21FP4C electron tube manufactured by Sylvania, listed as 21FP4C (circa 1959).

21FP4A electron tube manufactured by Sylvania, listed as 21FP4A (circa 1959).

21FP4 electron tube manufactured by Sylvania, listed as 21FP4 (circa 1959).

21DEP4 electron tube manufactured by Sylvania, listed as 21DEP4 (circa 1959).

J171 electron tube manufactured by Sylvania, listed as J171 (circa 1959).

21CWP4 electron tube manufactured by Sylvania, listed as 21CWP4 (circa 1959).

21CXP4 electron tube manufactured by Sylvania, listed as 21CXP4 (circa 1959).

21CUP4 electron tube manufactured by Sylvania, listed as 21CUP4 (circa 1959).

21CQP4 electron tube manufactured by Sylvania, listed as 21CQP4 (circa 1959).

21CMP4 electron tube manufactured by Sylvania, listed as 21CMP4 (circa 1959).

21CEP4 electron tube manufactured by Sylvania, listed as 21CEP4 (circa 1959).

21CBP4 electron tube manufactured by Sylvania, listed as 21CBP4 (circa 1959).

21AYP4 electron tube manufactured by Sylvania, listed as 21AYP4 (circa 1959).

21AWP4 electron tube manufactured by Sylvania, listed as 21AWP4 (circa 1959).

21AVP4B electron tube manufactured by Sylvania, listed as 21AVP4B (circa 1959).

21AVP4A electron tube manufactured by Sylvania, listed as 21AVP4A (circa 1959).

21AVP4 electron tube manufactured by Sylvania, listed as 21AVP4 (circa 1959).

21AUP4B electron tube manufactured by Sylvania, listed as 21AUP4B (circa 1959).

21AUP4A electron tube manufactured by Sylvania, listed as 21AUP4A (circa 1959).

21AUP4 electron tube manufactured by Sylvania, listed as 21AUP4 (circa 1959).