Wirewound Resistors Dummy Load question

[Pryde]

Working on building my tools for amp repair and am looking at dummy load options

Mouser has various watt ratings for 4, 8, and 16 ohm WW resistors and was wondering what minimum wattage would I need for amp repairs

Is a 150 watt resistor enough, not enough, too much? Just buy 1 each of 4, 8, and 16 ohm 150 watt resistors and that's it? Thanks for the help.

Here is one example of an 8 ohm, 150w:
HS150 8R0 F Arcol | Mouser

[g1]

Depends on what is the highest power amp you will be testing. Guitar amps? SVT's? Solid state PA amps?

[Pryde]

Not sure but I guess I want to be equipped to do both SS and tube amps. What do you folks have in the shop in terms of dummy loads? (i.e. maximum watt values)

[Sowhat]

I do guitar and bass amps mostly, rarely anything above 400 watts. I ignore 2 ohms and 16 ohms simply because I have found no real utility for those values in building and repairing amps. Attached is my dummy load which consists of 4 16 ohm 100 watt resistors that I can switch in pairs giving me 8 ohms at 200 watts or 4 ohms at 400 watts. It also has a 1/4" audio jack as well as a Speakon jack for connecting stuff. All the wiring is naked 14ga buss wire so I can clip on meters, scopes and whatnot to do mad scientists things... bra-ha-ha-ha!



I find that having a stout heatsink like I have here is essential if you want to cook equipment for long periods of time at full output.

[Pryde]

I do guitar and bass amps mostly, rarely anything above 400 watts. I ignore 2 ohms and 16 ohms simply because I have found no real utility for those values in building and repairing amps. Attached is my dummy load which consists of 4 16 ohm 100 watt resistors that I can switch in pairs giving me 8 ohms at 200 watts or 4 ohms at 400 watts. It also has a 1/4" audio jack as well as a Speakon jack for connecting stuff. All the wiring is naked 14ga buss wire so I can clip on meters, scopes and whatnot to do mad scientists things... bra-ha-ha-ha!

[ATTACH=CONFIG]27299[/ATTACH]

I find that having a stout heatsink like I have here is essential if you want to cook equipment for long periods of time at full output.

Cool rig! So then are you only to do 100 watts with a 16 ohm load if you need that?

Have a diagram of how your rig is setup/wired with the switches and connectors?

[Sowhat]

It's a pretty straight forward thing...



I suppose you could add another switch in the line and get 16 ohms @ 100 watts, 8 ohms @ 200 watts and 4 ohms @ 400 watts but I have never run across an amp that only had a 16 ohm output tap. Everything always has at least an 8 ohm tap and amps that have a 2 ohm tap always have a 4 ohm tap as well minimum. I find that 4 and 8 ohms float my boat just fine and I've been doing this stuff since Johnson was president. The big thing here is not the circuit but the physical construction. Those Arcol resistors are not meant to be operated just sitting there, they need a heat sink, and a pretty massive one at that. If you shove 100 watts into one of those without a smooth, even heat sink firmly attached with thermal grease an tightly torqued screws it will melt down guaranteed... read the spec sheet on them.

[Enzo]

I like the nice aluminum Dale - or similar - power resistors. I have a bunch of the 250w ones here, from before they cost more than my car.


You can combine them, as Sowhat did. I looked in Mouser at 100w 8 ohm Arcol aluminum ones, they were $12.22 each. The 50w 8 ohm Arcols were $4.27. So two 50w resistors cost a lot less than one 100w resistor.

[Mick Bailey]

Here's my setup; It's wired as 4x4 ohm sections and I use banana plugs to configure it for different loads. It's useful when working on stereo amps so I can load both channels at the same time. I can then get 2,4,8 ohms per channel. The fans keep it barely warm when testing high output gear.

[nashvillebill]

Here's mine. I used 8 of the Parts Express dummy loads. There's a muffin fan underneath when I need to do high-power stuff. I can switch out half of the bank and drive that half separately, if I want to test a stereo amp with both channels driven. The meter is a RF ammeter, must be 60 years old, it added a cool touch. I can switch the ammeter in or out or use an external ammeter as well. (Using the ammeter and a voltmeter, I can just multiply V times I to get Power...)

[Jazz P Bass]

Nice loadbank, NB!

You are fully prepared to test QSC amps.

[Pryde]

Good stuff everyone. Love to see the unique ways people setup tools in the shop.

I believe I will build up a rig similar to Sowhat above using 4 100w 16-Ohm Arcol resistors. Just a few clarifications:

-As far as connections is the 1/4" jack and the SpeakON sufficient? I haven't used a speakon but the idea is that it will accept adapters for different types of connections?

-is that a piece of billet aluminum for the heatsink? What should I use and were to source?

-Is the toggle switch a SPDT carling or similar?

THanks

Also

[Sowhat]

Good stuff everyone. Love to see the unique ways people setup tools in the shop.

I believe I will build up a rig similar to Sowhat above using 4 100w 16-Ohm Arcol resistors. Just a few clarifications:

-As far as connections is the 1/4" jack and the SpeakON sufficient? I haven't used a speakon but the idea is that it will accept adapters for different types of connections?

-is that a piece of billet aluminum for the heatsink? What should I use and were to source?

-Is the toggle switch a SPDT carling or similar?

THanks

Also

My parts list is something like this:

Carling SPST switch from Mouser: 691-CA201-73. Any nice 250 Volt switch will do, I use this Carling one because it's a small package and I have a tight space to put it in.

A Neutrik NL4MP Speakon connector. It's a stereo model because that's all the local store had. I just didn't wire up the second circuit. The 1/4" jack is a switchcraft L11 type which I had laying around the shop.

Those 4 Arcol 16 ohm 100 watt resistors I got from Mouser a long time ago, I forget the part number but I think you know what and where on those.

The aluminum stuff is from McMaster-Carr (mcmaster.com), I used:
8975K415 Multipurpose 6061 Aluminum, 1/2" Thick, 3" Width, 1' Length
6546K221 Multipurpose 6061 Aluminum Rectangular Tube, 1/8" Wall Thickness, 1-1/2" x 1-1/2", 1' Length

One last little tidbit from Mouser is 4 Keystone 3/4" x 10-32 Phenolic Standoffs: PN 534-470 to mount the thing to my wood cradle. You need some sort of thermal isolation from the wood to keep it from charring, phenolic works good for that.

I used some pilot drills .120 and .175 for the 6-32 and 10-32 machine screws and the corresponding taps, a 1/2" and 3/8" drill for the big holes, a hack saw, dremel tool with cutoff blade, some sandpaper, a file to hack out the parts. Everything is fastened together with 6-32 X 3/8" socket head cap screws and the standoff assemblies are using those standoffs, some 10-32 threaded rod and 4 10-32 X 1 hex head bolts.

All that plus some 14ga buss and jacketed stranded wire, a little heat shrink and you got it.

Oh yeah... the Speakon is the high power connector you find on most new higher power bass amps. It's rated for 30 amps. Amps over 250 watts usually have those now a days. I would imagine Hi-Fi guys would benefit from some banana connectors but for musical instrument amps those are not really used. Make 2 of these and you can handle stereo equipment but I find that having just one works good for me, even with biamps like some of that David Eden stuff. You don't really need a dummy load for Solid State amps but it's nice to have in order to do wattage measurements or load testing without scaring the neighbors.

[g1]

(sorry, g-one, my mistake)

[Enzo]

g-one, a big apology. I went to post a reply and inadvertently edited your post instead. I found my message in your box. I couldn;t recover your post then.


You mentioned bananas as a good idea, and i agree. I use my banana posts more on my patch board than the other connectors. Many combo amp chassis have bare wires and my banana to clip patch cords are perfect for it.

[Pryde]

g-one, a big apology. I went to post a reply and inadvertently edited your post instead. I found my message in your box. I couldn;t recover your post then.


You mentioned bananas as a good idea, and i agree. I use my banana posts more on my patch board than the other connectors. Many combo amp chassis have bare wires and my banana to clip patch cords are perfect for it.

Will these fit the bill for the 5 way plugs: The data sheet doesn't give any specs on receiving "banana" plugs or anything. Am I looking at the wrong type of binding posts? I love Mouser but sifting for parts can be a pain sometimes.

7016 Keystone Electronics | Mouser