UB41

The UB41 is an indirectly heated double diode with separate cathodes, intended for signal detection. The Philips manual describes its properties and applications as identical to those of the EB41, with the heater distinguishing the two types. The UB41 heater is designed for a 100 mA series supply, AC or DC, at a nominal 19 V. Related detecting systems therefore do not imply identical heater supply requirements.

Both systems have separately accessible anodes and cathodes, with an internal screen brought to the base. For the cold tube Philips specifies 3.6 pF between anode and cathode of each diode, 4.5 pF between each cathode and the other elements, and less than 0.03 pF between the anodes. These are different connections, not alternative values of one quantity. A manual photograph also shows the electrode assembly with envelope and screening cage removed, helping reveal the structure hidden by the mesh in complete specimens.

For each diode Philips specifies maximum peak inverse voltage 420 V, diode current 9 mA and peak current 54 mA. The two currents are not interchangeable: one is the diode-current limit, the other the peak limit. Preserved curves cover forward conduction, alternating input voltages with different loads, and relationships between RF signal, detected DC voltage and detector input resistance. The sheet updated on 2 February 1958 refers to EAA91 curves; the manual instead refers to the EB41 description.

Heater-cathode insulation needs particular attention. With cathode negative relative to heater, the limit is 150 V; with cathode positive, the peak limit is 330 V, together with maxima of 165 V DC component and 165 V RMS AC component. External resistance between heater and cathode must not exceed 20 kΩ. Thus 165 V must not be treated as a general anode-voltage rating: it belongs to a specific insulation condition.

The base is eight-contact Rimlock B8A. The Philips drawing assigns 1 and 8 to heater, 3 to second-diode cathode, 4 to its anode, 5 to screen, 6 to first-diode anode and 7 to its cathode; contact 2 has no connection shown. The 1958 outline gives maxima of 60 mm overall, 54 mm from contact plane to top and 22 mm across the illustrated lower portion. The manual additionally shows a maximum 7 mm for the indicated lower section, a separate dimension rather than body height.

Preserved photographs document Philips Miniwatt and Mullard specimens, with mesh screening and different lower-envelope finishes. Measurements of individual specimens do not replace manufacturer maxima. Documentation: Philips UB41 sheet 9394646, 12 December 1953, with plates A–D; Philips UB41 sheet 9382871, 2 February 1958; Philips technical manual, UB41 chapter, pages 189–190; receiving and amplifying valve table, UB41 row; specimen photographs.