Rheostat needed

Hi! I need to find a rheostat for my sons boyscout project... he needs a rheostat that will handle 25 ohms at 200 watts. If anyone knows anyone who has one and would like to donate it or sell it at a reasonable price please contact me.

Bill snipped-for-privacy@yahoo.com

Newark Electronics lists two 25 ohm 300 watt rheostats, by Ohmite or Vishay - they are about C$ 150... (You have a choice of 150 or 300 watts - no 200 watt ).

$150.00 ? Well I can't afford that...thats for sure...

Perhaps you could explain the project in more detail. There is usually more than one solution.

What is the project?

There are adjustable power resistors, where changing the resistance involves a clamp held to the middle of the resistor by a screw. 25 ohms at 225 watts is in the $25 ballpark.

An alternative for this sort of thing might be a bunch of automotive or home light sockets in parallel, and the "resistance" is set by screwing in or unscrewing different numbers/types of light bulbs. Bulbs are not perfect ohmic resistors but you'd be surprised how well this works. And especially for a boy scout type project the result is visually very impressive.

Tim.

If your project involves 60Hz AC, a variac would be much better. They can be inexpensive surplus, $10 US or so for an unmounted one.

Al

It's the kind of thing you can sometimes pick up as 'surplus'. Few ppl actually use them any more.

You should look on ebay.

Graham

I've made them out of radiator elements but they are little used these days.

Hi Boris, My son's project is a thing he calls a "Power Soak" He had the schematics for it donated by a company called Weber Electronics. They (Weber) call it an attenuator. It is to be placed between a guitar amplifier and it"s Speaker or speaker cabinet. It allows the guitarist to run the amplifier at it's "Sweet Spot" (somwhere near it's top end or at a place in its volume curve that would be too loud normally) and have it at a volume that is perfect for whatever atmosphere he happens to be in. Weber uses two different ways of achieving this one uses very large power resistors and a rheostat or the Rheostat and what they(Weber) call a speaker motor... I don't know if this helped at all but I hope so because I don't have money like $150.00 for one of these rheostats...I also wonder after some looking if a thing called an

Bill G. snipped-for-privacy@yahoo.com

explain the project in more detail. There is usually more

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If you are running the amp at 100 - 200 W continuous you are way past the 'sweet' spot!

Radio Shack : 8-Ohm Non-Inductive Resistor Model: 271-120 $2.29 ea.

Use this as a load and try Model: 271-265 25-Ohm 3-Watt Rheostat $3.99 ea. to connect to the speakers.

That's $6.30 per channel.

Hi, Bill. I'm not sure a power rheostat is the right way to approach your project, but there are a number of surplus parts that can do the job.

For instance, Surplus Sales of Nebraska has a 35 ohm, 300watt rheostat for $35 USD (their P/N (RWA) M22/11-0111). Not great, but it sure beats $150.

Good luck Chris