This was how this story starts, as far as I am concerned. I was aware of the Maestrovox because of prior research into vintage tube keyboards, so when I saw this one linked from Matrixsynth I had to investigate. I bought it. Shipping cost more than the unit did!

And no, it did not work.

In the keyboard itself, this is the oscillator sub-chassis that carries the tubes V1 and V2. Part numbers correspond to the circuit diagram on the Maestrovox Official Website.


Again, all components and sleeved wiring needed replacing.


This sub-chassis is very hard to access, as the bottom rear corner has a hole through it, through which a shielded cable passes. I filed away the sub-chassis so I could free the cable from it. Along the rear edge, the sub-chassis has been hacked away, at the factory, to allow it to fit without hitting the keyboard resistor string.


These are  the Low and Medium octave oscillator capacitors. The rectangles are 1% capacitors, while the cylinders are compression trimmers. There is also one of this sort of capacitor directly on the rear of the octave select rotary switch. All three of these capacitors will need to be replaced. Two of them have already failed, reading around 5k6 on the resistance range of a multimeter.

In the keyboard itself, this is the tagstrip with the majority of components on it. Part numbers correspond to the circuit diagram on the Maestrovox Official Website.

Most of these components will need to be replaced due to them failing or going well out of specification with age. Some of the wiring is ratty, and in a few places, old rubber power flex has been used. Again, the sleeving used around tinned copper wire links had degraded to a sticky mess and will need replacing.

The sub-chassis to which the two tubes, V1 and V2, are mounted is bolted down. Circuit earth is through a lug sandwiched between it and the case, rather than by a wire to an appropriate tag.