Well, I have had a bit of a look at the posted schematic for the EE as part of the thyratron replacement project.
The circuit is fairly simple, although some of the interactions among the parts are the complex part. Also, the factory settings are dependent on tube characteristics, so as tubes age, the proper seting of the limits and the compensation will change. When new tubes were easily obtained this was not a problem, but now it will be necessary to re-setup some units. And, of course if someone has tried to re-set them without instructions, they may need it too.
That page is missing from the posted material, I asked Art to try to get the page(s) preceding the page posted as "Elect-3.gif" which should have that info.
On the posted unit:
The armature control is by phase-controlling the two C16J thyratrons. They get alternate half-cycles of the AC input through a transformer, and output full-wave rectified DC to the armature.
The voltage is changed by controlling how much of a half-cycle is let through, a longer delay before firing lets through less energy, and so lowers the voltage. An AC signal in synch with the line is provided as a firing voltage, which if uncontrolled would send it to max voltage by immediately firing the tube on each half cycle.
The speed control directly varies the delay (phase angle) in a manner similar to the way a household lamp dimmer works. The 6H6 and the 6N7 tubes control this by varying a DC bias on the thyratron grids.
The AC firing voltage in synch with the incoming line comes from the transformer connected to 73 and A25 on the schematic. Firing signal is thus the sum of the DC bias and the AC firing voltage, so if the bias is reduced, firing is later and produces a lower voltage.
The bias is partly dependent on the armature voltage. A feedback through the "max voltage" control acts to loosen the bias and raise the armature voltage if it drops, or clamp the bias down and reduce voltage if it rises.
The kicker is that there is also a current sense transformer. This varies the effective control voltage (via the compensation control) with current. The 6X5 tube is for this purpose. More current draw raises the armature voltage, by partly shutting off the 6N7 tube.
This will prevent slow-down under load as the back EMF of the armature drops off with the lower loaded-down speed. That would otherwise reduce armature voltage by reducing the load impedance.
The shunt field has no special current feedback control, it is a simpler lighter duty version of the armature controller, using the lower power 3C23 thyratrons and the 6SF5. It presumably acts as the field weakener.
The speed control is a dual type with probably a "dead zone" on each half where only one of the two elements varies as you turn it. This allows the upper range to be controlled by field weakening only, with the armature probably held constant. Correspondingly, in the rest of the range, the field is presumably constant, and only the armature current varied.
With regard to replacements, several tubes are easily replaced with solid state parts, although the SS parts might have to be wired onto tube-base type plugs to be directly installed without fuss.
The 6H6, the 6X5 and the EL1C are rectifiers/diodes, and can be replaced with solid state rectifiers directly. The circuit does not appear to depend strongly on their characteristics, because of the large resistances associated with them (tube voltage drop is less important at low current / high impedance).
The 6NO60 should be a 6 volt heater time delay relay, with NO contacts, and a 60 sec delay time. I don't know about direct replacement availability of these.
It is used to let the thyratron and other tube heaters warm up (2.5V @ 31 ampere heaters for each C16J!). You can't use the start button until this relay closes, because its contacts are in series with the start button contact.
Time delay relays (solid state) are available new these days, maybe with compatible basing (not certain of that), and should be adaptable one way or another.
I would NOT recommend bypassing the TD except in an emergency because it may lessen tube life if you draw current before complete tube warm-up *. If you do have to kludge it, count off the minute before starting up.
For the 6N7 and the 6SF5, you are stuck for the moment, as they are amplifier tubes, and are used in the servo system. Characteristics are important to maintain speed.
* The thyratrons are gas discharge tubes, not arc type tubes. Thus their emmission is dependent on the capacity of the heater cathodes. If too much current is drawn, or the tube not warmed up first, the emission material may be damaged permanently.
A mercury arc tube, such as an ignitron in a welder, has a huge overload capacity by comparison. But their drive needs are quite a bit heavier, many amps of trigger current, not just a voltage as with thyratrons.
[This message has been edited by J Tiers (edited 04-05-2002).]
