I own a pair of the 412 guitar cabs. I believe they are the HT4121. I bought a 76 DR201 from one Hi-Tones owners, and he said he thought a pair of these cabs would handle it.
These have a 300W RMS rating, but I can fart one of them out pretty easily with my 79 DR103 if I run bass through it. They are very efficient, so the cab is relatively loud when this occurs. If I remember correctly the problem happens at about Ab/G# on the E string.
Tone wise these are very vintage sounding with bass, as they have the sort of bloomy sound. They are relatively full, but do not produce any real sub bass. The back of the cab has a slot (port), but I don't know if any sort of Thiele/Small tuning was accomplished.
The Hiwatt voicing comes across as really warm for guitar, and bright and scooped with bass. These cabs are fabulous with guitar, very clear and articulate without being bright and ice pickey. I think a pair with bass would be way louder than I would ever need, but some degree of discretion would be required to avoid blowing the drivers. I would be comfortable using the cabs, but not loaning them out to other players.
The Hi-Tone website shows a bass cab that looks just like the HT4121. Same dimensions and grill cloth. Model is HT412 and it's loaded with Eminence Beta 12s. I have never seen or heard one.
Cabinets - Hi-tone Amplification (hi-tone-amps.com)
I also own a Marshal 1960AX/BX full stack loaded with greenbacks. My Hi-Tone cabs can definitely take more power with bass, but they are still guitar cabs and it's important to respect their limits, or you should expect to
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If you don't know, here is how the drivers were developed (as I understand it). One of the precursors to Hi-Tone was a company called Vintage Hiwatt Restoration. These companies were highly involved in the Vintage Hiwatt Convention, which is a fairly large annual get together. I believe there was also an online forum related to the community that attended the convention.
Hi-Tone did auditions at the convention to select the crowd's favorite purple-label Fane driver. Then they had Eminence make several attempted tone clones of the preferred driver. The crowd also selected the driver that was finally put into production. I believe this occurred over multiple years. AFAIK, the cab itself is pretty much an exact duplicate of the Hiwatt design.
The company has since developed a clone of the Fane Crescendo as well.
For the record Reeves also has a purple Fane clone made by Eminence that is well liked. Reeves used different reference drivers, so they are not the same. I own a Reeves 400 and it's fabulous. My impression is Hi-Tone is a more authentic copy of the Hylight era Hiwatts. Reeves are very close, but they have some modern improvements. I do not hesitate to recommend either company