1970 AMPEG SVT
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Ampeg continued transitioning the two front power switches from plastic to metal (with one, or both black). All three versions of switches were used in 1970 (both plastic, both black metal, one chrome and the other black metal). During the year (by serial #100200) painting the inside of the wooden box black became standard and Ampeg also began to paint the chassis black. The preamp and chrome chassis were usually hand numbered with matching numbers until chassis painting began. The chassis featured a standby interlock for part of 1970 only. The interlock was located under the front grille and looked like a two prong power outlet/jack, but was actually a safety standby feature. During the year (by serial # 10020x) the metal cord wraps on the back increased from two to four. Late in the year the year Ampeg changed the six power tubes from "bottleneck" 6146B's to 6550's.
Other 1970 SVT characteristics: "Blueline" silkscreened graphics with detail etched into the metal, two channels, small black "D shaft" knobs with silver tops, black plastic tone adjustment rocker switches, small round red power light, silver grille cloth, exposed plastic fan, two prong power cord and outlet, fuse, 4 pin XLR speaker cable and jack, Linden manufacturing, (3) black transformers: power, filament and output, circuit boards, capacitors, CTS potentiometers with both plastic and metal "D shafts", vinyl handles, smooth vinyl covering, tube chart sticker, manila envelope containing schematic, six rubber feet, eight chassis connector bolts, 8x10 inch speaker cabinet with unpainted face and metal bullseye logo, three handles, CTS speakers and matching dolly, literature.
In 1970 SVT serial numbers were stamped into the chassis, seen through a "cutout" in the middle of the removable back panel. The cutout was located between the standby switch and the external amp jack. Ampeg 1970 serial numbers started around 93000. However, Ampeg serial number dating is undocumented and very difficult. Some examples of 1970 SVT serial numbers are 09477x, 09581x, 10025x, 10062x, 10071x, 10251x, 00515x and 00523x. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor and speaker codes.
Component code dating vintage SVT's: As with all vintage gear, the manufacture date is determined by the newest component/date stamp on the unit. On vintage SVT's, the newest date code on the unit is usually the four digit white ink stamp on the large output transformer. The first two numbers indicate the year, the third and fourth numbers indicate the production week of that year. Example: 7037 means a transformer made in the 37th week of 1970.
Other codes to determine the manufacture date: The other large power transformer and the adjacent smaller filament transformer should both have six digit codes stamped into the metal. The first three digits indicate the company's personal manufacturing code. Those should be 682, which indicate the Electrical Windings Company. The fourth number indicates the year. The fifth and sixth numbers indicate which week of that year.
Potentiometers are also date encoded. There is a seven digit code stamped into the metal. The first three digits indicate the company's personal manufacturing code. Those should be 137, which indicate Chicago Telephone Supply or CTS. The fourth and fifth numbers indicate the year. The sixth and seventh numbers indicate which week of that year. Capacitors and speakers can also be dated in a similar manner.