ribnit and 150 data
David,
Yes, the 61 has a ribnit type of bag. The pattern is verticle and goes about 2 inches of rib and 2 inches of smooth alway the around the bag. The part that says, "Hoover", vertically, is smooth.
Since the 150 was produced for 3 years, I'm not really sure I would call it rare. It is very desirable vacuum for collectors as it had a 2 speed motor, automatic height adjuster, bag full indicator, cushion grip handle and automatic bag tension adjuster. However, it was being made during the depression and was quite costly.
Jeff Parker or Tom Anderson can probably give you specific info on production numbers and other information I am forgetting. I've seen lots of them around over the years but now fewer and fewer. I'm fortunate that I have the complete vacuum with original box, tools, and hose. It took 3 150's to make this one as complete and nice as it is.
The 61 came from ebay, the 64 was a combination of two machines I purchased from VCCC members and the 68 was a gift from my wicked step-sister, Ida Corwin, AKA Fred Nelson. I can't remember the history of the 150 except that the main vacuuum may have come from Fred Stachnik.