This is a Sylvania developmental power pentode in a glass envelope with an eight-pin loctal base. This is a spare tube for Bus Driver Arithmetic Rack S/N 4.
Date
1925 ca.
Identifying Numbers
Model number
SR1407
Printed in silver on top of the glass envelope.
Other number
10-3 13-2
Handwritten vertically in silver ink on the glass envelope.
Other number
XAD4846
Stamped in green ink near the bottom of the glass envelope.
