Let's have a look at a couple drum machine sections from the organ donor pile.
Here's the drum accompaniment section from the Wurlitzer 4373. This one stands out as being a contender for rehousing due to its compact nature. Pattern selection is achieved via rocker switch as opposed to radio buttons, so stacking up genres does not require a deft hand.
In looking at the neatly stacked PCBs at left, I believe we've got analog sounds at top and digital logic amidst the spread of ICs on the lower PCB. I dig the simple user interface on this thing, visualizing it in a dark wooden enclosure is a snap.
Here are the auto accompaniment modules for a (near as I can figure) 1969 Thomas Organ, each self contained in a stapled shut press-board enclosure.
The "Playmate" was less than forthcoming with offering up a top side gut shot, what with the staples and all, but I'm going to guess that this perspective is actually the more interesting of the two anyway. I believe the circuit board at left contains the sound module portion of things, based on the type of wire connecting. Looks like four primary sounds that are mixed into a drumset (noise and high-mid-low oscillators would be my guess).
The board at right interfaces with the radio button strip, which would probably be ousted for discrete switching in the event I get around to rehousing this unit too. This would be my candidate for pattern source.
They don't make them like that any more, who needs connectors interfacing between the circuits anyway?
And who needs a backing band when they can use one of these? The Band Box. I like this enclosure framework a lot, too bad they wrapped it in cardboard. Potential remains..
My contemplative abilities have sort of abandoned me on this one. I don't see a multi-pattern sequencer and sound source here, so logically I'm leaning toward this being a pattern sequencer. That said, as I recall organs operate via a bank of manually operated switches passing oscillator output, and being that there was not a bank of relays a simple sequencer would meet with difficulty tapping into the oscillator banks (which so far as I know do not respond to CV for instruction). When I was tearing this one down I was in more of an "I need some space" instead of an "I wonder how this works" frame of mind, more's the pity.
A heap of RCA transistors in a (presumably) functional black box. There, I feel better.