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 the introduction of the 6.3 Volt heater in 1935. When fitted with a 6.3 Volt heater the Type 55 becomes a Type 85.

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.

 
Pin Connections

UX6	1	2	3	4	5	6	tc
	h	a	a(d2)	a(d1)	k	h	g1

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vg	mAa
	2.5	1.0	250	-20	8.0

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 10 March 2008 {find valves by name}