The CY1C from Philips is electrically the CY1 with a B5 base cap fitted rather than the Ct8 base of the CY1.
The CY1, and the electrically identical, IO based CY31, replaced the Ct8 based UR1 and the B5 based UR1C. It is, therefore, interesting to speculate that the CY1C was a replacement for the UR1C. The electrode sizes suggest a similar power rating.
The maximum reservoir capacitor will be 32 µF and the minimum series resistance to limit in-rush current will be 125 Ω.
The CY1, CY1C and CY31 (IO base) were introduced in 1939.
Pinch construction and indirectly heated.
The painted dome carries the identification. Made in England indicates manufacture at a Mullard factory. The gold paint is also indicative of Mullard.
The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 95 mm tall.
References: Data-sheet & 1043. Type CY1C was first introduced in 1939. See also1939 adverts.
