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This CV1587, made for the Air Ministry, is a renamed VCR138A. The VCR138A, crown and AM are etched into the glass whereas the CV1587 is printed on. The VCR138A is basically a VCR138 with an improved screen. The Mullard ECR35 is an equivalent commercial type.

It is a three inch CRT with a green phosphor (p1) and fitted with a 12 side contact B12D base. It was used in airborne radar systems as an indicator.

Like the VCR97 faults can occur that are just the wires detaching from the base contacts. Un-screwing the plate on the base allows for the wire to be re-soldered.

The operating voltages are arranged to give the final anode at deflection plate potential of, say, 200 Volts. These leaves the cathode at about minus 1,000 Volts. The heater cathode insulation is poor and the 4.0V heater at 1 Amp would have to be supplied by a separate transformer winding. The deflection is electrostatic. In normal practice A1, A3 and the Aquadag colloidal graphite internal coating are all strapped together.

The Type designation on the neck of the tube.

The B12D side contact base with the gun assembly seen through the clear glass neck.

With the light from one side the curve of the shadow indicates the dome nature of the screen. The technology to allow optically flat faceplates was a post war development. The curve places the glass in compression and allows it to withstand the external atmospheric pressure. The overall diameter of the screen is 88mm.

The end window envelope neck is 62 mm in diameter and, including the B12D base pins, is 335 mm tall.

References: data-sheet & Radio Constructor article.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.