Gearing and heating
A little 12Vdc motor with internal 3000:1 gearing (MFA 3000:1, Conrad.nl orderNr: 222368) can be fed from a small power supply. The motor itself and its drive lines are floating from ground, and make the use of a simple automatic tuner possible.
A second reduction 10 tooth : 48 tooth, is made of aluminum tooth wheels and a rubber tooth belt. I used a belt without steel reinforcement to prevent flash-over. But later on i grounded the shaft of the split stator for loop balancing purposes. As it is now on ground potential, a steel enforced belt could be used. The big wheel needs an adapter for 6mm (shaft) to 16mm (tooth wheel). An extra ordered 10 tooth wheel is used here, and after removing its flanges it fits nicely.
The total reduction is adequate for use on the 80m band, especially when the motor voltage is adjustable between 3V and 12V. In my case, the remaining slag is only e few kHz on 80m.
The tuning capacitor is mounted onto an Trespa bracket. This can be sledded side wards to adjust the belt for minimal slag and tension.
On the motor side of the cabinet, a piece of Trespa is screwed to stiffen the side wall. Preventing bending and a not closing lid. The motor is mounted onto it. As the motor bracket is a bit thin, the back end of the motor is supported by gluing a little block between the motor body and the bracket.
A 12V / 5W heater (4x 120Ohm / 2W parallel) is on a double sided PCB, effectively prevents condensation in the cabinet. This PCB also contains the filtering of the motor- and power lines. All lines are electrically floating.