Tech equipment and a dummy load?

[Mark]

If someone asked me what equipment should be in a workshop to do amp repairs, I'd say, good multimeter, a signal generator, a CRO, and a dummy load. Most of this sort of thing is commercially available with the exception of the dummy load (though Weber's loads are a good alternative).

The issue is if you're testing an SVT (between 300 & 400 watts) there isn't anything out there. The next question is materials, do you use the aluminium clad resistors with heatsinks, of regular wire wound resistors?

A line out to hear the amp at comfortable levels is a plus too.

Aiken has a few good options too.

http://www.aikenamps.com/images/Documents/DummyLoad.pdf

What are your thoughts on building a dummy load?

[sluckey]

I like simple. This one cost me $10 and it does 4/8/16Ω just by changing a jumper.

[martin manning]

Here's mine. Enclosure is a 2.5 x 9.5 x 5 Bud box, the width of which is just right for mounting the load resistor at it's ends on hardware store springs. Sharpie pen graphics need a refresh now and then :^)

[Merlinb]

Here's mine. Only 60W rated, but I can push it well beyond that if the test only lasts a few seconds. One knob selects the impedance, the other is a line out control. It's made from a bit of aluminium I found in a skip, bent around and bolted to the heatsink.
[img:600:800]http://i81.photobucket.com/albums/j207/ ... c34669.jpg[/img]

At the last place I worked we had a 1kW dummy load, which was made from a slew of 0.1R resistors in TO-247 packages, bolted to a massive heatsink.

[Mark]

Thanks for the pictures and suggestions, they are all very helpful. I have one questions, how do you determine the size of the heatsink required on those aluminum clad resistors?

This has stopped me going in that direction as I've failed to see a spec or recommendation quoted.

Thanks again for all your assistance.

[martin manning]

This data sheet gives heat sink area and thickness for full rated wattage. http://www.arcolresistors.com/wp-conten ... -12.31.pdf

[Mark]

This is handy too.

http://docs-asia.electrocomponents.com/ ... 0b9f2b.pdf

I'm still finding it hard to find a heatsink. A CPU sink is dead easy but.......

[Mescalero]

For the occasional extended extreme (i.e.: full rated load power for more than just a few seconds) test I have placed dummy loads, heat sink and all, in distilled or DI water. However, there is a limit to how much heat the load itself can tolerate due to the thermal resistance between the actual conductive element and the package/heat sink/air. Bear in mind that extruded aluminum heat sink-housed resistors can essentially be "shot" forcefully out of the housing when they are dramatically overpowered. This can actually cause some significant collateral damage. Been there, got the tee shirt. Safety glasses are a reasonable precaution.

In a triode, no one can hear you screen..

[Mark]

Thanks for your reply.

I've done the water thing and it is funny to watch the load heat the water up and see steam come off it. I'm looking for a conservative heatsink which will be able to handle an SVT without too much worry.

[Merlinb]

You may find it easier simply to make your own heatsink from a big lump of aluminium or copper...

[cbass]

Anyone ever try using a stove or a hot water heater element for a dummy load?
or am i just being a dummy?

[Teleguy61]

Anyone ever try using a stove or a hot water heater element for a dummy load?
or am i just being a dummy?

Electric clothes dryer elements have been used, couldn't find the post.
Sorry.

[cbass]

Guess Ill try it Water heater element is 12.6 ohms
Stove is 6.7
the price is right

Itd be real easy to make a can of oil that the heater element could thread into. Id imagine you could run a huge amp like that

[darryl_h]

Mark, these resistors are available in 4Ω and 8Ω, @ 50W and 100W, from WES Components in Ashfield.

http://www.wagneronline.com.au/family.a ... UMMY_LOADS

[img:512:273]http://www.wagneronline.com.au/prodimag ... s/50W4.JPG[/img]

If you have a trade account there, the 50 watt resistors are about $7 and the 100 watt resistors are about $13 each.

[Teleguy61]

Guess Ill try it Water heater element is 12.6 ohms
Stove is 6.7
the price is right

Itd be real easy to make a can of oil that the heater element could thread into. Id imagine you could run a huge amp like that

I don't know, why not leave it in the water heater?
It would be double dipping-get your water heated while practicing.
I can hear it now--"Honey, could you go practice some more of that Hendrix stuff, the hot water's not quite warm enough for my shower."