Vintage Synth (Hillwood C-1A) - identifying missing component

[tenka10]

I acquired a Hillwood C-1A synthesizer with a burnt circuit board with 3 empty holes where a part needs to go. I'd like to repair the board but I don't know what component to look for... Help?

I've had one person suggest it might be either a large pass transistor or a voltage regulator IC in TO-220 package.