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P425

 
See also:
BSA Standard P425 Box - Valves
    
Extras ▼

 

BSA Standard sold STC valves during 1926. The P425 is a battery output triode and some operating details are printed on the box. What is not given is the output power.
Through a gap in the gettering the electrodes can be seen. The anode is a flattened cylinder with two side plates holding it. The side plates pass down to a collar around the pinch stem. The collar has small crimps around the circumference that probably allow some 'give' to enable the collar to be a tight push fit onto the cylindrical pinch stem.
The anode retaining collar is just visible on the left. The anode is a flattened cylinder and the control grid has rounded edges that match the anode. The filament is a single inverted V that is held in tension by the spring fixed into the glass bead at the top.
Here the anode support plates can be seen to have turned-up edges that add considerably to the stiffness of the structure. The helical spring has a hook at the lower end to hold the thoriated tungsten filament.
This image shows the filament and the tension spring more clearly.
The data-sheet packaged with the valve
The balloon envelope is 59 mm in diameter, and excluding the B4 base pins is 100 mm tall.
Reference: 1043. Type P425 was first introduced in 1926. See also 1926 adverts.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
μ
4.0
0.28
130
-2.0
25.0
6,000
1.1
6.6
Updated March 22, 2022.
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