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    - I (Ed Thelen) was on an Ajax site 4/55-1/57
    - A.J.M.Weijenberg was on a Hercules site 1/69-6/72

Table of Contents
     - (Vacuum) Tube Tester
     - Volt Ohm Meter
     - Synchro Scope
     - Wheatstone Bridge
     - more ;-)) Dec 29, 2014

(Vacuum) Tube Tester
A.J.M. (Jos) Weijenberg sent these pictures to remind me of "the good old days" ;-))
Tube Shop

Also often in a drug store

Tube Tester

Near by was a multipage chart showing switch setting for each of several hundred tube types it could test
We in the IFC had a tube tester similar to this (A.J.M.Weijenberg thinks there was no tube tester in the launcher area. )

When part of a system didn't work, and the interlock switches were either correct or cheated, a good plan was to try to locate the failing circuit by dividing the signal chain in half, then in half again, ... using various operational tests, switches, oscilloscope, ... whatever it took.

When a circuit in a chassis didn't work correctly, (and all the filaments were lit ;-) a person had several options.

  1. (We did not have spare chassis to swap)
  2. In general we had spare tubes. Then "Easter Egg" it - swap tubes until the circuit worked or determined the fault was not a tube
  3. If the tubes seemed good, maybe a "passive" component (resistor, capacitor, diode, rarely a transformer) was at fault. If it wasn't something obvious - broken wire, smoked resistor, ... then you needed a scope and circuit knowledge. Fortunately, our training was very complete, and we were young with retentive memories :-))
  4. We were not equiped with many passive components - the chassis could go back to Ordnance for swap and repair. Fortunately this was very rare - other than the lump in the TTR elevation potentiomenter which we discovered, I think the only chassis we had to swap out (down time) was due to smoked resistors in the pulse code generator in the MTR.

Volt Ohm Meter
We had a good rugged analog meter similar to this. (Digital meters for field use were not available yet.) It was in a leather case and could stand up to normal field use.

Synchro Scope
We also had an oscilloscope which was a ruggedized simplified version of the nice Tektronix oscilloscopes we had in the school labs. The sync circuit for the sweep was simply a coax to the 1000 Hz ( 400 Hz in the Hercules) "clock" that drove the magnetrons and most of the display scopes in the IFC. Although it did its intended job well, I really disliked it 'cause you couldn't play with it, like display voice wave forms because the sweep trigger circuit was so primitive :-((

If you look up "Synchroscope" now, you will find a display used to help synchronize two AC generators - not our equipment at all.

Wheatstone Bridge
Wheatstone bridge from Wikipedia.

Ours was a brief case size instrument in a polished plastic case, intended for gentle handling. Before moving it you wanted to slide a little "button" to clamp the sensitive galvanometer movement so that the little pivots or fine wires wouldn't break.

This Wheatstone Bridge was used to check voltages under test condition in the analog computer.

Dave Lion has a Wheatstone Bridge with an external galvanometer here. Wikipedia mentions galvanometers with 100 micro amps full scale, ours had about 20 divisions so possibly we had 5 microamps per division. And of course you could balance to well under one division, lets say one tenth of a division.

more ;-))
from A.J.M.Weijenberg, Dec 29, 2014
Some comments on your additions (based on my memory of the situation around 1970 on a Dutch site in Germany).

Tube tester. I do not think they had a tube tester at the LA. Most equipment besides the missile itself, over there was just ‘switching’ equipment. So a simple PSM-6 would be needed to troubleshoot most of the equipment. Although I was not an LA specialist, it would not surprise me if there were no tubes used at all in the launching equipment. Maybe in the intercom amplifiers near the launchers?

The missiles, including the missile simulator, used mini tubes. The testing was done using test points at the card or module edges. Come to think that maybe tubes were used in the missile test equipment. But I do not think they troubleshot test equipment on the LA.

Multimeter. We used extensively the AN/PSM-6 ruggedized multimeter on the IFC. I have attached a picture of this multimeter.

Bridge of Wheatstone (BoW). I do not recall that we used a BoW to measure voltages in the computer. As far as I know, normally voltages are not measured with a BoW. However it makes sense that we precisely measured voltages for testing and troubleshooting the computer. Maybe the black box that I remember as a BoW was another type of tester! It had however a galvanometer with a slide you had to unlock before using the meter and also a bunch of decade switches.

Synchro scope. I do not remember this.

RF-test set. Antenna to aid in the optical/electrical/mechanical alignment of the tracking antennae. (I forgot how the TRR was aligned.)

Missile simulator. Located at the LA in a mast on the Launching control Van. It simulated the Missile electronics and the MTR could lock on to it. Inside the van you could read the steering information sent by the MTR.

Spares. On our sites we had not only all kind of spare tubes but also spare chassis/modules. For sure we had power supplies, RF amplifiers and computer amplifiers (you remember the rattling of the zero switches?). We also had spare magnetrons and lighthouse tubes. We had also all kind of spare lightbulbs, fuses, relays and switches.

(Built in) test equipment.

The IFC equipment had quite a lot of built in test equipment/functions. Some that I remember

X channel event recorder. (recorder that used light beams reflected by galvanometers with tiny mirrors to expose photo sensitive paper rolls). After recording you had to develop the photographic paper rolls before you could analyze the recording. For developing you used an apparatus with several chemical baths. The recorder was, besides having the intention to record live and simulated firings, used for computer testing (sim track) or troubleshooting.

MTI-scope. Scope to check the Moving Target Indicator system (delay line) in the LOPAR.

Zero pips. Function to set or calibrate the MTR range zero point. (Forgot how this worked!)

TRR oscilloscope. Used for monitoring TRR signals. This was a normal double trace oscilloscope that came in handy for using general troubleshooting the system in place of the ‘normal’ single trace scope.

The most advanced test equipment I remember was a peace of plastic with a ½ or 1 inch marking to check the level (hight) of the noise? or the returned target signal? on the az/el/range scopes of the tracking antennae ;-) consoles in the RC van.

Hope you remember some too and maybe add to this overview.

BTW During the hands-on training at Fort Bliss to troubleshoot the system it was common to check if the filaments of the tubes were lit (eyeballing not allowed!!). In real life this was almost never the cause of a problem ;-)


Jos Weijenberg