Gibson EH-150 square/round corner cab speaker questions

[murrayatuptown]

I saw a photo of an EH-150 interior that had a 12" Ultrasonic Reproducer stamped 12F2. I have seen a number of rubber stamp ink markings on other speakers that I want to believe 'suggest' Jensen-style p/n's but they do not appear in old catalogs.

The number 12, or 10 appears to simply be the speaker nominal size. I have a mid-30's Coronado speaker made by Jensen that has a model number Weber uses for a PM speaker in the 2020's, and it's TOTALLY coincidental. A pair of Capehart by Jensen also have '12' prefix but the full p/n is not found in Jensen catalog scans.

The latest field coil speaker I took in for repair was described as 14", and the front circular diameter does measure 14-3/8". The the widest part of the cone where it's glued to the basket is barely 12.5", and the surround pleats are only 10-3/4"...so that 14" is 'marketing size', like measuring a TV screen by the diagonal of the cabinet. The tech said he'd call that a 12" for quote purposes. That is actually stamped 12J70x. Can't find that in Jensen history. It has two different Zenith p/n's. Tech says Zenith made their own assemblies, but could have bought the basket stampings from Jensen.

I also got 2 pairs from two different generations of Hammond organ cabinets. Two from M1, M2 or M3. I haven't figured out what Hammond cabinet the older ones came from.

One is a pair of Jensen Concert A-12's that are a set, Hammond p/n's AO15888 5 and AO15888 6 with very different field coil resistances. That had me worried, but I found the exact same thing in a Hong Kong BBS sale listing in Chinese and let Google Translate reveal they had the same nominal resistances. Those could be older because they have no EIA manufacturer codes & date codes in the newer format.
The other pair are both Hammond AO21055-2. Those are the 40's ones, one being a Jensen 220717 F12NS. The other is a Rola 285xxx (I forget the date and the details are in the box with it. I don't remember if it says F12NS, but has the same Hammond p/n).

I'm not trying to restore or replicate the Ultrasonic Transducer, but am interested to figure out what the heck a 12F2 was. It will be interesting whether a menagerie of 12" field coil speakers sound as different as the wide range of PM speakers people can choose from now. The voice coil power rating was tiny in the 30's (8-9-10 W was common, but some of the larger Jensen's had higher ratings...I don't think I've seen anything over 20 or so W. The Gibson one could have secrets behind the 12F2 pedigree.

[murrayatuptown]

My reconing tech says Ultrasonic Transducer field coil speakers were made by Utah.