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andrewe1 30th May 2004 11:16 AM

8 ohm dummy load
 
Hi everyone,
just wondering if anyone out there knows how to build a simple dummy load for testing out amps?
I accured a valve test tone generator recently and wish to complete my testing equipment range, without resorting to blowing up amps in the testing process.
The dummy load must be able to take 8 ohms.
Thanks heaps
andrewe1

pinkmouse 30th May 2004 11:46 AM

For low power, a 20W 8Ohm wirewound resistor is fine, if you need more than that, just make up a network until you get the power dissipation you need.

SY 30th May 2004 04:05 PM

Quote:

For low power, a 20W 8Ohm wirewound resistor is fine
Non-inductive is best.

SkinnyBoy 30th May 2004 04:08 PM

nichrome wire... :D and water... lol or maybe oil... as it boils at a higher temperature... :)

pinkmouse 30th May 2004 04:46 PM

Quote:

Originally posted by SY


Non-inductive is best.

Probably, yes.

I just have a deep down feeling that a bit of induction more closely approaches a real load, ( even though it's nothing like the real thing)....;)

Nisbeth 30th May 2004 05:44 PM

7 pcs. 56 Ohm power resistors in parallel. Available up to 15-20 Watts each. Bolt to a heat sink for extra dissipation :)


/U.

Sch3mat1c 30th May 2004 09:10 PM

I have a monster 200 or 300W wire, or actually corrugated strip, wound vireous enameled resistor with sliding contact. I set it around 8 ohms (ohmmeter is a necessity) and blast away. Note that power capacity divides along the length, since if you're using half of it, only half is able to dissipate heat... so I've only got like 8 ohms 120W. Still more than I'll ever need. Until I use those 4CX250Rs. :devily:

As far as inductance goes, I don't know if that's what's causing the slight rise around 500kHz I usually observe while testing, but dammed if I care about a rise of 2dB when it's already down 40dB and at a frequency higher than the amp can respond to anyway. :D

Tim

Magura 30th May 2004 09:25 PM

Ive bought a bunch of 100W thick film resistors in TO-247 housing...mounted on a heatsink from the junk box it works very well. Its close to 100% non inductive. I think Dhaen bought a few of them from me a while ago to use them as dummy loads as well.

Magura:)

Centauri 31st May 2004 09:59 AM

WES Components in Ashfield, Sydney have 50W and 100W non-inductive resistors for just this purpose. Web : http://www.wescomponents.com/

I have 8x 100W units in a series-parallel network for high powered amps (got to fan cool them, though!).

Cheers

andrewe1 31st May 2004 10:00 AM

Thanks all
 
;) Thanks all who replied to my question. This has given me some good ideas. I found that you can buy an off the shelf dummy load for about $100 au which I think is a rip off when you can make one for a lot cheaper than that.
Thanks again
andrewe1


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