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DE5B

Sensibly equivalent to:
CV2892
See also:
The Dawn of Broadcasting in the UK
    
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The DE5B is a dull emitter triode designed to be used as a resistance-capacitance coupled audio amplifier. The amplification factor of 30 and the high impedance all suggest that this valve was designed as a driver for the DE5A output valve.
The DE5B was the final valve in the family with DE5 and DE5A as well. This valve is half silvered showing that the valve was magnesium gettered and this is typical of all three.
The following is an extract from Barry Vyse's Saga of the Marconi Osram Valve1005.
'....DE2, DE3, DE4, DE5, DE5a, DE5b, DE6, DE8, DEH6l2 and DEL612, these were all general purpose, amplifier triodes incorporating the new thoriated tungsten filament cathodes. In addition, in the DE4, DE5 with its variants and DE8, the valve construction was of a more advanced design. The electrode structure had been flattened so that the valve worked more like a two sided, parallel plate triode than a cylindrical triode. The idea was undoubtedly to accommodate the much larger filament and to improve the mutual conductance. One might say that an optimum compromise had been found between the early extremes of the flat plate audion structure and the cylindrical design of the R-type. The molybdenum grid was wound on nickel posts and the cathode constructed in the shape of a V or an M. The nickel anode had indentations impressed to add rigidity and the whole electrode structure was built up on stout nickel pins held in-line by the glass pinch. The advanced nature of the design is revealed by one further change - there was no visible seal-off pip on the later versions - another innovation derived from the lamp works. The designers had learned how to incorporate the pump stem into the pinch. All in all, with the pear shaped bulb and bakelite cap, this range of DE valves emerged looking quite modern'.
The base and pin construction. The pins are made in two parts and the flared top to the lower element would make a tight fit to the socket. The connecting wire is soldered to the outside at the top nearest the Bakelite base. The centre of the plastic base has M O V Co LTD moulded into it.
The grid and single inverted filament. At the top left the etched dome lettering can be seen.
The filament tension spring. On the glass can be seen the etched lettering with the DE5B feintly visible.
The balloon envelope is 56 mm in diameter, and excluding the B4 base pins, is 93 mm tall.
References: 4051, 1005 & 1003 Type DE5B 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
5.0
0.25
120
-2.0
5.4
30,000
0.67
20
PDF scanned from an original document held by the museum
Updated March 29, 2013.
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