8 Ohm Load For Vacuum Tube Power Amplifiers

[@Technical_Audio]

Excellent idea! And it’s very useful that you tested for resistance changes with temperature and also that you measured the inductance (the value is given in the description). If a pair of these elements has a resistance of 8.0 ohms and a series inductive reactance of 0.79 ohms at 20KHz, then the magnitude of the complex impedance at 20KHz is 8.04 ohms, with a phase angle of 5.6 degrees, if I did my hasty math correctly. That’s not bad at all. Some might think that the combined impedance magnitude would be 8.79, but that would be wrong and doesn’t account for the vector summation of an inductance and a resistance. This magnitude of impedance of 8.04 ohms at 20KHz shows that the inductive component only raises the magnitude by about 1/2% at that frequency. This is more than accurate enough for most high-power testing.

[@guitfidle]

THANK YOU!!! I don't know why i never thought of that, I work for a coffee company, i run the refurbishing shop- i have a milk crate full of used heating elements. Thanks again!

[@1oldtexan922]

I love this dummy load. I built a 4 ohm version, 4 elements immersed in vegetable oil and I can run a 300 watt amp all day on it with no change in load.

[@UltraCon79]

You just showed me how to create a dummy load for my Rockford Fosgate! Nice!!!

[@fpliuzzi]

I like your implementation. Lowes will probably be wondering why these heating elements are selling so well all of a sudden. Nice video.

[@ElPasoTubeAmps]

If Lowes starts selling lots of them, the price may go up - maybe we should buy Lowes stock ... :-)

[@JesusvonNazaret]

nice dummy load, very interesting how that it doesn't change it's resistance with the increased temperature

[@fullwaverecked]

I found that very interesting as well. It somehow regulates with no regulator... Maybe sorcery?

[@RandyOnTheRadio]

Very cool idea. Randy, TLC.

[@TheBoss1597]

Talk about inspiration, Great!

[@bain5872]

Great Job. I've always used a dryer element because I've never had the need to dissipate that much power however, I have thought about using these hot water herater elements before and wondered how stable their resistance would be. Well sir, thanks to you, I now know. I was thinking that oil as a dissapent would finish off a perfect high wattage dummy load. Their's a lot of amp guru's that will be off to see the wizard at the wonerful land of Lowes. Kudos!

[@ElPasoTubeAmps]

Great - I am always pleased to post something that will help others. As for oil, I don't know how they will react as the oil will allow the elements to reach a much higher temperature than they are designed for - the water boiling will keep the temperature to 212 F or so, it might be a good idea to do some testing in oil - on the other hand, unless a person is seriously pumping a KW of power into them oil or water might not make any difference at all - I would love to know the outcome if you do any testing with oil. Thanks for your comments.

[@bain5872]

You got a point there.I really didn't think about that. The only concern I was addressing with the oil was long term life of the elements but on the oher hand though, these things run full power in some foul mineral rich water for years on end so I'll have to agree with your dicission for using water. Much better heat transfer. Again, great job and thanks for sharing.

[@ElPasoTubeAmps]

bain5872 You have a good point - these things live in a hostile environment for years caked in minerals - I guess they will do fine in pretty much any liquid that can dissipate the heat away from them. Oil certainly won't evaporate or boil off like water. I wonder what two gallons of mineral oil would cost - probably more than the entire dummy load :-) Maybe just strapping them to a large heat sink and putting a fan on them would be OK.

[@bain5872]

I agree with the price of the oil. I think H2O is the way to go here. Maybe a pint of antifreeze would keep the rust off the cans and bugs out of the water. Or just paint the insides of the cans. Again, great job! I look forward to making my own.

[@guilldea]

The gods of audio have provided

[@fullwaverecked]

Great video! I should check the blender and the toaster.

[@ElPasoTubeAmps]

Before you throw them in the trash can, do the math, I=E/R... Stay safe...

[@fullwaverecked]

@@ElPasoTubeAmps I'm only half kidding. I have an older blender with the buttons. I've been wanting to check the resistance.

[@ElPasoTubeAmps]

@@fullwaverecked I had a portable heater the other day that I considered parting-out before I threw it away as I might need the heater coil some day for a dummy load. I ended up just putting it in the alley intact because it did work somewhat and someone actually may need it. Lots of the stuff we put out in alleys disappears overnight and usually ends up in Mexico. The pickups haven't been as regular lately because of the virus and many people can not come across the border into the USA.

[@fullwaverecked]

@@ElPasoTubeAmps I hear you. These are strange times indeed. That was an imaginative build re: 8 ohm load tank. Really cool. Thanks!

[@fullwaverecked]

@@ElPasoTubeAmps I'm seriously considering making one of these! Simple yet highly effective design. And this video also brought back fond memories of an exchange I had a while back with Uncle Doug; we were joking about turning the waffle iron into a giant resistor, and it was making the toaster real noivous. ;)

[@tubical71]

Ok you´re finished on your excellent 7kW dummy loads, next is to hook it up to your latest Tube Amp and see if you´ll make them cook or just boil water. Please use destilated water only or the will not last very long in hot normal water. Or fill the can with oil, simply use the old one when you change your car´s oli ;)

[@catdumpling]

this is pretty nifty! i wonder if there'd be any benefit to using antifreeze, perhaps the "pet friendly"/non-toxic kind. or maybe mineral oil? then again, i'm not an engineer, so take that for what it's worth;). someone else mentioned distilled water and that would probably be a good idea, just to keep any potential corrosion issues at bay; i know the computer overclocker crowd uses it for that reason.

[@pointdexter3606]

+catdumpling Prolly mineral oil would be better. Ever smelled Hot antifreeze? point

[@59seank]

Brilliant!

[@tubical71]

Next is: please do not worry to much about the resistance changes. They do not chage very much, as they are intened to be used on mains. So if the resistance are falleing they draw more current and either setting off the fuse or go burning stuff. Instead of doing this, they got positive temperature coefficient, so the resistance does indeed go up, when there are dissipating very much heat. Cook one on your bench via the variac in air and see what happen...;) As I done it some years ago and found out that its resistance raised until it opened.

[@ElPasoTubeAmps]

Well, you described it perfectly - keep them in water and cooled to a temperature for what they were designed for because in open air they will burn up - pretty obvious that they can not dissipate multi-killowatts of power all by themselves as there is simply not enough mass in them - thanks for your comments. I am picky about the resistance being accurate and stable as I am constantly measuring power - I have some of the cheap sand-block type 8 ohm 200 watt resistors but their temperature coefficient is absolutely horrible and will drop to 5 ohms when they are not even very hot and they aren't even 8 ohms when cool - I consider those type of resistors junk.

[@tubical71]

That is why the cheap - they are crap....no one would use them if they where not dirt cheap! ;)

[@judges69]

Perfect

[@Bobcat-UDX109]

I know it is late but here is a question... if you are using this to repair guitar amps typically 50 watt but no more than 100 watt at most..... would you need to worry about immersing the elements in anything? Would the elements stand up to it alone or do you really need the heat sinking of the water/fluid? Thank you ... this is brilliant and inexpensive!

[@ElPasoTubeAmps]

It would be a good idea to immerse the hot water heater element in water as it is fairly small and can not withstand dissipating more than 50 watts of heat (at the most) without some medium to dissipate the heat simply because of its size. If you don't want to deal with liquid, there are other conventional resistors that will work just as well. The best ones I have are from www.mouser.com and are non-inductive and about $60 each at the 300 watt level. There are cheaper ones on Ebay. I made this dummy load because, at the time, I was dealing with KW level amplifiers and did not have fixed resistors that can handle that much power.

[@Bobcat-UDX109]

@@ElPasoTubeAmps Thank you ! That makes great sense!

[@kgsalvage6306]

Does it make a difference with other wattage or voltage elements? I noticed yours are 3500 watt 220v. Would 240v still be 16 ohm?

[@CoquiAudio]

wow 8.1 ohm nice man :)

[@pointdexter3606]

+vargasmongo3435 Yes very cool huh! point

[@fullwaverecked]

So, would one single element give us half the ohms? I.e: 4.05 ohms? That would be handy. Thanks for posting!

[@ElPasoTubeAmps]

Each element is 16 ohms so in my video I have two of them parallel for 8 ohms. Using these same elements, it would take four in parallel to make 4 ohms. If you look at other elements like in Lowe's, do the math of, Resistance = voltage squared divided by power (watts)

[@fullwaverecked]

@@ElPasoTubeAmps Damn, just goes to show no matter how counter intuitive the basic concept is (i.e. MORE ohms = Higher resistance) the best policy is DO THE MATH! Your videos contain enormous amounts of knowledge, and being new to the hobby, I just assumed half of 8 would be 4. My bad and thank you for the reply. So, two elements in series would still be 8 ohms? And if so, you would need four elements combined in series & parallel to achieve 4 ohms? I'm not lazy. I've been googling the dog out of this and I've not yet rapped my mind around this and I appreciate you taking the time to reply.

[@ElPasoTubeAmps]

@@fullwaverecked You are getting close but keep in mind that each individual hot water heater element is 16 ohms. If you put two of them in Series, they will double and become 32 ohms. If you put two of them in Parallel, they will half and become 8 ohms. If you want to make 4 ohms out of 16 ohms, you would need to put four heater elements in Parallel and then the 16 ohms will reduced to 1/4 the value of a single element and be 4 ohms.

[@fullwaverecked]

@@ElPasoTubeAmps I see. Thank you for clarifying.This is a very interesting subject. BTW. What are your thoughts regarding combining a 120w dim bulb tester with a 120w dummy load?

[@ElPasoTubeAmps]

@@fullwaverecked A bulb dimmer needs the full 120 volts to work to drive the circuits within the dimmer so that is not going to work for a variable dummy load. Be nice if it did...

[@bobbarcus8310]

What were those long things that go in the water?how did you put them on? For us guys who do not know a.lot you kind of pass us over...thanks again

[@skycarl]

Don't know if you found out by now, but those are the elements and they come with the unit. At least they do at Home Depot. Hope this helps.

[@johnnytacokleinschmidt515]

Electric domestic hot water heater elements.

[@Partsocaster]

How's this thing doing? Still around? Did you change to mineral oil or keep the water?

[@ElPasoTubeAmps]

+ShooterReady It is still in my shop and came in really handy for the 813 amp I recently built. I left water in it as I don't want a leak of oil all over my shop. Water does a sufficient job of dissipating the heat. Fortunately, it has not leaked at all. The elements are still in good shape. It needs a stirring motor as the top gets hot and the bottom stays cold. The lid of the can started getting a little rust on it so I removed it, cleaned it, and painted it with wrinkle grey.

[@Partsocaster]

+ElPaso TubeAmps Nice. I have been bitten hard by the tube bug. RF mostly, but I did build myself a little guitar amp running a pair of 7189As. My problem is I'm about 30 years too young and have no "junk box". Tube iron is ridiculously expensive.

[@ElPasoTubeAmps]

I agree that some of the vacuum tube stuff on Ebay is ridiculously priced but sometimes you can find good stuff at estate sales for almost nothing.

[@frankgeeraerts6243]

haha , seemed a happy find...........just what about induction of the elements, did you check ?

[@ElPasoTubeAmps]

See my comment at top of video. BTW - this setup does not work for RF even at 14 MHz but it is great for AF.

[@frankgeeraerts6243]

Thanks , i missed to read the top comment :( ....always a pleasure to view your videos and for sharing your experience.

[@thirdroompro]

Man I was looking at 150 dollar dummy loads. However, what if your working on a 4 ohm or 16 ohm transformer amp?

[@ElPasoTubeAmps]

+Blake Thompson Each of these heater elements is 16 ohms so you could use just one but for 4 ohms you would need four in parallel. If you are not making exacting measurements where you need 1% tolerance and a very low temperature coefficient so that the load stays right on 8 ohms hot or cold, there are a number of dummy loads available for reasonable prices. Large 8 ohm wire wound resistors are fine as the inductance is low enough they will work just fine. Two 8 ohm resistors may be all you need. Put them parallel for 4 ohms or series for 16 ohms or just one for 8 ohms. Here is a listing on Ebay www.ebay.com/itm/2pc-8ohm-8R-100W-Watt-Power-Metal-resistor-for-tube-amp-test-dummy-Load-/201057901616?hash=item2ecffc1c30:g:qXUAAOxyUgtTLbB0 Some of the best 300 watt 8 ohm resistors are from www.mouser.com The part number is "ARCOL NHS300 8R F" and are $70 each. Hope this helps.

[@pointdexter3606]

you dont get any leaks? What do you seal both can half's with? Thanks Point

[@ElPasoTubeAmps]

+Point Dexter I soldered it with regular solder inside the cans (plenty of flux) and I believe afterwards, a bead of Goop, and some tape on the outside just for good measure and strength (and to cover any of the irregularities). Admittedly, I am surprised and pleased it has not leaked also.

[@pointdexter3606]

right if it did you would have 2 gals of water. Not good in a electrical shop :), And subscribed. thk you. Point

[@dambuster6387]

Is it filled with water or oil.

[@ElPasoTubeAmps]

+Martin Bernstein It is filled with water. That is a beautiful receiver you have on your KZbin picture. It says RCA but sure looks like a late 1940's Collins receiver.

[@dambuster6387]

Its 100% RCA Camden NJ built 1944 vast majority were sent to UK and Russia during the second world war, lend lease. I believe they are very scarce in the USA and command a high price.

[@calescapee9642]

Egad! I like that! I`m a moron.

[@DJSpecialistslimos]

Can you build one for me?