I'm trying to understand this paper. It describes a counter using a ring of thyratrons.
I don't understand what the capacitors Cp, Cq, … , Ct do. It looks like the circuit would work without them.
I also don't understand why the batteries Bq, Br, … are there. They're connected the opposite way to the H.T. battery, so it looks like they just reduce the bias that a thyratron provides to the next thyratron. Could the voltage of the H.T. battery be reduced and the other batteries be removed?
The capacitors couple the trigger source to the grids of the thyratrons. Without the capacitors they would not sense the trigger signal or count it.
The trigger signal is expected to be a pulse that overcomes the negative bias provided by the batteries to cause the thyratron with the most positive grid to go into conduction.
When a thyratron conducts it creates a pulse from the cathode that is coupled to all other thyratrons by capacitors Kx causing the previously conducting one to cease conduction.
Between trigger pulses the single conducting thyratron raises the grid bias of the following device by coupling via the battery from the cathode. This makes it more sensitive to the trigger pulse so that it is the only one that triggers next time. This way the conducting device moves around the ring as pulses are received. The capacitative coupling to the grids allows each device grid to have a different DC voltage and so control whether it is triggered by the incoming pulse or not.
The counting meter driver X is biased from the grid bias of device P so it will trigger every five pulses. There is a contact driven from the meter armature so the thyratron and the coil are turned off as soon as the meter is triggered. When the counter armature returns to the rest position the thyratron will be in the non-conducting state ready for the next operation five pulses later.
The C caps trigger one Thyratron to latch at a time and then reduces the negative bias of the next stage in a daisy chain ring like ENABLE D in a flip-flop. The K caps act like relay contacts except injecting an opposing cathode voltage to quench the arc below its latched holding current threshold, like RESET for the next flipflop.
The gates have a large negative bias to inhibit false triggering and when critically biased only one Thyratron can trigger an arc at a time.
So it acts like a ring shift register and was slow enough to work on early dial-pulse telephone counter selectors yet fast enough to count alpha particles. It sounds clumbsy with the critical gate biasing , step voltage and RC time constants required to prepare each next stage for triggering but it worked.
This PhD student's research combined the results of others but eliminated the relay reset feature, so there were no moving air-exposed parts (except burning electrons in vacuum tubes and the actuator counter))
By C. E. Wynn-Williams , Ph.D., Exhibition of 1851 Senior Student. (Communicated by Lord Rutherford, F.R.S.—Received March 31, 1931— Revised May 9, 1931.)
The capacitors \$C_{P}...C_{X}\$ couple the pulse from the transformer to all the thyratron grids at the same time. The capacitors are needed to provide grid bias isolation. The transformer would pull all the grids to zero without them. As well, one of the grids is just below trigger level while all others are biased negatively relative to the cathode. The trigger pulse can then overcome the bias voltage of only one thyratron at a time.
In the circuit diagram, the arrows next to thyratron Q indicate that Q is conducting with a current \$I_{Q}\$. All others are off. Thyratrons cannot turn off until the anode-cathode current drops to zero. I will talk about tuning it off later.
Look at the grid voltages for all the thyratrons except R. The grid voltage is set by the battery plus the voltage \$V_{pot}\$ across the lower half of the cathode potentiometer of the previous stage. Since the previous stages are not conducting, \$V_{pot} = 0\$. So the grid voltage is set by the negative voltage supplied by the battery. So when the pulse arrives on the grid it cannot overcome the grid voltage so the thyratrons stay off.
Look at the grid voltage for R. Because there is current \$I_{Q}\$. \$V_{pot} > 0\$ raising the grid voltage sufficiently to allow the pulse to overcome the grid bias thereby turning on R. The sharp rise in \$I_{R}\$ drives R's cathode voltage up. This voltage is coupled by capacitor \$K_{QR}\$ to Q's cathode driving it high enough to turn Q off.
Every pulse then causes each thyratron to turn on in sequence. Thyratron X gets turned off immediately by the counter relay.
