In article , Phil
Allison wrote:
Jim Lesurf wrote:



The IM and THD charts that come with the manual are blank and
marked "Disclosure prohibited 4.11.1974"


I must confess I burst out laughing when I read that! Did they think
the detailed distortion performance of their amp was a 'trade secret'
and that no-one should be allowed either to know the spec or measure
it for themselves?!


** The word "prohibited" ought to tell you there was an FCC law in the
USA that prevented making such disclosures.

Why would the Federal Communications Commission prohibit a manufacturer of
audio amplifiers from publishing measurement charts of audio IM/THD?

The same FFC law allowed only continuous RMS power specs and then after
a 1/3 power pre-conditioning session for 30 minutes.

I can recall that the IHFA laid down IHFA-707 specs that required this. Had
to ensure the 700 power amps passed it to keep magazine reviewers happy.
But I don't recall it being mandated by the *FCC*. And the results weren't
then 'prohibited' from being published.

Do you mean FTC? I think the 1/3rd power malarky was their idea to stop all
the American claims for wildly overstated 'output powers'. But I can't
recall any FTC documentation I ever saw that made IM curves 'secret'.

Jim

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