The M2 was the smallest, least expensive amp of the Custom Series.
|Power||2x 6GW8 (power and phase inverter)|
|Vibrato||12AU7, (1/2) 7025, 2 varistor|
The M2 has simple volume and tone controls and a F.M.Vibrato unit mated to a single 8" speaker. Vibrato has speed and depth controls and a footprint jack. This was the entry level model and probably best suited for accordion and guitar.
The M4 is almost a M2 with reverb.
Because the 6GW8 contains a power pentode and a triode in the same glass envelope, Magnatone could use the two triodes for a phase inverter and install one less 12AU7 in the amp, thus lowering the manufacturing cost of these entry level amplifiers.
The M2 might have been dropped from the catalog when the Starlite Series was released in 1964. The 421 is very similar to the M2.