Magnatone Guitars!

New for Fall 2013, a complete guide to Magnatone guitars and the stories behind them!

1938-1960 Steel Guitars

1956-1963 Bigsby/Barth Era

1964-1966 Starstream Era

 

Magnatone Custom M12, M12A

Special thanks to George Nichols and Brunswick Amplifiers for providing this photograph.

 

Years 1963½-1966
Series Custom Series
Channels two
Power 2x 6CA7 (EL34)
Power Bias fixed bias
Preamp 2x 7025,
Phase Inverter 12AU7
Speaker 15" 8ohm
Rectifier solid state
Output Trans3.5K:8ohm and 4ohm
Output 80watts peak
Weight 58 lbs.
Height 26.5"
List Price $400

The Magnatone M12 was a powerful bass combo amplifier designed in 1963 and produced until 1967. Two 6CA7/EL34 power pentodes supplied 85W peak output to a single heavy duty 15" speaker. The M12 had two input channels, and an extension speaker jack for an optional extension cabinet.

The M12 was one of two bass amplifier models in the newly designed Custom Series line of premium amplifiers (The other bass amp, the M7, was a single channel 38W peak amplifier). Both the M7 and the M12 were designed and released in 1963 by Chief Engineer Tony Price and Jim Evans. These both sold well for Custom Series amps, much better than the bass amps they replaced (the 425 and 435).

A central aspect of the M12 was it's use of 6CA7/EL34 power pentode tubes and push-pull output transformer with a 3500Ω primary winding. Except for the similarly designed M13, all other Magnatone amps used smaller 7189A's with an ultra-linear transformer. Both of the power supply design changes came in 1963 as a necessity to produce more powerful, louder amplifiers with lower overall costs.

M12 and M13s were fitted with a heavy duty ceramic 15" Jensen speaker. Initially, the M9 and M7, also 15" speaker amps, were fitted with smaller Oxford speakers.

M12 variations

The 1963-1964 M12s had "Loudness" and "Tone" controls for each channel. At some point, maybe in 1964 but certainly by 1965, each preamp was re-engineered to have both "treble" and "bass" in a Baxandall arrangement.

Special thanks to George Nichols and Brunswick Amplifiers for providing this photograph.

 

Color Change

Like all Custom Series amps left in the catalog for the 1965 re-vamp, the gold control panel and gold grill cloth was changed to a polished aluminum look with silver grill cloth around March 1965. The tone stack was changed (see above) at this time as well. At this time, the M12 became the M12A (although this was more of an internal designation change with Estey).

Replacement Parts

The M12A power transformer is a 330-0-330v with a 36v bias tap. Given that Magnatone rationalized transformers (and other parts) across all amps as much as possible to maximize buying power, the same transformer was likely used on the M13A and possibly the M10A and M7A. In general, because the availability of both power and preamp tubes, and the fact that the output transformer was not an ultra-linear type, the M12 is possibly the most servicable of all the Custom Series amps.

 

This is a dealer brochure from sometime in 1966 showing what the dealer paid, and what was suggested for a retail price. The nickname, "The Brute" was light-hearted and aimed at a youth market.

 

DA/MagnatoneAmps.com

 

 

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