47 CFR §97.315

1. (a)Any external RF power amplifier (see § 2.815 of the FCC Rules) manufactured or imported for use at an amateur radio station must be certificated for use in the amateur service in accordance with subpart J of part 2 of the FCC Rules. No amplifier capable of operation below 144 MHz may be constructed or modified by a non-amateur service licensee without a grant of certification from the FCC.
2. (b)The requirement of paragraph (a) does not apply if one or more of the following conditions are met:
   1. (1)The amplifier is constructed or modified by an amateur radio operator for use at an amateur station.
   2. (2)[Reserved]
   3. (3)The amplifier is sold to an amateur radio operator or to a dealer, the amplifier is purchased in used condition by a dealer, or the amplifier is sold to an amateur radio operator for use at that operator's station.
3. (c)Any external RF power amplifier appearing in the Commission's database as certificated for use in the amateur service may be marketed for use in the amateur service.