McIntosh 240 (c. 1960–1961)

The McIntosh 240 is a vacuum-tube stereo power amplifier from the very early 1960s. Not much about it is documented. What exists comes from a series of advertisements that ran in High Fidelity magazine between September 1960 and March 1961 (e.g., September 1960, p.31; October 1960, p.17). Those ads called the 240 "the finest performance available in a stereo power amplifier" and pushed its cool operation. It was said to stay well within tube manufacturers' long-life recommendations, with the transformers running noticeably cooler than comparable units, as noted in High Fidelity (September 1960, p.31).

Past that promotional copy, the record is thin. The ads are the main surviving source, and they describe a practical, flexible design:

Power output: 40 watts per channel in stereo, or 80 watts in mono (bridged mode).
Input sensitivity: Multiple sensitivity ranges to accommodate any preamplifier, stereo or monophonic.
Outputs: Accommodates all voice coil impedances, plus 600-ohm and 70.7-volt lines.
Price new: $288, which included the cage (per five separate ad runs in High Fidelity from late 1960 to early 1961).

No production years, circuit details, dimensions, or weight have been confirmed outside these advertisements.