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Rheostat 101

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Brosky

Brosky

Great Pumpkin
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Ever wonder what's really inside that switch that doesn't seem to do anything for your lights in the center of your TR6 dash? Well, here you are in living color.

The first post is the disassembly and the next will be cleaned and back together.

I had to grind off the hold down tabs and then the back just pops off. There was a good bit of crud on the contacts as well as the front and rear plates. Some contact cleaner and Never Dull took care of the tarnished copper and silver.
 
The first three show the crud on the inside and # 4 is everything all cleaned before assembly. Here it is cleaned up and glued back together with JB Weld. I did clean up the housing as well, but no pics until the weld is dry tomorrow.

This is the first stage of getting ready to pull the dash in the spring and install my new wood, along with cleaned gauges that I can hopefully make a little brighter by doing this and adding the 8 watt bulbs.
 
Looks like Egyptian tomb art inside that thing. Glad you did it, I just bypassed mine. A lot easier.
 
Jeff,

I talked to a guy at the Cape Cod Fall Show last year and he ran them all summer in his TR6 with no problems. I have some spare gauges that I'm going to clean up and test. I will install the bulbs in those and hook them to my 12V power supply and let them on for a few hours to see just how hot they get on the bench before putting everything back together.

Bill, I was thinking the same thing. More along the lines of the space ship that landed in the last year of the X-Files.
 
Oh yes, Tom. Here it is, awaiting gauges and warm weather.
 
Paul, thank you for these photos. My rheostat is toast, and you've inspired me to try to repair it. What weird innards!
 
Beautiful piece of wood. Something like that on a gun stock would be big bucks. Is that solid wood or veneer?
 
Paul - that dash panel is fantastic. Beautiful wood and beautiful finish.

Bravo!
Tom
 
Thanks guys,

It's a veneer and the pictures don't do it justice. You can see the grain and colors clearly from 10 feet a way. I got very lucky on ebay and as it turned out, the guy who made this one timer is here in MA, only about 40 miles away.

His main business is Jag & Healey dashes and wood and he did this and a TR4 dash as an experiment to see if he would want to mass produce them.

https://www.austinhealeywood.com/wood.html
 
Brosky said:
the guy who made this one timer is here in MA, only about 40 miles away.

His main business is Jag & Healey dashes and wood and he did this and a TR4 dash as an experiment to see if he would want to mass produce them.
Click to expand...

So if that is a 'one-timer', was his answer 'no' for mass producing Triumph dashes?
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] My rheostat is toast, and you've inspired me to try to repair it.[/QUOTE]

BC,

You will probably find a corrosion build up across the plates that won't allow current to flow. Be careful with the contacts. They're not dainty, but are copper, nonetheless.

This was a $10 ebay switch that I bought so I could learn how to rebuild it, rather than make a mistake with mine.

I may add power to it and test it with the 8 watt bulbs to see how hot it gets as well. I will need to find some sockets to fit the gauges to do so. Rheostats do build up heat and that is their biggest enemy.

Oh well, back to ebay to scrounge up a dash harness for parts.

Hey Dale, do you have any lamp sockets left from your harness swap? I can return them after the testing of the bilbs.
 
Shawn,

He said he was interested in making more as soon as he completes a big order from his main Jag customer for many wooden dash parts.

I think that the TR4 dash was the same gloss, but in black walnut.

I may ask him if I could visit him and take some pictures of his operation. Maybe I could get a field day for the Cape Cod Club organized if he's willing to show his place off. Some guys aren't willing to do that and some are.
 
I'd always assumed that rheostat was a wirewound device. I wonder why they used an etched board?
 
Brosky said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
Hey Dale, do you have any lamp sockets left from your harness swap? I can return them after the testing of the bilbs.
Click to expand...
Paul, if Dale doesn't come thru I still have 90% of my old wiring.
 
Earlier cars (like the TR3A) were wire-wound.

But to get what appears to be a linear dimming effect, the resistance needs to be logarithmic. Not sure, but I'd guess that's why they went to the thick film thing. If you follow the trace, it gets much longer and thinner as you go around the dial; meaning a larger change in resistance between each pair of pads.
 
A wire wound rheostat can be wound in either linear or logarithmic fashion, to make them linear, they just need a variable density, or more likely then core used to wind the resistance wire on varies in diameter. In the old days when audio components were all linear inside, good quality audio equipment used wire wound rheostats, and audio for similar reasons (response) normally use logarithmic rheostats.
Most likely they went to an etched PCB type to reduce costs. Good wire wound rheostats are expensive to manufacture. PCB type stats are cheap.
 
Thoroughly Modern Millie. Lot smaller in size. Unlike the heater rheostat which has to pull more amps.
 
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