HP 122A Oscilloscope Service Manual

The last evolution of the oscilloscope product line before the end of the 50's, the 122A was introduced in the September 1958 Hewlett Packard Journal under the title:"A Dual-Trace Automatic Base Line Oscilloscope For the DC - Several Hundred KC Range"
It is a dual-channel version of the 130A which permits two separate waveforms to be viewed simultaneously. To permit an optimum display for a given application, two modes of dual-trace display are available. For the lowest frequency signals the CHOPPED mode will switch electronically between the two vertical amplifiers at a 40 kc rate. For higher-frequency signals the ALTERNATE mode will be preferred to avoid the risk of any harmonic relation between the observed signal and the 40 kc chopping frequency.
To insure stability of the low-level vertical amplifiers, the vacuum tube heaters are voltage regulated. Transistors are used as the control elements in the heater regulator. This makes the 122A one of the very first instruments to integrate transistors in its circuitry.

Interior Panoramic View of the HP 122A