A War Department marked U52 in the inverted cup getter construction that collectors of this type single out, carrying the broad arrow and a Z code in white on the anode. The U52 is the rectifier the single-ended crowd puts behind Western Electric and very little else.
Tested very strong on a Tesla BM-215A, reading well above minimum with both rectifier sections balanced against one another. The tester has no U52 setting, so the 5U4G card was used, the two being the same valve under different names.
U52 = 5U4G = CV1071 = CV1575 = GZ31 = VU71
Further cross-references in trade use: VT-244, 5Z3P, 5U4GA, 5U4GT. CV575 is the reinforced military specification of the same design.
Read this before you fit it. The U52 will take a maximum reservoir capacitor of 16 µF and requires a minimum series resistance of 180 ohms. Those two figures are not advisory. Exceed either and you will destroy the valve, and a great many rectifiers of this class have been killed by a modern capacitor value dropped straight into an old circuit.
The U52 arrived in 1938 and has spent the decades since acquiring a reputation that few rectifiers can match. It is directly heated, rated at 500 volts on the anodes, and will hand over a hundred watts of DC power with the instantaneous sag-free delivery that only a directly heated design gives you. The envelope is the fat baluster shape with the shaped micanol base familiar from the KT66, forty-eight millimetres across and a hundred and thirteen tall before you count the pins. Among people building single-ended amplifiers it sits in a very short list of the finest rectifiers ever produced, and the GEC version is the one they name.
Two details on this particular valve are worth setting out plainly. The getter is the inverted cup rather than the D getter found on the commoner examples, and dealers who handle these describe that early construction as the sought-after one. The glass carries no maker's name, but it does carry the War Department broad arrow, which is the British government's acceptance mark, and valves taken into service on a commercial specification were often marked with nothing more than that. The attribution to GEC here rests on the construction rather than a printed label, and is offered as my assessment rather than as a certainty. GEC's commercial U52 is more usually seen with a brown base where this one is black, which is unremarkable in itself for service production but is stated here so that you can weigh it yourself.
Broad arrow, inverted cup getter, both sections balanced - if you have been waiting for the right U52, stop waiting.
SKU: 603