While the type 884 thyratron is certainly comparable to the type 6Q5G in many respects they are not interchangeable, which is why equivalents lists are never totally accurate.

For a start, type 6Q5G is normally fitted with a 5-pin (USS5) base cap (as type 885/CV648) rather than IO (as type 884/CV647). Reference sources also show some differences in data and in intended usage, the 6Q5G being rated for sweep generation and grid-controlled rectification whereas types 884/CV647 and 885/CV648 are both classed as 'relay tubes'. Possibly the types have different specifications for gas filling. This can make a big difference to performance. We believe that this difference became clear to the Colossus rebuild team.

The classic envelope is 36 mm in diameter, and excluding the IO base pins, is 86 mm tall.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a	-	g1	-	h	k

 
Absolute Maximum Operating Conditions

Thyratron	Vh	Ah	Va	mAa
	6.3	0.6	300	300

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 12 June 2007 {find valves by name}