Atwater Kent Service Data for Models 70, 74, 75, & 76 and N, N-3, J, & JB Speakers
Service Manual pages 217-256

Atwater Kent published the information for all variants of these radios organized by chassis letter, which is the suffix letter following the model number. Page 218 has a good chart of models and their components.
Note: The Model 72 (H chassis) is covered in a separate document (SM Jan 1931 pages 257-280).
See note following table regarding different versions of L, D and Q chassis.

Literature Title Date Page(s) Model(s) Description
Service Data Dec-1930 217 All Document index
Service Data Dec-1930 218 All Table of sets & speakers
Service Data Dec-1930 219 All Important Service Notes
Service Data Dec-1930 226 All Variable condenser & RF coils
Service Data Dec-1930 220 70-L 74-L 76-L Schematic & voltage table (L-1 chassis)
Service Data Dec-1930 222 70-L 74-L 76-L Component parts (L-1 chassis)
Service Data Dec-1930 223 70-L 74-L 76-L Chassis underside view (L-1 chassis)
Service Data Dec-1930 221 70-L 74-L 76-L Schematic & voltage table (L-2 chassis)
Service Data Dec-1930 224 70-L 74-L 76-L Component parts (L-2 chassis)
Service Data Dec-1930 225 70-L 74-L 76-L Underside view (L-2 chassis)
Service Data Dec-1930 227  228 70-L 74-L 76-L Parts list
Service Data Dec-1930 229 70-L 74-L 76-L Miscellaneous parts & hardware with illustrations
Service Data Dec-1930 230 70-F 74-F 76-F Schematic
Service Data Dec-1930 253 70-F 74-F 76-F Voltage table
Service Data Dec-1930 232 70-F 74-F 76-F Parts details
Service Data Dec-1930 233 70-F 74-F 76-F F chassis underside view
Service Data Dec-1930 241b 70-Q 76-Q Schematic
Service Data Dec-1930 241a 70-Q 76-Q Voltage table & service notes
Service Data Dec-1930 242 70-Q 76-Q Parts details
Service Data Dec-1930 243 70-Q 76-Q Wiring diagram (Q-2 chassis)
Service Data Dec-1930 244 70-Q 76-Q Top view & parts list
Service Data Dec-1930 245 70-Q 76-Q Wiring diagram & parts list
Service Data Dec-1930 246b 74-D Schematic (D-1 chassis)
Service Data Dec-1930 247b 74-D Schematic (D-2 chassis)
Service Data Dec-1930 246a 74-D Voltage table & service notes (D-1 chassis)
Service Data Dec-1930 248 74-D Parts details
Service Data Dec-1930 252 74-D Wiring diagram & parts list
Service Data Dec-1930 253 74-D Misc parts
Service Data Dec-1930 250 74-D Wiring diagram (D-1 chassis)
Service Data Dec-1930 251 74-D Top view & parts list (D-1 chassis)
Service Data Dec-1930 247a 74-D Simplified voltage distribution (D-2 chassis)
Service Data Dec-1930 249 74-D Wiring diagram (D-2 chassis)
Service Data Dec-1930 231 75-P Schematic (voltages on pg 221)
Service Data Dec-1930 234 75-P P component parts
Service Data Dec-1930 235 75-P P chassis underside view
Service Data Dec-1930 236 75-P Phonograph pickup
Service Data Dec-1930 237 75-P Motor & brake adjustments
Service Data Dec-1930 238 75-P Parts location photos
Service Data Dec-1930 239 75-P Parts list
Service Data Dec-1930 240 75-P Troubleshooting chart
Service Data Dec-1930 254 Speakers All Centering top pole piece
Service Data Dec-1930 229 Speakers All Miscellaneous parts & hardware with illustrations
Service Data Dec-1930 255 Speaker J Parts list
Service Data Dec-1930 255 Speaker JB Parts list
Service Data Dec-1930 254 Speaker N Parts list
Service Data Dec-1930 255 Speaker N-3 Parts list
Service Data Dec-1930 256
(blank page)

Two versions of the L chassis (L-1 & L-2) split at serial number 6,234,881.
Two versions of the D chassis (D-1 & D-2) differ only in the arrangement of screen resistors.
Two versions of the Q chassis (Q-1 & Q-2) differ only in the use of an output choke and condenser.