High wattage dummy load/s for audio use

Nigel,

To me 2.8 ohms is an odd value. I have DALE 8 ohm 250 watt, non inductive winding resistors. With four of them, I have 8 ohms at 250 watts, or 4 ohms at 500 watts. If I had felt the need I could have done some more complicated switching and also had 16 ohms at 500 watts.

They are very useful as you can hook them up as a dummy load and view on your scope, and run rather large amp right up to clipping, all while not having to listen to any of it. It also makes it easy to measure power at clipping, as long as you also monitor your mains voltage. (At clipping, you have to watch the voltage drop at your bench outlet, as you might be feeding the amp a lower mains voltage than it is specified for, which will reduce power output. I have a VARIAC to correct for this.)

I have seen one manufactured unit that used 7.87 ohm resistors, as they figured out the resistance of the wiring and switching. I put together my own, and did not feel the need for that level of accuracy.

The loads that I have are resistive, so not as difficult to drive as a speaker might be, but again, good enough for my needs.

You did not specify the make or model of the resistors, or how they were wired up.

Regards, Tim Schwartz Bristol Electronics

On Wed, 23 Jun 2010 08:48:22 +0100, N_Cook ??o??:

Most newer SS amps are rated to a minimum of 2 ohms.

from

with L

this.)

Marked neatly on the curve 2R8 +/-5 % and then 87.31 perhaps 31/52 of 1987. I picked up the last 3 at a hamfest on Sunday, I did not think to ask how many he had originally. I'd not googled the Arcol name stamped on the brackets as they did not look original to the resistor section, thinking it was just a maker of steel brackets. Crinkle form type at top of this image

And cheapie meter leads might account for the extra 0.8 Ohms?

On Thu, 24 Jun 2010 00:30:47 +1000, Grant ??o??:

They'd have to be very cheap. Mr. Kook is a talented technician so I think that we can rule out that factor.

I use a pair of finned 300 watt 8 ohm resistors mounted on a giant power supply heat sink to raise their continuous rating. Got them from Yamaha way back in the 80's when I did warranty work for their pro-audio line. They aren't branded Yamaha. They sent them to our warranty station along with some other equipment they required to authorize us. If I recall the total startup cost was a couple thousand bucks but we also had a credit line with their service/parts dept.

You'd need at least 90' of them (at 20 AWG)

or 8' of 30AWG, but I've never heard of such slim wire being used for probes.

CAR AMPS

I typically get .3 ohms on the Fluke.

I have a couple dummy loads. One with 8- 50 watt gold chassis resistors attached to sink with fan. I have four more separate sinks without fan. I either choose 8 ohms or 4.

greg

the ones I used were just large (hundreds of watts) ceramic wirewound resistor mounted in heatsinks. They had to have been 8 ohms or something really close as to not blow up 1970s and 1980s equipment.

you could hear the music though them if you got close enough.

My highest power dummy load is a (hacked) 3KW fan heater.

Gareth.

I got a cheapie with that much resistance, is why the number rang a bell. A cheapie no name meter that measures .8 or .9 ohm for short circuit with its skinny leads ;)

But, the OP mentioned upthread the 2.8ohm value was marked on the resistor, the size of his resistors are similar to some 5ohm 300W resistors I have here (Ohmite C300K5R0E).

Grant.