|Years||1963½-1964 (1965 see M13A)|
|Power||2x 6CA7 (EL34)|
|Power Bias||fixed bias|
|Vibrato||12DW7, 12AU7, 4 varistors|
|Speaker||15" 8ohm Jensen|
|Speaker||4x 3" 4ohm|
|Output Trans||3.5K:8ohm and 4ohm|
|List Price||$820 (Dual Imperial)|
The M12 and the M13 are a unique pair of Magnatone Custom
series amps as they both use 6CA7's (EL34s). The M12 is a basic two
channel bass amp, but the M13, on the other hand, is feature rich!
It takes the M10 and adds channels, features, and speakers.
The M13 has three input channels!
F.M.Vibrato is only available on channel No.1. Along with "Treble" and "Bass" controls, channel No.1 has a four position "Contour" Switch that selects between "mellow", "normal", "brite", and "treble plus" tone settings an extra 7025 triode section to make up the gain from this extra selectable tone stack. This very unique feature was probably first seen on the 1959 190, and was adopted in 1965 to the M10A and M15A amplifiers.
Channel No.2 has a "Loudness" and "Tone" controls in addition to
a three position "Contour" switch. This channel uses one section of
a 7025, and the "Contour" control is similar to the one used on
the M13's contemporary stablemates, the 1963-1964
Channel No.2 and Channel No.3 mix together and share a triode gain stage before hitting the phase inverter.
Channel "Three" has only "Loudness" and "Tone" controls. It has two input jacks labeled "Mic" and "Bass", but these two inputs are mixed together before they hit the first gain stage, so really, its just about input impedances.
The M13's reverb is all tube reverb with a hammond style spring tank. Parallel stages of a 12AU7 drive the tank, and 1/2 a 12AX7 is used for recovery. All three Channels have input level control knobs, and the final output has a "master" reverb level (pretty slick!). While the M13's stablemate M10 and M15 amps used a transistor (which was a design carry over from the 480), the M13 was all tube. This design proved to be a good one, as the M10 and M15 would adopt a similar design later in 1965.
It is possible that the M13 was targeted at the band that wants a single amp for guitar, accordion, and bass, with the spartan third channel aimed at the bass player. In 1963, mobile PA systems were in their infancy and Magnatone thought there was market for a amp where six musicians could plug in. They aren't very common, and its hard to say why they thought this was a good idea, but it makes for a cool amp.
The 6CA7's are also octal plug tubes, so larger holes were needed in the chassis, thus the M12/M13 chassis was a one off initially, then at some point they made a shared chassis that took both octal and noval power tubes (for the M10, for example). The 6CA7 has a much high plate dissipation than the 7189, so the 6CA7 was probably used instead of the 7189 for a higher wattage output.
The M13 came with a single Jensen 15" speaker and, usually some tweeter speakers. The early M13's came with four 3" tweeter speakers, but the tweeter arrangmeent was changed over time. Unlike the other 15" amplifiers in this series, I don't think a 15" Oxford was ever installed in an M13.
The M13 has a unique distinction among Custom Series amps of not having an "M13" badge (or illuminated escutcheon as Magnatone referred to it!), instead the badge says "Magnatone". Also, somewhat unique was an additional name given to the M13, "the Imperial". Between the lack of "M13" on the control panel and the lack of it on the badge, one might spectulate that someone at Magnatone said "13 is an unlucky number and we can't brand the amp an M13!".
Production of the M13 began in the summer of 1963 and ran through 1964. It was replaced in 1965 with a new version, the M13A, and by 1966, the M13A was dropped as the M20 was added to the catalog (The M20 and M13 were both available concurrently for a short time).
While the M13 was known as the "M13 Imperial", Magnatone also offered an "M13 Dual Imperial" which was an Imperial paired with the RS-2 15" matching extension cabinet.
Special thanks to LeonC for the pictures of his M13.