A few years ago at an estate sale, I picked up a bunch of photo equipment - mostly darkroom odds and ends but also a box of glass slides of national parks. I needed to find something to project them and happened on a boardroom projector of probably 1950's vintage that would do up to 3x4 inch slides. It was a high quality corporate grade American Optical projector in a nice metal case with 5 lenses (Spencer, B&L etc) of different lengths and several bulbs of different wattage to match the length of the lenses and a couple of slide carriers. It was perfect for the slides I had and I figured I could glass mount my 6x9 transparencies too if I wanted. Never got around to that then but thinking about it now I just might. Oh, it cost me $40. I just looked on eBay and saw a simple Besseler one for $25 and a couple of AO's that were probably WWII training vintage that were $45.