What would be the best way to put a load on an Amp w/o speak

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skullfxr

skullfxr

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Without a speaker. This would just be so I could diagnose / troubleshoot an amp while on.

Could I get four 4ohm 25 watt resistors and wire them in series/parallel and hook them up with a jack from the amp to the resistors. Wouldn't that essentially be 4 ohms capable of handling 100 watts for brief periods?

What should I use for a heat sink?

I work on old fender amps a lot ATM and would want a 4ohm load.

Is this a bad idea? I would not be pushing the amp hard, just checking components on a live amp
 
stephen sawall":1cjzrflt said:
I use a THD Hot Plate.
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Good to know.

The resistors are a hell of a lot cheaper if it would work. I don't need sound, just want to hold the load to read live values in the amp.
 
Get chassis-mount resistors and put 'em in a Hammond die cast aluminum box. The power of the resistors will add up if they are wired in series.

Reactive load boxes are good, but you need a purely resistive load to accurately measure power output. And they are cheap and easy to make.
 
V2a":1cb3fmmy said:
Get chassis-mount resistors and put 'em in a Hammond die cast aluminum box. The power of the resistors will add up if they are wired in series.

Reactive load boxes are good, but you need a purely resistive load to accurately measure power output. And they are cheap and easy to make.
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Thanks so I need 4 ohms, so four 1 ohm 25 watt resistors in series will do what I need? I can mount them on a pedal box. Any useful links?
 
panhead":3rsysqfe said:
100 watt speaker motor from weber
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Is that technically reactive or resistive? Which would do better for my use?
 
Not sure but it would be just like a speaker cause it is. I don't see them on their website any more. I put one in a 4/12 long time ago mounted inside on the floor of the cab. That way I had the load where ever I took the cab. 50 watt plexi/ direct box /lexicon/ return to a peavey 120 mono poweramp to cab with gb`s .
 
burger":26os38jr said:
I grabbed a 100w 8ohm resistor from eBay. Was cheap and works great. It gets very hot if cranking 100w of power through it continuously, but I find I only need it for a minute at a time to take power measurements on my scope.

Something like this:
https://www.ebay.com.au/itm/100W-8ohm-5 ... SwQOxdYJCd
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I may just do that. Did you mount it to an enclosure and heat sink it?
 
Usually, you make standoffs mounted to a piece of wood with the resistors up in the air a few inches so there is air movement around it/them. They get STUPID hot, so be careful ! For a reactive load, a good 100+ watt speaker (EVM 12L for example) with the cone cut out but a good voice coil works great, so if you find a used EV with a tear, rip, hole etc in the cone but the voice coil is ok you’re golden.
 
paulyc":3u1qq7vk said:
Usually, you make standoffs mounted to a piece of wood with the resistors up in the air a few inches so there is air movement around it/them. They get STUPID hot, so be careful ! For a reactive load, a good 100+ watt speaker (EVM 12L for example) with the cone cut out but a good voice coil works great, so if you find a used EV with a tear, rip, hole etc in the cone but the voice coil is ok you’re golden.
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Thanks for the solid advice. I am probably going to get a pair of 100W resistors and run them in parallel with a standoff. That way it would handle 200W and would displace the heat better.

I don't want a reactive load for the reason V2a said. I need to be able to get accurate readings.

But I will keep the idea of cutting out the cone in mind if I do.

This is just for tweaking circuits in amps. Not for a recording dummy load.
 
If you are intending to mute the amp input when you are measuring, then there will barely be any power at the output. It's not until the power amp starts working hard that any heat is generated in the output load. So if you're just intending to measure voltages with a muted input then you dont need the resistor to handle any power at all and it wont get warm - Just solder something to across a jack.
 
I spent $6 on Amazon for a pair of 8 ohm 100 watt resistors and will run them in parallel for 4 ohms and be set!

Thanks guys!
 
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