Same filament (10V/3.25A), same base, same 100W Pa (Class B/C) and mu (~12) — the 242C is essentially a 242A redesign in the same performance class as the 211 but with a different plate structure
242A
Earlier version with original plate design — same electrical ratings but different physical construction
242B
Variant in the 242 family — different plate rating or construction details
Electrical Specifications
Absolute Maximum
Anode Dissipation (max)Plate Dissipation (max, Class B/C)100W
Typical Operating
Amplification Factor (μ)Amplification Factor12—
Heater
Heater VoltageFilament Voltage10V
Heater CurrentFilament Current
Notes
DHT tube: the thoriated-tungsten filament serves as the cathode; there is no heater-cathode isolation.
The Jumbo 4-pin bayonet base (RCA basing 4AZ) is the same large base used on the 211 and 845.
ML-242C is the Westinghouse designation; GL-242C is the GE designation.
Radiomuseum notes: '242A with redesigned metal plate, retaining the same 100W dissipation as 211.'
Pa_max is 100W for Class B and Class C service; derate for Class A₁ CCS operation (typically 75W, same as 211).
Requires careful attention to filament supply — AC operation is standard for transmitting service.