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SP-18 Green

 
See also:
The Dawn of Broadcasting in the UK - Shortpath Construction
    
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The SP-18 Green spot was introduced by Cosmos in 1925 as a general purpose valve alongside the SP-18 Red AF and Sp-18 Blue for Resistance/Capacitance coupled circuits.
Here we have the Cosmos short path valve branded as from Benjamin Electric. Benjamin made excellent valve holders but were not manufacturers of valves.
The reverse of the envelope. The silver coating inside the envelope obscures most features.
The top of the anode. The grid is just visible and above the electrodes a glass bead holds the supports firmly.
Another view of the top looking down on the anode. The grid support is on the right and the filament top connection is on the left.
The pins have a single split and the contact with the lead out wires is made at the top outside the plastic base.
The anode can be seen to be long in relation to width and depth.
The valve came with a two sided printed sheet. This graph is from this data sheet.
The thin glass tube envelope is 25 mm in diameter, and excluding the B4 base pins is 98 mm tall.
References: Datasheet & 1043. Type SP-18 Green was first introduced in 1925.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
μ
1.8
0.3
120
-6.0
-
17,000
0.88
15
PDF scanned from an original document held by the museum
Updated February 23, 2013.
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