5 Watt Wirewound Rheostat Potentiometer Variable Resistor

5 Watt Wirewound Rheostat, Potentiometer, Variable Resistor, Pot Various Values, Loudspeaker Volume Control

This is one item of new 5W wirewound pot as shown, available in various different resistance value variations. The taper is linear. The track tolerance is 20%.

The 25R picture shows the 25 Ohm version where 25 Ohms is represented by the 25 in the 026TB32R25B1A11217ZCTS engraving, that being being two, five and zero multiplier. The spindle is a standard round 6.3mm / 0.25 inch type.

The 25K version is probably not wirewound. You could conceivably connect this across a 300V valve radio H.T. supply to create a wide range variable bias voltage without exceeding the power rating.

Other applications about which I've been informed:

Airbag testing, 25 Ohm version (no further information)
Difalco slot car controllers, 10 and 25 Ohm versions are brake pots. (no further information)
Low power dashboard light dimmer (see below)
Low power loudspeaker volume and balance controls (see below)

More Application Information:

Loudspeaker Volume Control / Balance Control

I've seen the 25R version used as a loudspeaker balance control in a 1977 Land Rover where the output from a mono Blaupunkt car radio was sent to the wiper and either end of the pot to the 8 Ohm loudspeakers in the front and the rear, with the other side of each loudspeaker being returned to the remaining common loudspeaker terminal at the radio. This might have a similar application in a boat or caravan, but you need to be careful with the Watts and while it can be quite effective it's not terribly efficient. An old car radio giving typically 3 Watts maximum into 8 ohm speakers is about the limit for that system with these pots.

Dashboard Dimmer

In many older cars you will find the filament lamps in the dashboard illumination supplied by a variable resistor for night driving. Sometimes this is hidden away in a quite subtle place. This will often have been burned out and will only work when set to maximum. Why? Because the dimmer also supplies power to the dial illumination lamp in the old radio connector. When a new radio is fitted with non-factory standard connections, this low current dashboard lamp supply is often mistaken for the main radio supply. The heavy main radio load thus connected burns out the rheostat. If, and only if, the total maximum current for the dashboard lamps is less than 0.4A, you can use the 50 Ohm version of this to replace the hard-to-find dashboard dimmer rheostat. Just connect the middle and clockwise terminals in place of the old dimmer resistor. On a 1992 Peugeot 205 this is down to the left of the steering column fitted into the lightweight plastic cover.

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