|Years||1965-1967 (maybe as late at 1968)|
|Tubes||14 novals, 4 octals.|
|Power Bias||fixed bias|
|Preamp||6x 12AX7, 1 7247, 5x 12AU7|
|Reverb||spring tank, tube recovery|
|Vibrato||4x 12AU7, 2x 12DW7, 8 varistors,|
|Phase Inverter||2x 12DW7 or 2x 7247|
|Speaker||4x12" (or) 2x15"|
|Output Trans||3.5K:8ohm and 4ohm (4ohm tap not used)|
|Output||(2x) 40 watts|
|List Price||$1090 with RS-4 cabinets (1965)|
|List Price||$1290 with RS-5 cabinets (1965)|
|List Price||$825 (1966)|
|List Price||$1350 (M20DL) with RS-15 cabinets (1966)|
|List Price||$1190 (M20) with RS-12 cabinets (1966)|
The M20 first appeared in the fall of 1965. It was the top of the line Magnatone amplifier and was certainly the height of Magnatone circuit complexity. It is the only amp in the Custom series that did not install speakers in the main amp cabinet. Speakers came as a pair of extension cabinets, in either 1X15" or 2X12" speaker formats. With two instrument inputs and two mic inputs, it was obvious that Magnatone had this to "up sell" M13 owners who needed bigger and louder. This was a PA and instrument amp all in one, incorporating nearly every bit of engineering that exists in all the models in series. It was expensive with a list price of $1090 when it debuted in 1965.
Special thanks to David Gant for providing the photographs of this M20.
Special thanks to George Nichols and Brunswick Amplifiers for providing this photograph.
This impressive M20 display showcases a Magnatone Tornado guitar along with two 2x12" extension cabinets with matching red royalite tops and black sparkle vinyl covering (visable in the side pics). Later in production, after the Pro Series came out, the extension cabinets available with the M20 were changed to share with the MP4 and MP5 (See extension cabinets for more information).
Notice the black sparkle vinyl finish and three foot switches: one for vibrato and two for reverb.
The M20 changed its model name to the M20A without a major circuit change probably sometime in late 1965. There were two different back-lit escutcheon badges. Some M20's use the M13 "Magnatone" and some used "M20" badges.
Very few of M20s were made. They were excellent trade show items, but very expensive. From late 1965 through 1967, production probably numbered between 20 and 50. This was the only Custom Series amplifier to come with both red and black Royalite tops, and the only one to come with a sparkle vinyl finish (red top 1965 models).
Initially the M20 was available with either a pair of RS-4's, which were 2x12" cabinets with royalite tops to match the M20, or with a pair of monster RS-5 2x15 cabinets borrowed from the new Pro Series.. As some point, maybe in 1966, the RS-4 cabinet was dropped and the RS-5 became RS-15's. The M20 Deluxe (M20DL) came with the two large RS-15 cabinets, and the standard M20 came with two RS-12 cabinets. See Extension Cabinets for more details.
There are five inputs: two mic inputs, two instrument inputs, and a bass input. The bass input has volume and tone controls, the two mic inputs each have volume and tone controls as well. The two instrument inputs have volume, treble, and bass controls as well as a contour switch.
There are two reverb controls, one for each "speaker channel" as labeled on the control panel, however both use the same reverb tank (each control adjusts the input level into the tank independently, and those controls are buffered with triode stages -- really pretty slick).
The amp is enough of a monster that two power transformers are used. The B+ is summed together, but the filaments supply of one transformer is for the filaments of the power tubes, and the filament supply of the other transformer is for the preamp chassis. The M20's lower chasis housed all transformers and the four power tubes.
Special thanks to David Gant for the above black M20 pictures. David is looking for the correct RS2, RS-12 or RS-15 cabinets. if you have a lead for David, please contact me.
This M20 was recently serviced by Brunswick Amplifier in Ohio. Written on the inside of the chassis were the words "M20 Sample". The inside of the cabinet gives the appearance that it was made from scrap wood (odd channels and routed areas that didn't pertain to the contruction of the cabinet). The grill cloth looks to be the same used on the later Pro Series amps. left Harmony in later years, or a pre-production test unit. If you can shed any light on this, please contact me!.
See Extension Cabinets for descriptions of all cabinets available for the M20.
Schematic: M20 NEW
Magnatone evidently gave M20 setups to pop groups that donned matching outfits. Who else could afford them? One of these pictures is from 1967, so Magnatone was still using the M20 as its flagship in press relations:
This fantastic press photo show the entire Magnatone line-up! The organ might be a M-101, and the left Custom might be an M12. At the flanks are the large RS-15 cabinets that were available with an M20. That might be 400 pounds of equipment, its a godo thing there are six guys here!
Its hard to tell if this is a black or red Royalite M20 setup. These amplifiers were used for 14 hours by 14 bands at a Toronto show put on by Canadian Magnatone distributor Hough & Kohler.
This press release sent to Billboard magazine in 1967 is pretty funny. Evidently if you bought a $1300 amplifier they gave you this $30 sign.