Raj Musicals Deluxe Dhruva Drone Synth

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via this auction

A video of one recently went up here.

"This is a rare Indian audio synth. It produces sounds similar to a harmonium, with a primary oscillator and two harmonizing oscillators that can be switched on or off.

There is a main volume control, as well as coarse and fine tuning for all three oscillators. It is powered with attached power cord or C batteries.."

Update via Loscha in the comments: "These are actually from the 90s, although they surely do look 60s.

I contacted Radel Saraang for information about these devices,and they no longer had the schematic, but, confirmed manufacturing time frame."