I like how some of the old lab quality designs are also. I have scrapped a few that were baddly abused or damaged beyond repair from misuse. And have rebuilt a few and sold them also.
The biggest and most interesting one I ever had was a 0-3000 VDC 500 ma unit. It used the same variac to step up transformer design as the smaller step down ones, But instead of diodes it used a pair of vacuum tube rectifiers and a pentode vacuum tube regulator about 4 inches in diameter and 9 inches tall!
I had no use for it so I put it on eBay and sold it. The person who purchased it was so dumb he bid it up to $550 to win it and planned to use it to run a low voltage ham radio transmitter with it.
He even asked lots of questions about it too before he even bid on it. He persistantly reasoned that being adjustable With a maximum output of 1500 watts it shoud be able run his stuff.
It came down to him having no Idea of the differences between amps, volts, and watts!
He got it and tried running his whatever it was and fried everything!
Then reported me to eBay for being a bad seller plus he wanted me or eBay to replace all of his stuff or he was going to get his lawyer involved!
I contacted eBay and told them what went on and they reviewed the sale and said he got what he deserved! My discription was very acurate and my contacts with him specificaly said it would not work for what he needed.
Wish I would have kept it now!
If I come across another one I will next time!