Sorta non-issue for oil filled heaters.Thanks for taking the time to plot those. A non issue then
Anyone have a cheapo radiant bar fire they could test? The elements would get much hotter than an oil filled heater.
Moral : Use oil filled heaters for your dummy loads
Du..uh! Resistors in oil-baths were common at one time for just this reason
The horiz is frequency
The vert is resistance.
The different colours indicate the resistor type and where one can see also shows a different temperature.
I can see all of that.
I can also see a very slight increase in impedance at your highest frequencies. This probably indicates a small amount of inductance.
What is your method for arriving at these results.
How did you control the temperature of the resistor during the measurement of resistance?
It's the method I am interested in.
The vert is resistance.
The different colours indicate the resistor type and where one can see also shows a different temperature.
I can see all of that.
I can also see a very slight increase in impedance at your highest frequencies. This probably indicates a small amount of inductance.
What is your method for arriving at these results.
How did you control the temperature of the resistor during the measurement of resistance?
It's the method I am interested in.
OK, sorry - didn't realize what you were asking.
- The impedance sweeps were done with the WT3 sold by Parts Express.
- The resistor was at room temp. approx 22 C
- The radiator was heated until the thermostat kicked in. Don't know the temp, but the radiator was hot to the touch. The elements were likely hotter. Sweep was done within 10 secs of unplugging the radiator.
The oil-filled room-heater radiators that I own have a bunch of stuff I'd want to disconnect, like a tip-over shut-off, an over-temp shut-off, and an adjustable thermostat. My best one has a microprocessor pre-heat cycle, timer, remote control, and a bunch of other "automation" I don't want. Ingenious idea to use as a dummy load though!
Really consistent impedance driven to dissipate moderate-level wattages. They're physically oversized for the bench though, and a bit odd to lug to a gig. But I was thinking air-cooled or water cooled but didn't want any noisy fans, and the existing self-circulating oil-filled radiator space heater is actually pretty well suited to the task.
It seems to me that really huge high-wattage heater elements would be nearly perfect when not driven anywhere near their normal wattage.
So what's a really ideal dummy load, able to completely absorb high power if I choose to have no output, but with a balanced low-impedance line-level output and an unbalanced variable-level output, and a speaker output. In other words, I'd want it to handle high-power transistor amps for testing, all kinds of tube amps for testing or for low-volume recording or practice, or with a direct-out for stage.
The original altair power attenuator used nichrome heater wire, soldered to terminal. Nichrome doesn't solder worth a darn, and the wire got hot and melted the solder, so it didn't work out very well.
Tom Scholz Power Soak used arrays of sand-cast resistors. They got very hot, changed value with temp, and the resistors frequently cracked and failed, burned the circuit boards, unsoldered themselves, etc.
I don't know what the THD HOT plate uses. But they are not cheap and they expect you to buy one for each impedance.
The Marshall Power Brake had a multi-tap transformer and just one or two big resistors as I vaguely recall. I never did quite figure out the intent, except of course that it could make that single resistance match various amplifier impedance taps. If you really understand these units and the intent of the circuit, please explain it to me.
Thinking about parts first, I'd always thought that really good design would need high-current rotary or toggle switches, and would start with several high-wattage Calrod heater elements, like meant for an electric water heater, (just because they're cheaper than 1000-watt resistors) bolted solidly to a large heatsink, with switchable fans. Then, after the power is divided to 1/4 the original value or even 1/16, some kind of high-power switchable-level L-pad? A quarter-inch speaker out, and also another L-pad and a transformer for genuine balanced direct output (maybe a Dean Jensen BM-series) for line=level to a live or recording board. And switchable high-frequency and low-frequency filters too, since over-spec parts from crossover stock are not expensive at the greatly reduced levels.
I don't see a role for lightbulbs or anything that changes impedance when it gets hot, as either an indicator or as some kind of protective device that reduces the load on the amp after a while.
I imagine an air-cooled design with a significant vertical dimension for some kind of chimney and fans available only as a last resort when working on very high-powered transistor amps. Maybe some kind of removable fan top-hat or base?
So...I'd be shopping for multi-pole high-power rotary switches, Calrod heater elements, tall heat-sinks...and some common power resistors and crossover caps and coils.
Any good advice appreciated.
Really consistent impedance driven to dissipate moderate-level wattages. They're physically oversized for the bench though, and a bit odd to lug to a gig. But I was thinking air-cooled or water cooled but didn't want any noisy fans, and the existing self-circulating oil-filled radiator space heater is actually pretty well suited to the task.
It seems to me that really huge high-wattage heater elements would be nearly perfect when not driven anywhere near their normal wattage.
So what's a really ideal dummy load, able to completely absorb high power if I choose to have no output, but with a balanced low-impedance line-level output and an unbalanced variable-level output, and a speaker output. In other words, I'd want it to handle high-power transistor amps for testing, all kinds of tube amps for testing or for low-volume recording or practice, or with a direct-out for stage.
The original altair power attenuator used nichrome heater wire, soldered to terminal. Nichrome doesn't solder worth a darn, and the wire got hot and melted the solder, so it didn't work out very well.
Tom Scholz Power Soak used arrays of sand-cast resistors. They got very hot, changed value with temp, and the resistors frequently cracked and failed, burned the circuit boards, unsoldered themselves, etc.
I don't know what the THD HOT plate uses. But they are not cheap and they expect you to buy one for each impedance.
The Marshall Power Brake had a multi-tap transformer and just one or two big resistors as I vaguely recall. I never did quite figure out the intent, except of course that it could make that single resistance match various amplifier impedance taps. If you really understand these units and the intent of the circuit, please explain it to me.
Thinking about parts first, I'd always thought that really good design would need high-current rotary or toggle switches, and would start with several high-wattage Calrod heater elements, like meant for an electric water heater, (just because they're cheaper than 1000-watt resistors) bolted solidly to a large heatsink, with switchable fans. Then, after the power is divided to 1/4 the original value or even 1/16, some kind of high-power switchable-level L-pad? A quarter-inch speaker out, and also another L-pad and a transformer for genuine balanced direct output (maybe a Dean Jensen BM-series) for line=level to a live or recording board. And switchable high-frequency and low-frequency filters too, since over-spec parts from crossover stock are not expensive at the greatly reduced levels.
I don't see a role for lightbulbs or anything that changes impedance when it gets hot, as either an indicator or as some kind of protective device that reduces the load on the amp after a while.
I imagine an air-cooled design with a significant vertical dimension for some kind of chimney and fans available only as a last resort when working on very high-powered transistor amps. Maybe some kind of removable fan top-hat or base?
So...I'd be shopping for multi-pole high-power rotary switches, Calrod heater elements, tall heat-sinks...and some common power resistors and crossover caps and coils.
Any good advice appreciated.
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Way back when, after work we used a large primary resistor motor controller grid similar to this: http://www.filnor.com/html/images/ngresistor/NGR-silver.jpg
GM
GM
I've also looked at something from Weber, and Dr Z/trainwreck. And
Greg Perrines Recycled Sound Page
has attractive prices and a sensible floor-resident foot-switchable layout, but that external case can't really dissipate much for very long.
I might need to make multiple units that plug together in various ways, to satisfy all my needs.
Greg Perrines Recycled Sound Page
has attractive prices and a sensible floor-resident foot-switchable layout, but that external case can't really dissipate much for very long.
I might need to make multiple units that plug together in various ways, to satisfy all my needs.
For what you are trying to do, water heater elements sound like the ticket. There are a large variety made for both automotive radiator heating and home water heaters.
It takes a lot of power to boil off water, you could use a quart size container (or a little car heater coil for better thermal transfer of the water's heat) and empty the water for traveling and fill at the gig, even with a 10 dB soak on a 100 watt guitar amp I doubt the water would come to a boil unless you only play extended feedback solos
.Yes, GM, what we really want isn't always what we really need LOL. But somewhere I do have some really big resistors from that sort of thing. The ones I have are wirewound on hollow ceramic tubes, but the wire winding changes direction frequently to reduce inductance.
I was all gung-ho on using metal-cased power resistors bolted to heat sinks, until someone pointed out that the internal temp can resistance change can be significant. So I'd have to over-spec them, not for reliability but for consistent impedance.
I guess it's time to shop for some heater elements versus surplus power resistors and discover the truth.
I was all gung-ho on using metal-cased power resistors bolted to heat sinks, until someone pointed out that the internal temp can resistance change can be significant. So I'd have to over-spec them, not for reliability but for consistent impedance.
I guess it's time to shop for some heater elements versus surplus power resistors and discover the truth.
I'd prefer to keep a constant temp much lower than the state-change of water. And I don't really like mixing water and high voltage around drunks at a gig. But indeed it would work. But I'm thinking of using the water-heater elements without any water, at much lower wattages, bolted to very large heatsink.
I'm starting to narrow my focus on making several simple units that plug together with 1/4" plugs instead of switching (might normally have shorting plugs in some jacks):
1) A high-power 8-ohm dummy load.
2) A high-power 8-ohm series/parallel T-pad to reduce power out to 1/4 what comes in. I could plug the other dummy load into this unit's input jack section, in series (instead of a shorting plug) or in parallel, to change the load on the amp to 4 or 16 ohms. This unit could also be used with any commercial power soak and high-power amps, to reduce the power first.
3) Another 1/4 power reducer meant for lower power. I could use this after the original. Or just buy any commercial one.
4) A medium-power variable L-PAD (which would be relatively high-power for such a thing). Or could be built into any commercial one I buy.
5) A low-power high-cut filter, to eliminate hiss or make the distortion more 'creamy' and less objectionable. Meant to be used only at lower levels.
6) A low-cut filter for when I'm using little speaker cabs that just can't make bass.
Optionally:
7) A high-power first-order low-pass that I would plug into the parallel jack of a power attenuator for a profound bass-boost. Kind of expensive.
8) A high-power first-order high-pass that I would plug into the parallel jack of a power attenuator for a profound treble boost. Kind of expensive.
To start with I could build just #1 & #2 and buy an old used Scholz power soak. That would be really flexible.
There are all kinds of alternatives to the shorting plug for series connection in the #2. for instance, the #1 could have jacks to use it in parallel or series w/ #2.
Or #1 could just be switchable and built into #2. All these boxes and jacks and plugs could get unreliable and cumbersome.
- still thinking (typing) out loud (online)...
I'm starting to narrow my focus on making several simple units that plug together with 1/4" plugs instead of switching (might normally have shorting plugs in some jacks):
1) A high-power 8-ohm dummy load.
2) A high-power 8-ohm series/parallel T-pad to reduce power out to 1/4 what comes in. I could plug the other dummy load into this unit's input jack section, in series (instead of a shorting plug) or in parallel, to change the load on the amp to 4 or 16 ohms. This unit could also be used with any commercial power soak and high-power amps, to reduce the power first.
3) Another 1/4 power reducer meant for lower power. I could use this after the original. Or just buy any commercial one.
4) A medium-power variable L-PAD (which would be relatively high-power for such a thing). Or could be built into any commercial one I buy.
5) A low-power high-cut filter, to eliminate hiss or make the distortion more 'creamy' and less objectionable. Meant to be used only at lower levels.
6) A low-cut filter for when I'm using little speaker cabs that just can't make bass.
Optionally:
7) A high-power first-order low-pass that I would plug into the parallel jack of a power attenuator for a profound bass-boost. Kind of expensive.
8) A high-power first-order high-pass that I would plug into the parallel jack of a power attenuator for a profound treble boost. Kind of expensive.
To start with I could build just #1 & #2 and buy an old used Scholz power soak. That would be really flexible.
There are all kinds of alternatives to the shorting plug for series connection in the #2. for instance, the #1 could have jacks to use it in parallel or series w/ #2.
Or #1 could just be switchable and built into #2. All these boxes and jacks and plugs could get unreliable and cumbersome.
- still thinking (typing) out loud (online)...
the elements from electric kettles may be good for absorbing power without getting too hot.
A UK 3kW 240Vac element should have a hot resistance of around 19r2
The cold resistance is 20r8
A 2200W 240Vac element should have a hot resistance of around 26r2
The cold resistance is 27r5
The change from cold to hot indicates that the resistive element is running hot, much hotter than the water it has to boil.
It is surrounded by an insulator. Much the same as you have in an aluminium clad Power Resistor intended for attachment to a coolish heatsink.
Three kettle elements will make a good amplifier load. If each is only absorbing 100W or 200W then the element temperature will be much lower than when connected to mains power.
A UK 3kW 240Vac element should have a hot resistance of around 19r2
The cold resistance is 20r8
A 2200W 240Vac element should have a hot resistance of around 26r2
The cold resistance is 27r5
The change from cold to hot indicates that the resistive element is running hot, much hotter than the water it has to boil.
It is surrounded by an insulator. Much the same as you have in an aluminium clad Power Resistor intended for attachment to a coolish heatsink.
Three kettle elements will make a good amplifier load. If each is only absorbing 100W or 200W then the element temperature will be much lower than when connected to mains power.
For a dummy load "resistance wire" like nichrome or a carbon pile load is perfect. Carbon pile testers are available commercially and are very cheap. Use a Western Union splice to join the heater wire with regular copper leads then leave as is or add solder. Wire wrap the nichrome right to the terminal otherwise, as I have recently learned, wire wrap tools are expensive but easily improvised.
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