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NU7

Sensibly equivalent to:
CV1262 GU1
    
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The NU7 is an interesting rectifier as the mercury can be clearly seen on the inside of the envelope. The heater is a thick coil of ribbon and the anode is a curved plate.
The civilian prototype of the NU7 is the M-OV Type GU1, introduced in the mid 1930s. The GU1 was very popular as a rectifier for cinema amplifiers (etc) but it had a short life and was discontinued in favour of the GU50.
See also GU1.
The four turn helical ribbon filament has an additional support in the centre that is not electrically connected.
The centre filament support is partly covered by ceramic.
The small cylinder with flattened ends looks to be sealed but may have been the original mercury container.
The balloon envelope is 45 mm in diameter and excluding, the B4 base pins, is 93 mm tall.
References: Data-sheet. Type NU7 was first introduced in 1930.

 

Pin Connections
B4
1
2
3
4
a
-
f
f

 

Absolute Maximum Operating Conditions
Rectifier
Vh
Ah
Va
mAa
4.0
3.0
1000
250
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated June 14, 2021.
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