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DFA1

 
See also:
DFA1 Box - Mullard DFA1 & DFA2 Advert - Mullard DFA0, DFA1, DFA2 & DF.ORA Advert - Mullard DFA Advert - The Dawn of Broadcasting in the UK
    
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The DFA range of triodes was designed for the output stages of broadcast receivers. The box describes the DFA1 as for power amplification to drive the largest loudspeakers. In 1924 when the DFA1 was issued the speaker would have been of the moving iron or reed type and probably fitted with a horn.
The paper label on the nickel base shell describes the warranty conditions and then gives the filament and anode ratings.
The envelope carries the third style of BBC stamp that dates this exhibit to between September 1924 and 1927. With the metal base shell this valve is most likely from 1924 or 1925. The base has the Mullard name embossed on it.
The Mullard logo with DFA1 and the words Registered Trade Mark.
The balloon envelope is 53 mm in diameter, and excluding the B4 base pins is 99 mm tall.
References: 1003 & 1043. Type DFA1 was first introduced in 1924.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
μ
5.5
0.23
50-100
-4.5
-
5,500
1.0
5.5
Updated September 06, 2019.
shape:balloon construction:pinch type:triode age:1920.1930 base:b4 heater:6.0v pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f
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