With the then rapidly decreasing presence of MC inputs on amplifiers, Sony put out miniaturized step-up transformers... plug-ins ! Long gone were the HA-55, the very briefly available ESPRIT lookalike HA-T1 or the rare HA-50 - why make big when small is available ?
Just hook your turntable's MC output into those tiny plugs and the latter in your amplifier's MM stage - et voilà !
The three models share the same specs with only distortion gradually increasing in level on the lower models and the T50 sporting an Amorphous Core bonus.
The HA-T10 are easy to find, the T30 and T50 are very rare. Pretty much sought after, even in Japan so I guess these must do their duties well.
The HA-T10 was also available at Ortofon, under the T-5 name and by Empire under the ET-1 moniker. Since Sony had higher-up models and not Ortofon (in such format), I guess Sony handled the manufacturing for Ortofon which, in turn, did something else for Sony...