Ampex 6973 (1958–62?)
A pair of tube-powered monoblock amplifiers using 6973 output tubes, built for the Ampex Crescendo Home Music System.
Overview
The Ampex 6973 is a monoblock tube amplifier from the Ampex Crescendo Home Music System, developed in the late 1950s. Each unit uses a pair of 6973 output tubes in push-pull, with a 7199 tube handling the front end. One owner noted that the 7199 can be swapped for a 6U8 with an adapter. That helps, since the 7199 is scarce today. According to owner measurements shared on diyAudio, the amplifiers deliver 21.5 watts with a total harmonic distortion of 1%. The original Triad output transformers are often kept during restorations. Rebuilds typically mean complete rewiring, new sockets and replacement capacitors.
Design
The 6973 uses a cathode-biased push-pull circuit. One builder described it as "essentially a Mullard circuit," which suggests British design influence. The chassis carries custom-wound Triad output transformers, and they are kept even in full rebuilds. The other internal parts are frequently renewed, but the transformers are considered integral to the amplifier's character and are left alone.
Context
The 6973 was produced circa 1958 to 1962 as part of Ampex's short-lived Crescendo Home Music System. It moved the company, a leader in professional tape recording, into the high-end consumer audio market. No direct competitors or market positioning details survive in the record. The matched monoblocks and high-quality transformers point to a premium-tier product for its era.
Market
Restoration is common, with owners typically replacing all components except the original transformers. The need to replace the rare 7199 input tube is a recurring theme, prompting substitutions with more available types like the 6U8. Stereophile (December 1981, p.117) observed that "many vintage tube amps from this period require complete reconditioning to perform reliably," a statement that applies directly to the 6973’s current survival and usability.
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