A crapload of patents for rare vacuums!
Here is the first household Birtman vacuum, the ad is from a newspaper in bisbee AZ. This vacuum was NOT made by Bisbee Improvement, but appears to be sold privately through them.
Another EARLY Birtman Vac, they made several similar models, but the only surviving model of the line is the Bee Model D. Shown next to the patent are the pics of the D from the GRPM.
Grouping these three together as I can’t say I know what any of them are, or if any examples are still around. If you know anything about any of them, please speak up!
I’m almost positive this is what became the first Apex, the resemblance can be seen in the 2nd patent. Come to think of it, that first Kirby patent may be an improvement on this...