The SP181 is an RF pentode designed to operate within equipment with a 200 mA heater chain. The operating frequency quoted is 45 MHz which is the frequency of operation of the Pye IF strip used in war time radar receivers. It also fits with Band I television. The introduction date of 1940 suggest it was initially designed for pre-war television receivers. It has a straight characteristic rather than variable μ and pre-war vision receivers were normally of the TRF (Tuned Radio Frequency) type where AGC was not applied.
The reverse is plain zinc paint.
The classic envelope is 32 mm in diameter, and excluding the MO base pins is 80 mm tall.
References: Datasheet, 1040 & 1043. Type SP181 was first introduced in 1940.
Absolute Maximum Operating Conditions¶
Updated March 17, 2014. shape:classic construction:pinch type:pentode age:1940.1950 base:mo heater:200ma pins:8 pin:1.h pin:2.k pin:3.a pin:4.g2 pin:5.g3 pin:6.m pin:7.- pin:8.h pin:tc.g1