david gourley wrote:
Still have mine, a Heathkit 10-12 (500kc) scope I bought at a Ham Fest 40
years ago. It needs a little TLC, but still very functional.
** That Heathkit model is an "IO-12" with 5 MHz bandwidth.
The fastest sweep is 500kHz.
Always reminds me of the intro to "The Outer Limits" TV show. 
https://www.youtube.com/watch?v=8CtjhWhw2I8
..... Phil