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7D8

Sensibly equivalent to:
ARP9 CV889 CV1327 Pen1340 Pen13C
See also:
Brimar 15D1, 9D2, 11D3, 10D1, 4D1, 7D3, 7D6, 7D8, 7A3, R2 & 1D5 Advert
    
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The 7D8 is an audio output pentode from the mid 1930's. It has a 13 Volt heater at 0.65 Amps, neither clearly for parallel or series heater chains. The advert cites motor car sets as a use - this would make sense of the 13.0 Volt heater.
The 7D8 should operate with 8,500 Ω load and a 150 Ω cathode resistor. Under these conditions the audio output is 3.75 Watts.
The Brimar orange/yellow paint and the pinch.
The cathode is seen as a broad flat box. The inner grids pass flat across the cathode.
An enhanced view of the grids.
The classic envelope is 39 mm in diameter, and excluding the B7 base pins is 99 mm tall.
References: Datasheet, 1040 & 1043. Type 7D8 was first introduced in 1935.

 

Pin Connections
B7
1
2
3
4
5
6
7
-
g3
g2
h
h
k
a

 

Absolute Maximum Operating Conditions
Pentode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
μ
13.0
0.65
250
250
-6
32.0
6.0
60,000
10.0
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated March 19, 2014.
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