The tubes in them are not teenie-weenie, but Neutrodyne receivers are early tube-based radios that used batteries, and were tuned with three large knobs in front. Completely different tuning concept from modern receivers, based directly on how the tubes themselves function.
The 1923 Stromberg-Carlson Neutrodyne I have used 1.5V, 45V and 90V batteries. Ever see a 90V 'voltaic cell' array? Neither have I, except in a pic. They used acid-bath wet cells for batteries back then. Nothing like a minor hazardous chemical plant in your living room, just so you can hear a radio station!
Definitely not portable!
There is a company out there that makes specialized transformers specifically for powering these early tube-based receivers off of mains voltage, but they are rather expensive.
The so-called "portable" ones I've seen were like toting a set of luggage around. Portable meant you could put them in your car and haul them to a picnic site, not that you could carry them around with you on a stroll. I've never seen a really small portable based on that early technology, but it sounds to me as if that may be what you found.
Any chance of pics?