These boards plug into the Playback amplifiers in the electronics package of Ampex AG440 and AG445 recorders.
Ampex Assembly Number: 4020270-01
Ampex AG440B 1/2" 4 Track head assembly, looks new and marked as such, sn 402027305 trapezoidal lap on record head.
Ampex CVC-7 Maintenance Manual for Ampex Betacam SP machines.
The Ampex CVR-35 is identical to the Sony BVW-35. Maintenance Manual Volume 1 in a hard binder.