How to make a dummy load for amp testing

[ksrigg]

How do you make a dummy load for Phase Linear testing? ApexJr. has some 7.5 KOhms 225 watt resistors, some 25 Ohm 225 watt resistors, some 15 ohm 250 watts resistors, and some 100 ohm 200 watt resistors..

Could I build dummy loads using any of the above?

I'm guessing two of the 15 ohm 250 watters in paralell? That would produce a 7.5 ohm 500 watt load to the amp??? Think this would do it, or is there a source for true dummy loads which is equally affordable? You know me and the "cheap trash bag" description. I could make a PAIR of dummy loads for $30.00 using the Apex resistors. I think as long as it does what it is intended to do, why spend the extra money?

 

[Rex Everything]

Not sure if these will handle enough watts for you but this is the route I went

http://www.parts-express.com/wizards/se ... ad&x=0&y=0

 

[ksrigg]

Ild go for two per side to get to 400 watts, but I'm at $130.00 plus....really more than I would like to spend...it does show me that I should put the resistors inside some type case or box though....so I can warm my coffee as I test...

Thanks for the suggestion...

 

[Rex Everything]

NP...I have a pair of 100 watt 8 ohms for messing around with tube amps for fun........

 

[Skratch]

Sutton, you could use the 15 ohm in parallel and have a 500 watt 7.5 ohm which would be close enough. Or you could load the amp with 15 ohm 250 watt and it would be good for a 400 and figure the power from there.

 

[ksrigg]

I emailed Steve and he is out of the 250 ohm 250 watt resistors anyway, so problem solved for that lot anyway. He suggested some others, but for right now, if someone can basically tell me if resistors approximating the ohmage and wattage values of an amp WILL WORK as a dummy load, that would probably get me going in the right direction. I THINK I know the answer, but I'm not 100% sure. I THINK as long as the ohmage is 8 ohms OR HIGHER, and the wattage the resistor is rated to handle is equal to, or greater than the rated wattage of the amp...then I should be good to go. For safety, I would think putting the resistors in a box or some enclosure would be a plus in case the resistors do go BOOM...

DAMN IT .................................................................................................................................I just blew my other McIntosh MC2125....Gotta check the fuses, but I'll bet she has done the same thing as the other one...

Mark.........you're going to get TWO big heavy boxes sometime soon.....as soon as I can win the lottery or something...

 

[Skratch]

Sutton, Buy 4 of the 15 ohm 250 watt resistors and parallel 2 of the 15 ohm together and you will have a pair of 500 watt 7.5 ohm dummies. Mount them on a metal plate, prefer to use aluminum and you will be good for just about anything you can throw at it

 

[laatsch55]

And they do not blow up Sutton, just get real hot and smoke you out of the house. Dead burnt resistor smell is almost as bad as dead burnt mouse smell.

 

[orange]

My uncle did it by shorting his forearm against a Cantenna.

NOBODY TRY THIS AT HOME.

Fortunately he is in his 70s now

 

[ksrigg]

Steve at Apex is out of stock on a lot of these resistors. If I can find a combination of ones that will work...to get close to 8 ohms..

 

[NavLinear]

Ebay has a seller (from China) that lists 8 ohm 100 watt wire wound resistors (5%) for 6.99 each or 5 for $29.99 with free shipping. I'm not familiar with this seller but it's another alternative. I'm looking to build some loads so comments are appreicated.

http://www.ebay.com/itm/5pcs-8K-Ohm-100 ... 3a6b7b04d9

 

[Gepetto]

Those are 8K ohm, not 8 ohm Dennis. I am sure there are others out there though. Usually you can find some old Ohmite WW ones with that nice maroon color that Lee likes so much

 

[NavLinear]

Thanks Joe - I got excited over the five for 29.99. Ok how 'bout this:

http://www.ebay.com/itm/8-Ohm-8R-100W-W ... 25686e8ea5

 

[Gepetto]

There you go, correct value now, remember these have to be mounted to a hefty heatsink to get the 100W rating. These metal cased resistors are not power rated without sufficient heatsinks.

 

[laatsch55]

Ah, but they're not CDE maroon, so it's all good.

 

[NavLinear]

Well - it looks like my first set of dummy loads will be resistive. From what I've read in the PL 400 Service Manual the load it calls out for is resistive and should be capable of handling a minimum of 250 watts RMS.

What I'm thinking is four wire wound 8 ohm (5%) 100 watt resistors per channel - two parallel legs in series with each other with bananna plugs as the interface and a big a#s alumimum heat sink. As always inputs are appreciated.

Dennis

 

[ksrigg]

Sounds like what Skratch and I are doing..You'll need two sets of those though......one for each channel...of course..Lee, Joe, Skratch, Mark (Dr.) have all made these before, so they are more qualified to answer, but sounds right to me..

 

[laatsch55]

Dennis I had a bunch of 100 watt 2ohm Ohmites from a very large printer I scrapped, 4 in series was plenty even with no heatsinking, but now that were testing the WOPL's into 4 ohms, that's about half of what I need.

 

[ksrigg]

Here is the dummy load made for me by Skratch. They look awesome. To give you an idea of scale, each resistor is ten inches long and the finished product is one foot square. They represent a 8.5 ohm load and are capable of taking 675 wats PER CHANNEL, or over 1300 watts. Apex Jr. had the resistors at $3.95 each, os we have about $25.00 in the dummy load...plus shipping.... Just thought everyone would be interested in seeing this. It is simply too cool and sure as hell beats paying a couple hundred dollars for a factory made dummy load.

Thanks SKRATCH..

 

[speakerman1]

Cool

Larry