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Old 15th January 2005, 04:19 PM   #11
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I am using 5 - 40 ohm, 3%, 50 watt resistors in parallel. These are mounted on a sheet of PCB material -- and it really cooks. Over time the copper sheet has become "heat treated". I connected a piece of #12 wire onto the PCB material -- on which various clips can be attached (for the scope etc.). This also attaches to the amplifier ground.

Opening up the thread, however, I note that when you do the PDMax calculation for an amplifier it presupposes that you are using a resistive load, not the case in real life -- the transistors or opamps seem to bear more of the power dissipation than the load -- a little bit of trig comes into play for real life examples.

anyone up for some brainstorming a reactive load -- I think that Gary Galo has one in his book on testing loudspeakers, and seem to recall one on Marshall Leach's website ...
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Old 16th January 2005, 07:19 AM   #12
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I'm wondering if the answer might just be to use a big old voice coil from a pro woofer. You could put fan on it, or maybe dunk it in a can of oil for cooling purposes.
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Old 16th January 2005, 07:44 AM   #13
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I use 4x 16ohm 75W wirewound resistors I got at a surplus place for $1 each. 2 per channel with a switch to parallel them,16 ohms 75W or 8ohms 150W per channel.Or I can parallel both channels for a 300W 4ohm load (could add a second switch for that too.)
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Old 18th January 2005, 10:17 AM   #14
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I bought two of the 100W ones Centauri is talking about, from WES a couple of weeks ago. They are non-inductive and I think cost less than $20 each. So would be a lot cheaper than your $100 one.

Tony.

edit: you might want to check this thread I started a while back too
Resistors for dummy load?
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Old 18th January 2005, 10:19 AM   #15
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Quote:
Originally posted by pinkmouse
I'm wondering if the answer might just be to use a big old voice coil from a pro woofer. You could put fan on it, or maybe dunk it in a can of oil for cooling purposes.

My flat mate suggested something similar to that the other day, He said why don't you get some old speakers and rip out the cones, and then you will have a more realistic load ......... I wondered whether without the cone and surround, it would just shoot straight out of the gap

Tony.
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Old 18th January 2005, 03:14 PM   #16
markp is offline markp  United States
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I use two 16 ohm wirewound 300watt monsters in parallel wired with the spirals opposite each other to lower inductance. Its a big one!
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Old 18th January 2005, 03:46 PM   #17
Apex Jr is offline Apex Jr  United States
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For those of you who do need dummy loads I have in stock:

Dale RH 50 50 Watt 8 ohm alum housed resistors at $2.00ea

Ohmite 15 ohm 225W Ceramic 10 1/2" long resistors at $3.95ea

Series and Parallel will give you variations

Steve @ Apex Jr.
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Old 23rd January 2005, 04:16 AM   #18
Mr Teal is offline Mr Teal  Canada
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I have two of these, they're pricey, but if you bolt them onto an old heatsink and get some air moving over it, they can take ALOT of power.
http://www.partsexpress.com/pe/showd...number=019-030
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Old 23rd January 2005, 08:44 PM   #19
markp is offline markp  United States
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Quote:
Originally posted by Apex Jr
For those of you who do need dummy loads I have in stock:

Dale RH 50 50 Watt 8 ohm alum housed resistors at $2.00ea

Ohmite 15 ohm 225W Ceramic 10 1/2" long resistors at $3.95ea

Series and Parallel will give you variations

Steve @ Apex Jr.
I bough a few of those ohmite power resistors from the original Apex about 10 years ago and they are still used as dummy loads today. They also make great cheese graters!


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Old 27th January 2009, 09:07 PM   #20
amptech is offline amptech  Scotland
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Default dummy load idear

here's an high powered load for testing amps

I use two 10 ohm @200w each and three 1 ohms @200w wired for a 8 ohm load '1000w. or 10 ohm@300w each plus 1 ohm@300w each. total power 1200w nice

have fun
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