode positive relative to heater a 330 V peak limit is also given, with maximum components of 200 V DC and 165 V AC RMS.

The application discussion explains low internal resistance in television detection: it permits a low load resistance without excessive loss of the highest modulation frequencies. The illustrated first diode uses approximately 1 kΩ and a 10–20 pF detector capacitor. Two inductors compensate stray capacitances for about 4 MHz bandwidth. The second diode obtains the DC voltage establishing picture brightness; the RC network and connection polarity determine its effect on the following-stage bias.

The manual separately plots single-diode current, detected DC voltage and damping resistance for different loads, rather than one constant internal resistance. An ordinary photograph beside an X-ray also shows that active systems occupy only part of the screen volume. Preserved specimen images reveal the internal metal mesh and variants of the lower envelope.

The base is Rimlock B8A: 1 and 8 heater, 3 second cathode, 4 second anode, 5 screen, 6 first anode, 7 first cathode; 2 is unconnected. Philips gives maximum overall height 60 mm and maximum width 22 mm across the illustrated lower portion. The 1952 sheet adds maximum 54 mm above the terminal plane; the manual instead dimensions terminal projection at maximum 7 mm. Each dimension retains its reference, without adding them to create unstated sizes.

Documentation consulted: Philips EB41 sheets 9393993 and 9393992, 10 October 1952; Philips, EB41 Double diode, pages 53–56 of the preserved manual, data, photographs, X-ray, circuit and curves; Receiving and Amplifying Tubes table, EB41 row; specimen photographs; Precision 660 settings for both diodes.