Originally posted by DrGonz78
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Dummy Load question
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Add a fan too.
My bench loads came up to my patch panel, and using the jumpers I had for the panel, I could configure various load impedances. I agree that is a handy side effect of making one up from smaller units.Education is what you're left with after you have forgotten what you have learned.
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Not that it should matter terribly if you're testing a 4 ohm output at 5 ohms or 3 ohms. But everybody seems to think it does.- Own Opinions Only -
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Originally posted by Helmholtz View PostFor SS amps with close to zero output impedance it does matter. As output voltage essentially stays constant, the power delivered into 3 Ohm will be up to 66% higher than with 5 Ohm."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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Originally posted by Enzo View PostAdd a fan too.
My bench loads came up to my patch panel, and using the jumpers I had for the panel, I could configure various load impedances. I agree that is a handy side effect of making one up from smaller units.
I also have an old GenRad 1396B Tone Burst Generator that does the same thing, while being able to use any signal source you want. (I regularly use the 1396B together with a GenRad 1382A Pink Noise Generator with a Krohn-Hite 3550A filter for setting the noise bandwidth as desired. Usually set for 2 Sec on, 3 sec off as the rep rates) Very few of us have Audio Precision analyzers or Sound Technology 3100B generators, both of which have dual level Tone Burst modes, allowing either counted cycles, on/off times, as well as setting the Off time as a dB level below the On time. Any of these allow the use of your limited wattage dummy load, which will normally handle short bursts of power into the load well above the steady state power rating.Last edited by nevetslab; 12-26-2018, 10:50 PM.Logic is an organized way of going wrong with confidence
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I make my own with precision and for peanuts out of cheap spiral wound nichrome wire intended for ultracheap food heaters (probably forbidden in lawyer happy First and Second World for safety reasons, since live and red hot wire is exposed).
You can not solder it so eyelets or screws are needed for contact.
Use them straight for low power tests (up to 100W), add a fan or drop (200W) them in a bucket of water or oil for scary high power dissipation (400W each resistor section) .
made for these:
Just stretch wire , measure 8 ohm sections, cut and mount each, combine as needed.
Remember mounting base must be insulating, resist red hot temperatures and , if used wet, stand water or oil.
I use Micanite, which is the sheet material normally used for such purposes .... wrongly called Mica which it is not.
Micanite is to Mica what chipboard or MDF is to wood.
You can get both out of a cheap hair dryer:
Notice the elements I mentioned: nichrome wire, micanite and eyelets.
You may even add an external power supply for the motor and fan and kludge an air cooled load resistor.
Motors are typically 6 to 12V or thereabouts and run in series with heater resistor, that´s why I suggest an external independent supply.
Here you can see the bridge rectifier so they get DC for motor.Juan Manuel Fahey
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I like the waffle iron thingy. You can test your amp while toasting a snack"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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I think the nichrome is also used in clothes dryers?
One thing I do like to make sure of with non-conventional loads is that the resistance does not increase when under full power it will be used at. (check that current verifies with voltage for stated resistance)Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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I remember that Heathkit used to sell a dummy load built into a 1 gallon paint can filled with oil. IIRC it was an RF load meant to take the place of an antenna. At the time I did not understand what it was for. I was just browsing my Dad's Heath catalog looking for HiFi kits.Keep learning. Never give up.
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The Heathkit dummy load built into a gallon paint can was called the...
Cantenna
https://www.orcadxcc.org/content/cantenna_va7jw.pdfEducation is what you're left with after you have forgotten what you have learned.
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Originally posted by Enzo View PostThe Heathkit dummy load built into a gallon paint can was called the...
Cantenna
https://www.orcadxcc.org/content/cantenna_va7jw.pdf
I bought it in the early 80s.
You have to furnish your own oil.
I tuned my KW ham amp into it.
Worked great.
T"If Hitler invaded Hell, I would make at least a favourable reference of the Devil in the House of Commons." Winston Churchill
Terry
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I found a good deal on a Milwaukee ribbed wire wound 4 ohm 420 watt resistor. Would this be a good one to get? The price is like $25 or something.
https://www.vishay.com/milwaukee/ribwound/When the going gets weird... The weird turn pro!
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Originally posted by DrGonz78 View PostI found a good deal on a Milwaukee ribbed wire wound 4 ohm 420 watt resistor. Would this be a good one to get? The price is like $25 or something.
https://www.vishay.com/milwaukee/ribwound/Keep learning. Never give up.
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