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Readouts and Counters

(Continued from page 591

electron stream thus rcvolvos likc the spoke of a wheel. remaining in each of the ten positions used until the next in-put pulse is applied. After ten input pulses, the electron stream is back to the initial anodę target. and an output pulse. as is usual for such decadc counters, is produced at that point.

A morę complete understanding of this action is possihle with the help of Fig. 9. This shows that two other elec-trodes are associatcd with each target. The one identified as the spade is used to "lock" the electron stream in its path to one anodę until the next input pulse is applied. The other electrode. known as the switching grid, is used to transfer the electron stream to the next target. The not unexpected sequonce from 0 to 9 identifies the individual targets in the sequcnce.

Although it is not shown in Fig. 9. all even-numbered switching grids arc tied together internally. rcducing the number of base pins rcquired and sim-plifying Circuit wiring. For the same reasons, the odd-numbered switching grids arc also connected internally. Al-ternatc triggering of the odd and ovon grids will deflect the electron stream so that it transfers from target to target in sequencc.

A Circuit designed around the MBS tubę is shown in Fig. 11. The tubę it-self appears in Fig. 10. In the Circuit shown. a binary stage is used to trigger the switching grids. The back-and-forth action of two triodes in the binary provides the alternate switching required. Cathode-follower cou-pling is used to reduce the loading effect on the binary Circuit.

As ever. there must be some way of clearing the tubę and re-setting to the 0 target. In the technique used. a posi-tive pulse applied to the common cath-ode cuts off the electron stream alto-gether, thus providing clearing. The pulse is applied at the point marked "pin D, elear" in Fig. 11. A negative pulse is simultaneously applied to the Circuit, fceding to spade 9 at the point marked "pin H, re-set." This causes the beam to form in the 9 position, where it is ready to be transferred to the initial or 0 position.

A check of the Circuit will show that the negative re-set pulse is also applied to the binary stage used for switching. Action of the binary then advances the heam to position 0, the desired start-ing point.

The MBS tubę is identified as a type BD300 or BD301. A 5963 is used as the binary. The two sections of the 12AU7 act as the cathode followers, one for each sidc of the binary. For simplicity. only some of the targets with their associatcd electrodes appear in Fig. 11. Target 1 shows the types of Circuit conncctions for all odd-numbered an-odes: target 8 shows as much for oven-numbered anodes; while targets 0 and 9 show the special conncctions required for clearing and re-setting the Circuit to zero.

Another, important item in the schematic has not bcen mentioned. This tubę. the 6844A, is a Nixic indi-cator. Obviously then, the MBS and the glow-transfer tubes differ in another important respect: the former is not self-indicating. However, where the greater counting speed it makes possiblc is desired. one factor balances out another.

It would obviously be impossible to cover every Circuit and every type of indication used in electronic counting. However. the leader of this and pre-ccding articles in this scries has had the opportunity to become familiar with circuits and special components that cover the vast majority of actual applications. A fortheoming article will cover counting and coding systems ac-tually used.

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