Dummy load... build or buy?

NoSoup4you22

NoSoup4you22

Keep on blorpin'
Feb 16, 2010
340
0
16
Minnesota, USA
www.myspace.com
Alright, so I've read and re-read the entire sticky thread here: http://www.ultimatemetal.com/forum/equipment/428323-home-made-dummy-load-tutorial-save-money.html

But there's so much conflicting information. Is it true that the method in the OP will ruin the amp? And if so, isn't it dangerous to have that stickied? :err:

On the other hand I'm a cheapass musician, and if there's a method in there that won't have consequences, I'm all for it. Either way I really need a dummy load because I keep waking up at like 8pm and being unable to record. FML

This is the resistor I was gonna buy: http://www.tube-town.net/ttstore/pr...ochlastwiderstand-8R2--8-Ohm----150-Watt.html

I'm wondering about the 8.2 ohms though, as I've heard tube amps need the exact impedance or lower.

Sorry about another thread on the subject, but I dunno if anyone's looking at the other one still...

EDIT: Alternately, I might just pick up a Tube Cube. Not a whole lot of information out there on it though.
 
Hey man, I'm glad you went through the whole thread... And yes, the whole OP is incorrect and dangerous. I'm also glad you're cautious and seeking a definitive answer on the subject.
Well, I can assure you that the most of the guys that clearly explained differences between serial and parallel wiring of resistors are correct, and here's the simple summary with the example of resistors with impedance of 8Ohm and 150W:

- SERIAL: If you put 2 resistors one after another you will get = 16Ohm and 300W (in this method both impedance and wattage are added to the sum)
- PARALEL: If you put 2 resistors next to each other and split the incoming signal to both of them you will get = 4Ohm and 300W (in this method impedance is divided by number of resistors, but wattage is always added)

Personally, I also bought two resistor from Tubetown instead of one - Why? Because the rating of the resistor you posted is 150W max, and 55W without heatsink (any kind of passive cooling will do fine, which basically means that you can get a decent box from electronics store that has heatsink "fins" on it like this one: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=262-070, or anything similar, really). But, to get back on the subject, it's generally better to have some headroom wattage-wise.

I personally bought two resistors of 16Ohm and 150W and wired them in parallel, so I have loadbox of 8Ohm and 300W...

Hope that helps... Good luck! ;)
 
Yes the OP is horribly incorrect, however myself and a couple other fellow EE's came in and made huge contributions to that thread.

The exact circuit is up to you, they make 300w 16 ohm resistors so you would only need one, if you want to get a few more of lower wattage, you will have to get the correct ratings and wire then up correctly, which is not hard at all (there are pictures on the DIY dummyload thread that are great examples of what it correct).

In terms of exact impedance matching, you don't have to worry about it, an 8.2 ohm resistor will work absolutely fine. Its actually slightly higher readings are slightly better as the amp will over-dissipate if you have a load less than what the amp was designed for. It would be a very slight over dissipation and would not damage the amp but might take a couple weeks off the lifespan of the tubes. You only see adverse effects if you plugged a 4 ohm load into a 16 ohm amp or used some stupid high load like >1K. By design tube amps are pretty tolerant on loads. You have to remember that the impedance of a speaker varies dramatically with frequencies and in some locations can have an impedance of 100+ ohms and have less than 8 ohms in some spots for a 16 ohm speaker. The impedance is usually measured at the 400Hz point.
 
Yeah disregard that thread. The best way is a SINGLE resistor rated for what you need. A 150w resistor in the required ohm rating is usually ~$30US. Attach your input jack to the resistor and you are ready to rock, essentially. Weber actually used to sell one that was perfect for this but last time I checked it's no longer available from them.
 
Is a 150w resistor good enough for my 5150? I keep the master volume at around 4 when recording. I had a good bid on a Tube Cube but now the price has gone up, so it's looking like this is the best route.

And if I do build this thing... How will I know if it's working or not? Maybe I'll test it with my crappy solid state head and see if it gets hot lol.
 
NoSoup4you22 said:
Is a 150w resistor good enough for my 5150? I keep the master volume at around 4 when recording. I had a good bid on a Tube Cube but now the price has gone up, so it's looking like this is the best route.

And if I do build this thing... How will I know if it's working or not? Maybe I'll test it with my crappy solid state head and see if it gets hot lol.
Click to expand...

If you don't crank it (and, really, you won't have to) 150W will be fine, but just be sure to have a good heatsink (decent box with cooling fins as I've explained earlier... and you'll be attaching the resistor to the interior side that has fins on it). If a 5150 has the same output options as 6505 then you'll be recording the signal out of the "Preamp Out", right? In that case, you really don't need to crank it past 3 or 4, because "Post Gain" doesn't have any effect on sound coming from "Preamp Out"... it would just make your resistor significantly (and unnecessarily) hotter.

To test the it just run it at moderate gain and see if gets hot...

BTW, you know you'll have to use speaker and not mic cable for wiring?
 
So if I wanted to build a dummy load for my 6505 would this input jack work? [ame="http://www.amazon.com/Switchcraft-Mono-2-Conductor-Input-Circuit/dp/B0049BKIF8/ref=pd_sim_sbs_MI2"]Switchcraft Mono 2 Conductor Input Circuit[/ame]

I would connect this to the resistor (8 ohm, 200W) with speaker wire and house it in a cooled enclosure, correct?

I just want to make sure I have everything correct as I have never done anything like this before.
 
ALivingSight said:
So if I wanted to build a dummy load for my 6505 would this input jack work? Switchcraft Mono 2 Conductor Input Circuit

I would connect this to the resistor (8 ohm, 200W) with speaker wire and house it in a cooled enclosure, correct?

I just want to make sure I have everything correct as I have never done anything like this before.
Click to expand...

Yup, you're good to go... Good luck! ;)
 
You must log in or register to reply here.

Similar threads

Djabthrash
Loadbox w. real loudspeaker drivers : Tube-Town Tone-Hound 8 Ohm / 100 W
Replies
54
Views
10K
Backline
TRUIE
T
Top Bottom
Back