This is an oscilloscope trace doubler, based on a design appearing in Electronics Australia Magazine Feb 1981.
LINK TO TRACE DOUBLER Cct from magazine
I felt this would be a useful addition for my THANDAR (Sinclair) SC 110A: compact/single channel/ battery powered/portable, oscilloscope
The metal enclosure is the same physical size (footprint) as the CRO; which sits on top.
A 3 way toggle switch allows display of either, or both (chop) 'channels' simultaneously.
Additional circuitry, provides a +ve earthed 6 volt regulated supply as external DC operation - when internal battery removed from CRO,
and a 25Hz/50Hz/15,625 KHz square wave oscillator to provide reliable external triggering (useful for servicing TV receivers that use these as 'frame' and 'line' oscillator frequencies).