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Hivac VS10G Trochotron

VS10G size The device measures 88x45mm overall and weighs about 200g. It has 26 pins on the base (B26A) arranged as an inner ring of 9 and an outer ring of 17. The outer ring has a gap as a key.

The trochotron carries the serial number 1984 and also the number 6807.

Heater voltage Vh 6.3V
Heater current Ih 0.5A
Heater to cathode voltage +/- 150V max
Spade to cathode voltage Vs 85V min, 125V max
Target to cathode voltage Vt 50V min, 300V max
Switching-grid to cathode voltage Vsg 65V max (Vs=125V)
45V max (Vs=85V)
Minimum input duration 0.5µs
Characteristics (Vs=108V, Rs=100k)
Holding spade current 1.2mA nominal
Target current 10.0mA nominal
Recommended operating conditions for counting up to 1MHz
Vs 108V
Rs 100k
(each spade must be connected to a separate load resistor with not more than 10mm of connecting lead)
Vt 108V
Rt 4.7k
(Any number of target connections may be taken to a common target resistor)
Vsg = Vs/2 54V
Vsg pulse amplitude -54V
t pulse 0.5µs
Rsg 22k
C input 330pF


VS10G insides The Trochotron is a form of counter which can operate at up to 2MHz. It is also referred to as the "beam switching tube" or "beam-X switch". It is a thermionic device surrounded by a magnet. The device has ten target electrodes arranged around the outside. An indirectly heated cathode is at the centre of the device. In between the cathode and each target is a J-shaped electrode called the "spade", and adjacent to these are flat electrodes called grids.
VS10G top mica Alternate grids are connected together to form two groups known as the "odd" and "even" grids. Each spade and target has a separate connection. The photograph shows one set of grids connected together; the other grid connections are at the base of the structure.

With the correct voltages applied, the magnetic and electric fields are such that electrons spiral around the cathode in a trochoidal curve - thus the name Trochotron. With all the electrodes positive the beam is not attracted to any of them due to the uniform radial electric field created. When a spade voltage is lowered to ground, it distorts the field, allowing electrons to strike the associated target, and the beam locks in this position. The beam is moved around the targets by applying a negative pulse to the 'even' and then 'odd' grids, bumping the beam round each time.

Pin Function Pin Function
1 Spade 0 14 Spade 2
2 Target 9 15 Target 1
3 Target 8 16 Even switching grids
4 Odd switching grids 17 Target 0
5 Target 7 19 Spade 9
6 Spade 7 20 Spade 8
7 Target 6 21 Heater
8 Target 5 22 Spade 6
9 Spade 5 23 Spade 4
10 Target 4 24 Spade 3
11 Do not connect 25 Heater
12 Target 3 26 Spade 1
13 Target 2 27 Cathode

See also ET51, 6700 and BX1000.


Warning label

Part number

Inside view!
Here is a dismantled one, without the magnet!

VS10G getters


Bottom quarterTop quarter


This file was last modified 15:19:16, Tuesday September 02, 2014