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parallel 12B4s (center left) as pass elements in 585 power supply

The 12B4(A)  (P/N 154-0044-00) is a power triode tube with a B9A (Noval) miniature 9-pin base. It has 5.5 W maximum plate dissipation, 1000 V peak plate voltage, and and 105 mA peak cathode current.

The 12B4 is used in the 126, 551, and 555, and as a pass tube in the power supply of the 513, 581 and 585.

The 12B4A (154-0044-00) is similar except for the controlled heater warm-up, suitable for use in conjunction with other 600 mA types.