Rev. Rul. 56-607

In the instant case, certain types of electronic vacuum tubes are designed especially for high power amplifiers with a minimum capacity of 20 watts and for public address and other high power sound systems. They feature low distortion under high power, high overload capacity and high resistance to mechanical shock. These tubes are not known to be used in any amplifier with less than a 20-watt capacity. The cost of the tubes varies from two to three times that of amplifying tubes ordinarily used in radio and television receiving sets and in phonographs. The use of these premium quality tubes in such receiving sets or phonographs would not result in sufficiently improved performance to justify the substantial difference in cost over ordinary tubes. Held, such tubes do not possess actual, practical, commercial fitnees for use in radio and television receiving sets, phonographs, or combinations thereof. Accordingly, sales thereof by the manufacturers are not subject to the tax imposed by section 4141 of the Internal Revenue Code of 1954.