Hammond Solovox -1940 - 1948

Circuit Overview:
     Solovox is a take off on the design of the Novachord to create a monophonic synth with preset buttons that can be accessed from below a miniature keyboard that is designed to be screwed in underneath a piano! Pretty much vacuum tubes, resistors and capacitors and transformers in these things. Oh and a huge inductor for tuning on my model K :-). I worked on a later one that you change tuning capacitor for range inside keyboard..model L I think we had there. Much lighter also. Lost the huge relay can in the middle. 4 sections of tube dividers after oscillator and several filter options. The vibrato on the J and K versions was an electro mechanical oscillator. ie. a flat spring with a slug (ferromagnetic cylinder) attached to an end and a solenoid in the middle. When you initially turn the switch for power/volume on a little piece on that rotating unit pulls the spring back to 'jump start' the lfo basically. So if it ever fails restarted it and turn it on faster first. Anyway in this position a switch is open but as it's relaxed a switch is closed that energizes the solenoid and pulls the spring back eventually to where the switch opens again and back and forth it goes! As this happens the slug goes in and out of a coil that modulates the pitch by changing the inductance of that series part of the circuit.

Service Tips:
     CLean all tube sockets with deoxit D5 first off probably and a lot of capacitors likely are getting leaky. Replace the coupling capacitors for sure in older models. And electrolytics. Resistors tend to drift way high sometimes. For stable flip flop dividers there needs to be reasonable match on the 270K resistors. I had a lot measuring over 300K and replaced them and it started working nice again. THe old electro mechanical vibrato generators may need some tweaking and switch cleaning. I had a time getting my vibrato to where inside the can!! I'd pull it down and at any angle it'd start right up and work. Put it back in and..nada! IT TURNS OUT that I had positioned it under my minikorg at an angle that was within a tenth of a degree or something of not working. So I'd put the bottom plate on front screws first and the thing is still vibratoing. But then I'd put the rear screws in and pull the slop forward that tiny amount and it'd STOP! I finally remounted it and it's ok now. Check out this 1949 article for general repair tips.