Dummy loads

[Off-Beat]

So with a lot of YouTube videos I see a lot if not most amp techs use dummy loads to plug their amp into when servicing / repairing. At the minute I use an external speaker. I have been thinking of getting some dummy load resistors.

This may be a silly question but I am still a novice! Can the dummy load be damaged just like a speaker? For example if I had an old tranny amp on the bench that is firing out DCV at the output stage, this would normally blow the speaker, would it damage the dummy load?

Second question is does anyone recommend a certain type or brand?

[The Dude]

Prolonged DC may damage a dummy load. It's going to depend on how much current the amp produces and the wattage rating of the dummy load. The dummy load is not likely to burn up as quickly as a speaker coil presuming a reasonable wattage rating on the load. That said, always check the amp's output for DC before hooking up any load so further damage is not done to the amp. You are giving the output a current path whether speaker or dummy load.

[Off-Beat]

Yeah I learned that the hard way! Poor speaker...

Would u recommend anywhere online to get them?

[The Dude]

I must confess that I haven't shopped for dummy loads any time recently. I've had the same loads for decades. Mine are some giant Dale resistors mounted on a large aluminum sheet for heat sink. Hopefully someone else will chime in. What wattage load are you trying to achieve?

[Off-Beat]

I haven't even thought that far into it. I was just thinking it May be a good idea to get some rather than risking blowing another speaker.

[The Dude]

I'm not endorsing these, because I haven't used them, but the price is right. You could build series/parallel combinations if you need more wattage.

8 Ohm 100 Watt Resistor for Dummy Load 2pcs per Lot | eBay

[The Dude]

FWIW, I keep a few crappy speakers robbed from radios, boom boxes, or whatever around the shop to run "suspect" amps with for a while before I hook up the actual speaker(s). You can "keep an ear on it" while you work and you don't have to care if they blow up or not. If one smokes, I just toss it and find another one. They don't have to be anything special- just something that makes sound.

[Enzo]

And unless you are doing some sort of precision testing, close enough is close enough. For example finding surplus 4-8-16 ohm resistors is harder than finding 5 ohm and 10 ohm ones cheap. At Fair Radio I just saw 15 ohm 95 watt Dales for $1.75. Two of those in parallel gets you a 7.5 ohm 190 watt load. Close enough and cheap. A pair of loads for under $10.

https://www.fairradio.com/catalog.ph...ategoryid=4230

[Off-Beat]

Thanks guys that helps a lot. I know this type of stuff is usually easy to research online but I like to see what people with actual experience have to say. Plus anyone else who has the same question may benefit from the post.

[es345]

I know it looks like an overkill, but I was tired to look for the right load resistance with enough power margin.

Its a chain of switcheable 150W resistors (1Ohm, 0,5 Ohm) that I can set to any value up to 9,375 Ohm. The background is that for test purposes with this bank you can also vary the primary load of a tube amp and see what is the impact to the resulting output power.

[Off-Beat]

That's awesome! How much did it cost to build?

[Chuck H]

With the aluminum housed resistors, the 50W units are the best value ($ per W). At about $3.50 a piece for the Arcol brand at Mouser. Here's a load box I (re) designed that'll do 4/8/16 ohms at 200W and has a low level speaker output for audio monitoring if desired. I use a very similar load box (the first incarnation of this design).

Just screw the resistors to the top side (inside) of a Bud box or Hammond chassis. That way there's a place to put to put the impedance switch and the jacks. Add some rubber feet and Bob's your uncle.

[es345]

How much did it cost to build?

Its about 250 Euro including switches.
Each switch can shorten the related resistor. The load line is never open. So you can change the load under power.
But as I said: for standard application " a little bit too much".

[audiobrad]

Hi there , i use a simple 4 kettle elements , rated at 1500 watts per element and are 16 ohms each .So i have a 8 ohm 3000 watt or 4 ohm 6000 watt dummy load.The dummy load is working every day for two years now without any problems. i thought i would let you know there are other ways of making a dummy load without any major effort . COOL TREND !!!!

[Off-Beat]

Thanks!