I've used a number of analog oscilloscopes and my laser for an XY display for the synthesizer. I decided to get a Tektronix 760A Stereo Audio Monitor for my synthesizer as a permanent XY display.
The Tektronix 760A is a half-rack monitor for the studio to monitor, measure, and troubleshoot audio. There were three models vailable and the A model is for a standard dynamic bar graph display response.
There are internal jumpers to set the input impedance and bar graph 0VU reference level including a custom setting. I added the appropriate resistors for a custom setting of 10V pk-pk for my synth.
The 760A was introduced in 1986 and this one was in reasonably good condition. The graticule lights were burned out which is typical. They are rare and expensive mounted in a plastic base. The heat disintegrates the plastic base so I replaced the sockets and used a standard 7381 bi-pin lamp. Right angle 0.125" bi-pin PCB sockets are no longer available so I made mine from a machined- pin DIP socket.
Here is a video of the 760A monitor driven by my E350 Morphing Terrarium.