Sensibly equivalent¶ to:
The Type 55 is a double diode triode designed for use as signal and AGC detection and first audio voltage amplifier in domestic broadcast receivers. The 2.5 Volt heater was the American initial standard for indirectly heated valves prior to adopting the 6.3 Volt heater as standard. When fitted with a 6.3 Volt heater the Type 55 becomes a Type 85 that itself becomes a Type 6V7G when fitted with an IO base.
The internal pattern is typical. A common cathode passes through a bright box which is the pair of diodes and then on through the triode section. On the extreme left of the picture one can see the grid connection passing to the top cap.
The paper band around the top of the envelope is printed with the words - quality approved - special export test.
The classic envelope is 38 mm in diameter, and excluding the UX6 base pins is 100 mm tall.
References: Datasheet, 1040 & 1043. Type 55 was first introduced in 1936.
Absolute Maximum Operating Conditions¶
Updated February 15, 2013.