Lionel # 8600 made in 1976 sound board variable rehostats.

[RDG-GEEP7]

I have a Lionel 8600 steam engine with the mighty sound of steam board in the tender. The chuff sound works correctly at very slow speeds, but when I speed it up slightly,  the sound becomes just a loud hissing noise. There are 2 adjustable rehostats on the sound board,would they be there to clip the sound between chuffs? If so how do you suggest that I correct this? Thanks.

[sir james I]

Check to see if the smoke pump is sticking. The chuff is made by a contact on the pump.

[ADCX Rob]

RDG-GEEP7

...There are 2 adjustable rehostats on the sound board,would they be there to clip the sound between chuffs?

Those are potentiometers, not rheostats.

The chuff should be adjustable with a screw at the smoke unit that sets the duty cycle of the copper leaf spring contact.

[lionelsoni]

The difference between a rheostat and a potentiometer is subtle.  A rheostat is simply a variable resistor.  (So "variable rheostat" is redundant.)  Charles Wheatstone, who invented it, built his from two cylinders, one metal and the other wood, with a resistance wire that unwound from one cylinder and wound onto the other as the cylinders were rotated by a crank.  So there was only one resistance ever in the circuit, that is, the portion of the wire on the wooden cylinder.

He also built a version that could have been used as a potentiometer.  It had a wiper that moved along a resistance-wire coil, just like a Lionel rheostat.  That one could have been used as a potentiometer simply by including both ends of the resistance wire into the circuit.

When a rheostat is built this way, the extra cost or effort to add that third terminal is so small that almost all variable resistances are actually implemented as potentiometers.  Sometimes the circuit in which the potentiometer is used as a rheostat connects the wiper directly to one end of the potentiometer, to limit the maximum rheostat resistance to something finite if the wiper should lose contact with the resistance wire or material.

The Tech Model Railroad Club used potentiometers to control the speed of HO trains (at least in my day).  Even though the voltage regulation of a potentiometer in an application like that is rather poor, the potentiometer had the advantage that the track voltage could be adjusted all the way to zero with no discontinuity.  The extra power wasted by the potentiometer in operating this way was not a concern--the club used far more power just to operate the "system" that kept track of the trains.