1952-3 Gates "Biamote" M-5136 Mic Mixer/Preamp
Well, here's a dusty ol' gem I've had sitting on a shelf for 5 years. Inspired by boredom the other day, I hauled it down and started about cleaning it up, and having a look to see if it would turn on without letting the smoke escape.
This thing dates from either 1952 or 3, and has a worn and crumbling label on the inside of the lid stating a repair date of "Aug 2 1956". Amazing. The only other record of service is "Cleaned pots, May 1960". Some serious work had been done to it though. A 125V mains indicator lamp had been added to the front panel, whatever the original mic sockets were had been removed and replaced with a hunk of sheet aluminium sporting two Canon brand XLR connectors - one for each of the two mic inputs. The mains power cable had been replaced with a 2-prong cable with a Sony embossed molded end. The grounding scheme had been extensively modified, including putting crimped connectors between the chassis front and back, the panel metre, the PS/Circuit, and pin 1 on the XLR connectors.
I brushed and blew most of the cobwebs and dust off and gave it a wipe down. Then, I removed the 2-prong mains cable, and replaced with a 3-prong, adding the power ground to the main chassis node on the back.
There was one yucky looking electrolytic cap on the board, and I replaced that. In addition, there are two 2 section cans, and one 3 section can. I will replace them later.
The tube compliment is 3x5879 9-pin pentodes, and one 12AX7A. Also a 6X4 tube rectifier.
Note the big honkin' output transformer, and the can input transformer! Those two big can looking things on the top right are stepped pots! Insane things. They sure were dirty contacts. I went through about 10 q-tips before they were clean.
I LOVE seeing things with all their important details right one them. So wonderful!
I then decided that since I will NEVER use this as a mixer, that I'd disable the 2nd mic input, and use the jack as an output. I also replaced the unbalanced 1/4inch output jack with a balanced Cliff jack. I just got me one of those old-school Dyno labelers, and naturally had to label the input and output jacks with it!
I held my breath and fired it up. It came up without any smoke. Signal looks lovely and clean. And holy-tits-piles of gain - about 70-90db by my rough estimation. The metre isn't calibrated, as it was pegging out with TONS more clean headroom available. One day, I'll figure out how and where to adjust the calibration for the metre. Also, I need to replace those can caps. I think they're original. That's insane. 60 years old and still quiet...
Some advertising inside the lid. I wonder just how much this thing cost in its heyday...
The only two service tags.
Well, now to try it out on a recording I guess, then do the recap and try it again. I guess these things sound incredible. Warm and coloured and very nice. I can't wait!