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This exhibit was made by M-OV at Hamersmith and was for many years at Brunel University. The closest we can come to the actual Type of this valve is the EHT1 but this looks to be an experimental variant.
From the Saga of the Marconi-Osram Valve comes the following two paragraphs relating to the EHT1 EHT rectifier.
CV19 (EHT1): was the military version of the EHT1 high voltage rectifier used, in this case, in the MB2 radar. One of its main identifying feature was the torpedo shaped bulb designed to occupy a minimum of space. The EHT1/ CV19 used a simple anode but special baffle to limit spurious emission. The filament was shaped almost spherical and joined at one end in a knot.
This unusual valve rectifier had been designed at M-OV in the pre-war period and was the first of the extra high voltage, high impedance rectifiers and triodes. It was used in the Cockroft electrostatic generators of super-high voltage, in this case with a hold-off voltage of 80kV though some related valves would work up to 250kV. It could be used in half-wave or full-wave circuits, in the latter case with a mean current of 132mA, or in voltage doubler circuits. The device used a bright emitter directly heated, tungsten filament with 17 Volt, 10 Amp rating. The user was advised to run the device up slowly and carefully in the first instance with a high resistance in the circuit, 0.1-1 megohms, in order to condition the device. He was also advised to screen the valves against X-radiation. The valve was used in cable testing and dust precipitation and other applications such as X-ray machines.
The special base cap and Ediswan Screw are on the left with the anode on the right. Most of the lettering this side has rubbed off.
The simple bright cylinder anode. Note the absence of the baffles referred to in the reference quoted above.
This enhanced image shows the Word Type and then a space to the 3 and what looks to be a C or G. A number appears below - 661 and is probably a serial number. This valve was donated by Terry Purser and he believes that the original lettering after the word Type was 613C. We can find no information on a Type 613C rectifier.
Here the filament can be seen. From each support are two filament strands and each is held at the centre by its own separate support. The effect is to generate a spherical effect. Clearly no other baffles etc. are present.
The balloon envelope is 128 mm in diameter, and including the ES base is 540 mm tall.
References: Datasheet & 1005.


Absolute Maximum Operating Conditions
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated June 28, 2014.
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