300mA series-string heater (25V/0.3A) for AC/DC TV receivers. The 'P' prefix in Mullard/Philips nomenclature denotes a 300mA heater string design.
Valve Equivalents database confirms I/O base (Octal with top cap), 25V heater (via 25E5 entry).
Philips interchange lists 25E5 as the American equivalent designation.
Brans Vademecum lists PL81 as equivalent — this is a similar line-output pentode but with different electrical characteristics (EL81-based vs EL36-based).
Electrically identical to EL36 in all electrode characteristics; only the heater differs.
Not interchangeable with EL36/6CM5 without heater circuit modification.
Pin Layout — Octal
1Internal Connection
2Internal Connection (Cathode/Suppressor)
3Heater
4
Socket-Compatible Tubes ⚠ Not electrically compatible