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The O-12 5MHz bandwidth oscilloscope came on the market in 1958. The O-12 is practically the same as the O-11 that came on the market in 1957. It has lots of similarities with all previous Heathkit oscilloscopes and can, more or less, be traced back to the very first O-1, that was the first Heath kit back in 1947. The O-12 was replaced by the IO-12 and IO-12U* in 1962, which in turn was replaced by the IO-18 and IO-18U* in 1968 and they were replaced by the IO-102 in 1971. (See also the IO-104 page).
*The Brittish Heathkit factory in Gloucester produced several kits with the letter U added to the designation. Among them was the IO-12U and the IO-18U. The U meant The United Kingdom. The IO-18U differed from the IO-18 in terms of a slightly modernized style like the rectangular CRT.
My oscilloscope is marked as the O-12E model. The E stands for Export and means that it is meant for 115/230V supply voltage. I bought this oscilloscope in the mid 70's together with the probes and the electronic switch ID-22 that makes the scope dual channel. And they are all still in working condition. I added a BNC input connector and colorized the tops of the knobs in a logic manner to enhance the usability. I separated the chassis from mains ground and instead connected it to a terminal on the front panel.
The schematic of the original unmodified O-12
Even if it says "Laboratory Oscilloscope" on the dashboard, the O-12 has, as well as its predecessors (O-9, O-11, etc) and its successors (IO-12, IO-18, IO-102, etc) quite limited use, since both its vertical gain and horizontal sweep is uncalibrated. Only relative messurements can be made. And only AC messurements can be made due to the simple input stage.
I have modified my O-12 to make it quite more useful. I have made a new CRT graticule with 1cm grid. The input stage is calibrated with '1' - '3' intervals and the switch is replaced with a 6 step 2 gang type and the range is from 10V/cm to 30mV/cm.
Also the sweep is calibrated with '1' - '3' intervals and the switch is replaced with an 11 step type that result in a range from 10ms/cm to 1µs/cm. The sweep is not perfectly linear, thougt. A sine wave is somewhat expanded in the beginning and slightly compressed in the end.
The schematic of the modified O-12