Older machines typically had a 850- or 1140-revolution-per-minute motor geared to the main clutch wheel, the inner shaft engaging this wheel while the casting cycle was in operation. An external leather belt on this wheel ran a second jackshaft, which powered the distributor and keyboard matrix conveyor and escapements through additional belting off this shaft. Gas fired pots, such as in the illustration below, were most common in the earlier years, with the pot being thermostatically controlled (high flame when under temperature and low flame when up to temperature), and then a second smaller burner for the mouth and throat heating, with the more modern installations running on 1500 watt electric pots with an initially rheostat controlled mouth and throat heaters (several hundred watts on the electric models). The temperature was precisely adjusted to keep the lead and tin type metal liquified just prior to being cast. Newer machines, and the larger machines above 36 EM Matrix size typically used the more standardized motor after v-belts came into common use in the 1930s. The large machines also had the so-called 'double pot', with either larger gas burners, or else 2250-watt pot heaters and larger mouth and throat heaters. The most modern Linotypes had the mouth and throat heaters thermostatically controlled, an improvement over the manual rheostat adjustment, or gas flame adjustment.