41

The 41 is an indirectly heated power pentode intended for radio receiver audio output stages. Sylvania documentation particularly emphasizes car radio use, while RCA, General Electric and Tung-Sol describe operation in mains-powered or storage-battery receivers. The heater requires 6.3 V at 0.4 A, on AC or DC. The battery reference therefore also concerns heater supply: in the audio examples the plate operates at voltages far above a 6 V battery.

The sheets describe glass construction with an ST12 bulb and a six-pin base, basing 6B. Viewed from below, pins 1 and 6 supply the heater, pin 2 is the plate, pin 3 the screen grid, pin 4 the control grid and pin 5 the cathode with the suppressor grid. Any mounting position is allowed. Sylvania relates the 41 electrically to the 6K6G, and General Electric to the 6K6GT: this relationship helps explain the family, but the different bases require attention to connections and prevent direct substitution in the same socket.

RCA's 1951 sheet gives three examples for one tube in class A₁. With plate and screen at 100 V, grid at −7 V and a 12 kΩ load, it specifies 0.35 W at 11% total harmonic distortion. At 250 V on plate and screen, −18 V grid bias and a 7.6 kΩ load, output rises to 3.4 W at the same distortion; idle plate and screen currents are 32 and 5.5 mA, with 2.3 mA/V transconductance. The third example, with 315 V plate and 250 V screen, uses −21 V and 9 kΩ for 4.5 W at 15% distortion. These are circuit-specific performances with stated distortion, distinct from RCA's design-center maxima of 315 V plate voltage, 285 V screen voltage, 8.5 W plate dissipation and 2.8 W screen dissipation.

The same sheet documents two 41 tubes in class A₁ push-pull at 285 V on both plate and screen. With −25.5 V fixed bias, a 12 kΩ plate-to-plate load and a 51 V peak grid-to-grid signal, specified output is 10.5 W at 6% distortion. With cathode bias from a common 400 Ω resistor, the same load and signal give 9.8 W at 4%. These are figures for a two-tube circuit, while the 0.4 A heater current remains the value for each tube. The comparison shows that the bias method also affects output-stage behavior.

The application notes preserve useful receiver design details. The older RCA manual discourages more than one audio stage before the 41 because high amplification can cause microphonic disturbances; for a single cathode-biased output tube it calls for suitable cathode-resistor bypassing to avoid low-frequency degeneration, whereas the described push-pull arrangement does not need this bypass. RCA also recommends coupling that does not introduce excessive grid-circuit resistance. Requirements differ between documents: the older manual permits up to 1 MΩ with cathode bias under specified heater conditions, while the 1951 RCA sheet limits the circuit to 0.5 MΩ; with fixed bias the limit is 0.1 MΩ. These details call for consistent use of the data for the particular sheet and circuit.