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WD709

Sensibly equivalent to:
6N8 EBF80 ZD152
See also:
Valves and their Habits
    
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The WD709 is a variable μ amplifier pentode and a pair of signal diodes in the one envelope. Probably this was designed as was the later EBF89 as final IF amplifier and AM detector. The other diode would provide AGC rectification.
Here is another example of this valve from Marconi. In this exhibit the glass foot and envelope are fused to leave a groove. The UK manufactured valves have a rounded base after the two types of glass have been fused together. I believe this groove construction indicates a Philips factory.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 56 mm tall.
References: Datasheet & 1040. Type WD709 was first introduced in 1950.

 

Pin Connections
B9A
1
2
3
4
5
6
7
8
9
g2
g1
k,s
h
h
a
a(d1)
a(d2)
g3

 

Absolute Maximum Operating Conditions
Pentode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
6.3
0.3
250
85
-2
5.0
1.75
1.4M
2.2
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated September 12, 2013.
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