[Repair Hints]
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Generators and Accessories

  • RM 181 (MOD 110) Time-Mark Generator

The 181 is the “little” brother of the Type 180A Time-Mark Generator. This one I have is not a cabinet model but a rack-mount type (so RM181..). It is equipped with an temperature-stabilized crystal “crystal oven” and therefore the RM181-MOD 110 provides a marker stability of 3 parts per million (ppm) over 24 hours. I took the specs out of the catalog 24 (1965/66). The RM 181 cost about $290 that time the RM181-MOD 110 was rated at $310. You could buy the oven as an accessory for about $27.

Why do I start with a Time-Mark Generator? This instrument is the first I restored competely. First I washed the entire instrument including the electronics. Then I fixed up every failure and calibrate the instrument. After that I painted the top and the bottom aluminium covers entirely new (including a primer painting :-0  ).
top view of the RM181...
The circuitry contains the 1mc reference oscillator followed by an amplifier shaper.click to see the complete divider.. A cathode follower is “armed” by a suitable high-pass. So this is the reason for the shape of the markers. The markers are a positve impulse train. The negative impulses are “clamped” via VT diodes. If you click on the circuit you see a detail of the cascaded frequency dividers...Because of the use of a monoflop (build with V160A) the divider is very accurate to calibrate and could easily trimmed to a decade-divider. The adjustment is because of these cascaded monoflops always “stepped” with one-tenth of  monoflop time constant...
detail of the RM181..
The last pic shows a detail of the frontpanel. The serial number of the unit is 1116; it was equiped with the very out-dated UHF connectors...(I guess that we call them “PL” connector?!)

The repair hints about the RM181 will follow soon...enjoy! Please look in the Tube Testing & Repair Hints section...