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ORA

 
See also:
Mullard R & ORA Advert - Mullard ORA Advert - Mullard ORA Advert - Mullard ORA Advert - Mullard ORA Advert - Which Valve Shall I Buy?
    
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The ORA from Mullard was designed in 1922 as a development of the K valve and the redesign was prompted by the commencement of broadcasting. This valve is either an early ORA or a K valve.
This exhibit has a helical grid welded to a support rod and not held in twisted wire supports like ORA.
It is possible that this valve could be a K but there is no indication on the envelope. Also it is possible that this exhibit shows how expensive hand made bright emitter valves were in the early 1920's as it has been repaired. The only identification on the glass is that it was 'Repaired by Crowther and Osborne Ltd'.
The anode is 10 mm long and 10 mm in diameter. The grid has 11 turns.
The plating on the base shell has worn off leaving the copper exposed. The pins are a of a simple split pin construction.
Looking down into the anode. The majority of the filament remains attached to the lower support and has broken just below the helical at the top. Note also the support rod on the right that has been welded back together.
The top of the filament showing the helical twist and the break.
Here the break in the filament is on the left. The lower turns of the grid are discoloured due to heat.
The base shell infill looks to be made of wood and has shrunk over time. The envelope, base and skirt are all loose.
The thin glass tube envelope is 28.6 mm in diameter, and excluding the B4 base pins, is 92 mm tall.
References: 1003 & 1004 Type ORA was first introduced in 1922.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
ra
gm
3.8
0.65
30-90
27,000
0.32
Updated May 20, 2015.
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