Extra octal socket on M-series amp & M-22 schematic

[amsaunders]

I have an old M-22 chassis that needs to be rewired. Does anybody have a M-22 Schematic? Also the amp has an extra octal socket which doesn't look like it was used for the power tubes or rectifier but appears to be factory installed. The extra socket is located between the phase inverter and the first power tube. I seem to remember seeing this socket on some photos of other larger wattage M-Series amps, but I am at a loss to what its purpose is. Any ideas? Also I am assuming that the power transformer for these larger amps was mounted on the main chassis and not on an aux chassis as in the B-series amps, it that also correct?

[grazioso]

power tranny and big can multicaps and sometimes rectifier were on the bottom of the cab on separate chas. so the octal is exacatly there for that - connector between upper and lower.

[tracy]

On my M22, it's the speaker socket. Wires should be coming from the output xformer, taps available for 2, 4, and 8 ohms as well as 70 volt line.

[redtoploader]

What Tracy said...on my M16, the extra octal is for the speaker out. Weird setup.

[jingle_jangle]

Not weird at all, for older rigs. In fact, fairly common with the old "metal box" style PA amps that were used in the '30s and '40s, and now commonly sold as "harmonica" amps, as Little Walter, among other players, favored these and they were a big part of the distorted sound of blues harp players. We knew not to push them, as generally they did not have a very "creamy" breakup at high gain settings.

In the '60s these were cheap and readily available, and my bands went through a half-dozen of them at least. Virtually all of them had single or double octal speaker jacks. I remember buying male octal plugs from Allied Radio in Chicago, and wiring these with zip cord. There was always a selector for impedance, with a 70V "balanced" line as one option.