These little plug effects were made by Maxon in the early to late 70's and were sold in Japan under the Maxon brand and outside Japan under the Ibanez brand name.
Plug in effects like this were already being made in the late 60's by several other manufacturers with the most well known being the Electro Harmonix boosts like the Screaming Bird and LPB, both of which would eventually be built into floor units as the idea of plugging straight into your guitar didn't really catch on. The EH versions were initially made, like these with a male plug attached to the enclosure, and then with 2 female jacks so you could rest the unit on your amp (or floor) but still with a slider on/off switch.
The other famous plug in style effect was of course the Dan Armstrong range. Unlike the EH ones, these weren't just boosts (and fuzz) with varying degrees of bass drive. Dan Armstrong had effects like the Blue Clipper, Orange Squeezer, Green Ringer, Purple Peaker, Red Ranger and Yellow Humper, all colour coordinated.
While it's uncertain exactly what year these hit the market they do appear in the 1976 Maxon (and Ibanez) catalogues and I have seen them advertised in Japan claiming to be as early as '71/72? Whatever year they did become available they did not sell very well and didn't last long with them appearing in the '77 Ibanez catalogue and the '78 Maxon catalogue and then disappearing.
They may have hit the market slightly too late as all (or most of) the other brands were making floor units of their circuits by '73 with the "plug in" craze having not really caught on. They're a pretty cool idea and work really well but don't play well with Strats (and some Teles) and other recessed jack guitars.
So, what are they on the inside?
The original EH plug in boosters were all point to point rats nest built with caps and resistors twisted onto a transistor and soldered to the input and output. While these 4 Maxon versions follow the EH circuit almost identically I would never have expected a Japanese manufacturer, especially one as big and intense as Nisshin Onpa to be making rats nest electronics for the consumer market and yes, these are nicely made PCB circuits in typical early/mid 70's Japanese designs.
The circuits themselves are the very simple yet VERY effective boosts based on the original EH design. The only real difference between the 4 versions is the component values, making them anything from a treble boost to a full linear boost with slight clipping. The Distortion Booster has 2 silicon diodes added to ground to clip and compress the signal.
So, everyone familiar with the EH family like the LPB, Screaming Bird and Tree, the Mole, the Ego Boost etc (and of course the Muff Fuzz) will know that this simple single transistor circuit with 4 resistors and 2 (or 4 for bass versions) caps can do so many things depending on what value components you use, and Maxon sure did make the most of it.
While the Ibanez versions were just named 85 to 88 (85 Bass/86 Power/87 Treble/88 Distortion) the Maxon ones are MB - 10 (bass) MB - 20 (Power) MB - 30 (Treble) and MB - 40 (Distortion) with all costing 2.800 JY new.
These are effective little plug in boosts for guitar or bass and apart from the draw back of not playing well with recessed jacks actually work really well. Each one is reasonably well tuned for it's specified job and the battery lasts ...... forever with such a low draw circuit and no LED. Of course, if you're game you can plug 2, or 3, or ..........
Like the EH, Dan Armstrong and other brands these didn't really catch on and take the world by storm. There's not a lot of info out there and they do show up for sale from time to time so if you like those things that are part of something you love but never really made it (I do) then they're pretty cool.