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4215A

Sensibly equivalent to:
H125 Wecovalve
    
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In the UK Western Electric valves were made by STC and given the initial digit 4 and thus this is a STC made valve.
The filament is given as 0.8 to 1.1 Volts at 0.25 Amps. The anode voltage was quoted as 15 to 30 Volts for the orange spot, and 30 to 60 Volts for the other two types. The red spot was designed to operate with a grid bias of -3 to -5 volts and used as an RF amplifier. The green spot was designed as a detector with the grid at -7 to -10 volts. Finally the orange spot type was specified as an audio amplifier and to be biased to -3 to -5 volts. All three types were introduced in 1925, had an ra of 25K Ohms, a mutual conductance of 0.22 mA/V and an amplification factor (μ) of 5.5. However, this example has no obvious colour spot - at first sight. Looking more closely there is a small and faded orange spot near the base. This can be seen in the image above just above the locating pip for the bayonet base.
The Wecovalve name and patents for 1915 and 1921.
The top of the cylindrical anode shows the quite thick grid wire that is formed as a helix. The filament tension spring and single strand filament is also visible.
The top view of the Peanut base. The base connections are marked on the bakelite.
Side view showing the slot for the locating pin. The base is 38 mm in diameter and 20 mm from bottom to top.
The underside of the base. The connectors are sprung to ensure good contact.
The valve complete with Peanut base. The orange spot is easy to see when you know it is there.
The thin glass tube envelope is 15 mm in diameter and, including the Peanut base pins, is 63 mm tall.
References: 1003 & datasheet Type 4215A was first introduced in 1923.

 

Pin Connections
Peanut
1
2
3
4
g1
f
f
a

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
μ
1.0
0.25
30
-3
1.0
25,000
6
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated September 28, 2017.
shape:thin.glass.tube construction:pinch type:triode age:1920.1930 base:peanut pins:4 pin:1.g1 pin:2.f pin:3.f pin:4.a
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