A co-worker just got a PC1250A from Sharp, vintage 1982 or so. It’s the size of a calculator, has a one-line display and ROM Basic, and comes with 4K memory and a one-line display. He also has the base station with a micro-cassette tape drive and a paper-tape thermal printer.
(Hey, it was free!)
The problem is that, while he has manuals for the base station, he has none for the computer itself. He can figure a lot out from the sample programs (on tape and listed in the base-station manual), but would like to find a real set of manuals. He has searched the Web and found lots of other stuff, but not the manuals.
From the description of the base station I would guess that it is a slightly different model than the TRS-80 which IIRC did have an accessory to interface with a regular cassete player but no base station as such. The TRS-80 was the same as a slightly older and larger Sharp model. If I am correct then the manual pointed to by astro will still be of some use as there were only a few differences in operation between the two.
While the “base” options may differ I think the P-3 is more or less identical to the 1250a. Tandy made several pocket computers (including the P-1 and P-2) and most were Sharp OEM units which may be the older/larger units you are thinking of.
Looking at the clerer picture I suspect you may be correct. The picture in your earlier link was unclear and looked more like the bigger, older model I alluded to. This was partly due to a bias on my part because Tandy (what Radio Shack was called in the UK) did not seem to stock the better models.