SINGER 15-91 - Manual (Page 8)

Do not attempt to unscrew the bulb. It is of the
bayonet and socket type and does not unscrew.
6
To Remove and Replace the Bulb
F
ig
. 2
To remove the bulb. Having turned the shade
slightly, hold the Singeiiight socket with one hand
and with the other hand press the bulb into the.
socket and at the same time turn the bulb over from
the machine as far as it will go, then withdraw
the bulb.
To insert a new bulb. Hold the socket with one
hand and at the same time with the other hand
press the bulb into the socket and turn it over
toward the machine until the bulb pin (B, Fig. 2)
enters the notch in the socket, then return the shade
to its normal position, as shown in Fig. 2.