"Can you cite the regulation in which they actually mandated this?
I've never heard of it. "

The both AM and FM thing I remember distinctly due to my exposure to high fidelity. I'm pretty sure
it was in the 1970s. A quick Google does not turn up anything on it though, but that is not uncommon.
Much of this older stuff was simply never archived. Suffice it to say I didn't make it up. I didn't
imagine it.

I find this quite curious, because I subscribed to those same
magazines (Stereo Review, High Fidelity, Audio, the Sensible Sound)
through the same era, and never read or heard anything about that sort
of requirement by the FCC.

I've never seen a reference to such a requirement, anywhere. I've
never seen a receiver, tuner, or integrated circuit described as
complying with a "Part XXX" requirement of this sort (while they're
often tagged as complying with Part 15 rules for RF interference).

I've never heard tell of a manufacturer being cited for failing to
comply, or a bunch of illegal FM-only radios/tuners being seized by
the FCC, or any company fined for selling them.

And, I know there were a bunch of FM-only tuners and radios being made
and sold through that era... Kloss made several FM-only radios, Scott
and others made FM-only tuners, I've still got a Dynaco FM-3 in my
collection (no AM).

So, I'm not sure what you read. It's possible the FCC may have been
_considering_ such a mandate (possibly someone in the AM broadcast
industry filed a petition to ask for a rule-making of this sort) and
this was mentioned in the magazine, but I don't think I've ever seen
any evidence that such a mandate was ever actually implemented. There
_ought_ to have been plenty of traces, visible over the years and even
now, and I haven't seen any.

If it had been I suspect that it might have been unenforceable, as
being outside the FCC's authorized regulatory powers. The FCC has a
lot of authority over what can be _transmitted_, and how, but a lot
less over what can be _received_ (and I think even less over the
question of what must be _required_ to be receivable).

I wonder if I could at least get the date from archives of High Fidelity magazine, to which I
subscribed for a time.

Please pass the info along if you do find it - I'm quite curious.

They used Hirsch-Houck (sp) labs to test everything and though AM was no big
deal they tested it anyway to see if the manufacturer was lying in the manual. Of course the
consistently found poor performance, but then they didn't lie about it. The AM section was there, I
bet some people never ever used it.

I suspect _lots_ of people never used it. Even by the 70s, FM (with
its better performance and stereo capability) had pretty much kicked
AM's butt, as far as quality sound distribution goes.

The presence of the AM section was pretty much a "check-box" item for
most buyers, I think. They expected it to be there (because they were
used to it) and they'd consider a receiver not having it to be
"inferior" and thus less worthy of purchase. That's probably why the
manufacturers (1) continued to include it and (2) didn't bother to
make it a good one - it had to be there to keep their product from
losing sales, but its quality was pretty much irrelevant to those
sales.

The devices which didn't have it, were ones which were being marketed
to an audiophile crowd, I think, where people wanted the best FM sound
for their dollar and didn't care a fig about AM.