The CY1 is a side contact Ct8 based valve. The CY1 is identical electrically to the CY31 which is on an IO base. This half wave rectifier was designed to operate on universal supplies as it has a 200 mA heater. The maximum reservoir capacitor is 32 µF and the minimum series resistance to limit in-rush current is 125 Ohms.
The Tungsram name has almost been rubbed off of the envelope but the final M and asterisk are just visible.
The usual pattern of a wide anode with a small front to back dimension.
The twin anodes: each has two support rods one in the centre and one on the outer edge fixed to the main supporting rods.
A closer view showing the round cathode tube.
The top mica. This is a half wave rectifier and the two rectifier sections are connected together above the mica. The other examples of the CY1 have a single rectifier section.
The original box is 50 mm square and 140 mm long. The valve was protected by being wrapped in corrugated card with an outer paper wrapper.
Twelve Shillings and six pence plus purchase tax.
The classic envelope is 38 mm in diameter and, excluding the Ct8 base pins, is 87 mm tall.
References: Data-sheet & 1043. Type CY1 was first introduced in 1939. See also1939 adverts.