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DF91

Sensibly equivalent to:
1F3 1T4 CV785 W17
See also:
1T4 Exploded
    
Extras ▼

 

The DF91 is a is a miniature screened pentode for dry battery operation. It was designed for broadcast radio reception and is a variable μ RF device.
This exhibit has a plan screen whereas DF91 has a perforated outer screen.
See also 1T4.
The screen obscures the inner detail but at the top the tops of the grids are visible. The grid support rods are of increasing diameter to provide the inter grid spacing.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
References: Datasheet & 1040. Type DF91 was first introduced in 1947.

 

Pin Connections
B7G
1
2
3
4
5
6
7
f-
a
g2
ic
f-
g1
f+

 

Absolute Maximum Operating Conditions
Pentode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
1.4
0.05
90
67.5
0
3.5
1.5
0.5M
0.9
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated September 25, 2019.
shape:thin.glass.tube construction:all.glass type:pentode age:1940.1950 base:b7g heater:1.4v pins:7 pin:1.f- pin:2.a pin:3.g2 pin:4.ic pin:5.f- pin:6.g1 pin:7.f+
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