I’m fixing up an HP 143A Wide-Screen Mainframe Oscilloscope, which has a very big selection of plug-ins to provide a variety of functions. The oscilloscope has symmetrical vertical and horizontal circuits, so it can be used as an X-Y amplifier if suitable vertical amplifier plug-ins are installed in each bay. I’m looking to buy 1400-series vertical amplifier plugins like the 1402A, 1404A and 1405A and came across an interesting bit of a mystery while doing research.
HP’s General Purpose Plug-in Oscilloscopes catalog for the 140 system, dated March 15th 1971, lists the 1405A dual trace amplifier plug-in as a DC-5MHz plugin with 5 mV/div sensitivity, more or less a down-rated version of the 1402A plug-in.
In my research I did find a photo of an HP 140B oscilloscope mainframe loaded with an HP 1405A amplifier plug-in…but in this photo, it’s a double height dedicated X-Y amplifier.
That’s definitely a compatible mainframe, shown right in the plug-in guide on the bottom (with the 140A on top, the only difference being a circular vs. square display area.)
This panel clearly fits in the double height 140-system plugin opening, and has the same style of knobs and controls so there’s no question it’s period correct. I’ve been unable to find any mentions of it on the web or at the HP Memory Project.
Personally, I’d rather have a matched pair of 1402A or 1404A vertical amplifiers, which would give me dual- or quad-trace X-Y capabilities instead of the single-trace X-Y with the pictured mystery amplifier, but that’s a very interesting piece of equipment. I’m still looking for another 1402A, or a 1404A – if you have one for sale or know where I might find one, please let me know.