Standard dial lamps:
51B
53B
If handset cord + mounting cord > 15 ft. total, then use:
51A
53A
(51A or 53A can also be used when using 10VAC supply from a Key System.)
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2.07 "Early production handsets will have the lamp in a vertical position, current production handsets have the lamp in horizontal position." ...
5.05 "Lamps carried for maintenance reasons should be of the 53B type since both early and current production handsets accommodate this type."
BSP Section 502-303-101, Issue 1, February 1970, "Reference, 220A Hand Telephone Set, AC1 and AD1 Telephone Bases"
(TCI Library)
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