Ampex 351 Catalog Number Index / REV 2 ------------------------------ Prepared by David Dintenfass with help from Peter Haas. Information extracted from various Ampex 351 service manuals and schematics. Address all corrections/suggestions/comments to Dave Dintenfass . Copyright (c) 1999-2024 by David Dintenfass. All Rights Reserved. Revision history Version 1.0 (Nov 1999) Version 2.0 (Feb 2024): added summary section to include additional information about production changes ==================SUMMARY==================================== Catalog 30750: Fixed record and playback EQ; the monitor out jack is fed from the primary of the output transformer; 20 mH coil and associated capacitors in record circuit to compensate for poor HF performance of older tape types; BROWN PHENOLIC BOARDS Catalog 30950: Fixed record and playback EQ; the monitor out jack is fed from the primary of the output transformer; 20 mH coil and associated capacitors in record circuit to compensate for poor HF performance of older tape types. Addition of bias-coupling relay 4K3 (on inside front panel of SLAVE unit) to delay dropout of bias when machine is stopped; this avoids beat notes as the machine drops out of record. BROWN PHENOLIC BOARDS. Catalog 30960: Adjustable record and playback EQ (ceramic trimmer caps and potentiometer(s) respectively); monitor out jack fed from feedback winding of output transformer. 20 mH coil and associated capacitors in record circuit removed due to improvements in magnetic tape by 1960. Bias-coupling relay (see above) included. GREEN FIBERGLASS BOARDS. Transport changes with catalog 30960 included new three-spring brake assembly for better handling with 1.0-mil tape and change to transport control wiring to reduce FF/RW motor torque when reel-size switch in SMALL position. ==================Original info from REV 1=================== 30750-01 master, 7.5/15 ips, hi-z play head 30750-02 master, 3.75/7.5 ips, hi-z play head 30750-03 slave, 7.5/15 ips, hi-z play head 30750-04 slave, 3.75/7.5 ips, hi-z play head 30750-05 master, low-z play head (5T-2 input xformer) 30750-06 master, slow speed, low-z play head (5T-2 input xformer) 30750-07 slave, 7.5/15 ips, low-z play head (5T-2 input xformer) 30750-08 slave, 3.75/7.5 ips, low-z play head (5T-2 input xformer) Notes: There are alternate fixed values of EQ components shown for 7.5/15 ips CCIR versions, but no indication of a separate catalog number for such equalization. ============================================================= 30950-01 master, 7.5/15 ips, hi-z play head 30950-02 master, 3.75/7.5 ips, hi-z play head 30950-03 slave, 7.5/15 ips, hi-z play head 30950-04 slave, 3.75/7.5 ips, hi-z play head Notes: Catalog numbers 30750-x and 30950-x had fixed record and play EQ (though some units have since been retrofitted); there were other minor differences as well. ============================================================= 30960-01 master, 7.5/15 ips, hi-z play head 30960-02 master, 3.75/7.5 ips, hi-z play head 30960-03 slave, 7.5/15 ips, hi-z play head 30960-04 slave, 3.75/7.5 ips, hi-z play head 30960-05 slave, 7.5/15 NAB and 15 AME (three-position EQ switch), hi-z play head, standard bias oscillator 30960-06, see note* below 30960-07 master, 7.5/15 ips CCIR, hi-z play head 30960-08 slave, 7.5/15 ips CCIR, hi-z play head 30960-09 master, 7.5/15 NAB and 15 AME (three-position EQ switch), hi-z play head 30960-10 slave, 7.5/15 NAB and 15 AME (three-position EQ switch), hi-z play head 30960-11 slave, 7.5/15 NAB and 15 AME (three-position EQ switch), hi-z play head, high-performance bias oscillator 30960-12 slave, 7.5/15 NAB and 15 AME (three-position EQ switch), low-z play head (used with head transformer), high-performance bias oscillator Notes: The -09 and -10 versions were used with the 351 transport. The -05, -06, -11, and -12 units are slaves since they were designed for use with the Ampex 300 transport (the ac power connector is on the transport, unlike the 351 transport which gets its ac power from the master electronics). Typically the -11 was used for multi-channel Ampex 300s without sel-sync units, the -12 for multi-channel 300 recorders with sel-sync units (multi-channel meaning any Ampex with more than two channels). The -11 and -12 electronics both feature the high-performance bias oscillator: 12BH7 tube and a tapped primary winding transformer (similar to the "bathtub" 300, the 400 and the 350 in that the feedback comes from taps on the primary and not from a capacitive divider network across the primary). As far as we can tell, the -05 and -06 units had the standard bias oscillator used on all other catalog numbers in the 351 series. The -05 version appears to be similar to the -11 (hi-z play head) but uses a standard bias oscillator (as do all other 351 electronics with the exception of the -11 and -12 versions). We suspect the -06 is similar to the -05 but was equipped with a head transformer for use with a low-z play head. However, we have not uncovered any documentation to confirm this. Tip of the hat to Peter Haas who supplied information for these notes.