21ATP4A electron tube manufactured by Sylvania, listed as 21ATP4A (circa 1959).

21ATP4 electron tube manufactured by Sylvania, listed as 21ATP4 (circa 1959).

21AQP4 electron tube manufactured by Sylvania, listed as 21AQP4 (circa 1959).

21AP4 electron tube manufactured by Sylvania, listed as 21AP4 (circa 1959).

21ANP4 electron tube manufactured by Sylvania, listed as 21ANP4 (circa 1959).

21ALP4B electron tube manufactured by Sylvania, listed as 21ALP4B (circa 1959).

21ALP4A electron tube manufactured by Sylvania, listed as 21ALP4A (circa 1959).

21ALP4 electron tube manufactured by Sylvania, listed as 21ALP4 (circa 1959).

21AFP4 electron tube manufactured by Sylvania, listed as 21AFP4 (circa 1959).

21ACP4 electron tube manufactured by Sylvania, listed as 21ACP4 (circa 1959).

20MP4 electron tube manufactured by Sylvania, listed as 20MP4 (circa 1959).

20HP4D electron tube manufactured by Sylvania, listed as 20HP4D (circa 1959).

20HP4C electron tube manufactured by Sylvania, listed as 20HP4C (circa 1959).

20HP4B electron tube manufactured by Sylvania, listed as 20HP4B (circa 1959).

20LP4 electron tube manufactured by Sylvania, listed as 20LP4 (circa 1959).

20HP4A electron tube manufactured by Sylvania, listed as 20HP4A (circa 1959).

20HP4 electron tube manufactured by Sylvania, listed as 20HP4 (circa 1959).

20DP4C electron tube manufactured by Sylvania, listed as 20DP4C (circa 1959).

20DP4B electron tube manufactured by Sylvania, listed as 20DP4B (circa 1959).

20DP4 electron tube manufactured by Sylvania, listed as 20DP4 (circa 1959).