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6AK8

Sensibly equivalent to:
6LD12 6T8 DH719 EABC80
    
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The 6AK8 has three separate electrode sections within the envelope. The triode and two diodes share a common cathode and one diode has a separate cathode.
The 6AK8 was specifically designed for use in the detector stage of early FM and FM/AM radios. The triode section providing the first audio amplification, one half of the double diode for AM detection and the single diode and one of the diode pair for FM demodulation, probably in a ratio detector circuit.
It should be noted that the operating conditions for this Cossor valve differ from the sensibly equivalent EABC80 from Mullard.
Seen at an angle to the broad face of the anode the slender box construction of the electrode assemblies is revealed. The strips on the left are the heater supply connections and the pair spread to the outer heater connections. The returns from the outer sections are then connected to the middle section via strips fixed to the top mica, thus putting all three sections in series.
The triode section is on the right, the single diode is on the left and the middle box is in fact two L section anodes that forms the double diode.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins, is 58 mm tall.
References: Datasheet, 3002 & 1040. Type 6AK8 was first introduced in 1952.

 

Pin Connections
B9A
1
2
3
4
5
6
7
8
9
a(d3)
a(d2)
k(d2),s
h
h
a(d1)
k
g1
a

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
6.3
0.45
100
-1
0.8
54,000
1.45
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated May 22, 2014.
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