The max amp temp is not specified, nor is the amp temp rise in operation. Plus, the temperature of the amp relative to room ambient is totally dependent on the location of the amp and the airflow around it.
You aren’t wrong. I just don’t know how to apply the manual recommendations without more data.
I didn’t ask what it means, I asked where I should measure it. It seems clear that the manual is saying “if the amp is in an enclosed space, you need to measure the ambient temperature in that space”.
So if I put the amp in a cabinet, I need to know the temp in that cabinet. Should I put my temp probe on the bottom of the cabinet? The top? The side?
During "Agency Testing" we measured Ambient temperature in the proximity of the UUT (Unit Under Test) under normal operating conditions in a temp chamber. We normally used three thermocouples placed (1) 4" in front of the UUT, (2) 4" to the right of the UUT, and (3) 4" to the left of the UUT. This was for panel mounted equipment.
Since this is shelf mounted UUT, measure in front, behind, and to each side under normal conditions. If in a cabinet, and you plan on running it with the door closed, then do so for the test.
Take the "ambient" temp to be the average for the four readings.
Keep taking readings until the temps stabilize.
Since this is shelf mounted UUT, measure in front, behind, and to each side under normal conditions. If in a cabinet, and you plan on running it with the door closed, then do so for the test.
Take the "ambient" temp to be the average for the four readings.
Keep taking readings until the temps stabilize.
OK, sorry to be a bit short. I agree that that spec is somewhat ambiguous. TheGimps' advice above seems sensible.
The idea is that the final temp of the amp internals is the ambient + the temp rise of the amp due to dissipation.
Apparently, they know the temp rise so by specifying max ambient they keep the amp temp under control.
In effect, the ambient is the temp of the air that is used to cool the amp, whether it is by forced ventilation or by natural convection.
The assumption with that is that the ambient does not change from the amp dissipation, which is only valid in large spaces.
If you mount the amp in a smallish cabinet, the cabinet temp will also rise which means the ambient will rise.
So if you mount the amp in a small cabinet, take an extra safety in account by downgrading the max allowed ambient.
Jan
Thank you! This is exactly what I was looking for. I'll get some sensors and take an average like you suggest.
@jan.didden No worries! The manual was unclear. I think I will take @TheGimp's advice and use several sensors to get an average temperature within the space where the amp is located. Then I'll make sure that temperature stays below 50C when the amp is operating, as per the manual. It if exceeds 50C I will work out some sort of active cooling solution.
The ARC rating, like most, intends for the amplifier to be in free air, on a flat surface, with unimpeded air circulation around it.
In a cabinet or rack, with restricted circulation, would likely require fans to remain within spec (as ARC used at one time).
Measuring the air temperature inside the cabinet will not correct the basic problem of impeded air circulation,
while the spec assumes free air placement.
A much higher ambient temperature than normal, plus the impeded air circulation, will not allow adequate cooling.
In a cabinet or rack, with restricted circulation, would likely require fans to remain within spec (as ARC used at one time).
Measuring the air temperature inside the cabinet will not correct the basic problem of impeded air circulation,
while the spec assumes free air placement.
A much higher ambient temperature than normal, plus the impeded air circulation, will not allow adequate cooling.
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@rayma The section from the manual that I quoted is specifically for using the amplifier in an enclosed space:
That's why I think their definition of "ambient operating temperature" means the air temperature around the amplifier, which would be higher than the general room temperature if the amp is installed in a constricted space.
That's why I think their definition of "ambient operating temperature" means the air temperature around the amplifier, which would be higher than the general room temperature if the amp is installed in a constricted space.
Certainly if there are quote marks around the word ambient, that does not refer to the standard ambient temperature.
Perhaps "ambient" refers to the air intake temperature, near the bottom of the amplifier. It's highly doubtful that
an ARC amplifier could have a normal useful life with the 120F air intake.
ARC used to sell a rack mount fan assembly for use with their tube amplifiers, not cheap.
https://www.arcdb.ws/model/FB1
https://www.arcdb.ws/model/FB2
Perhaps "ambient" refers to the air intake temperature, near the bottom of the amplifier. It's highly doubtful that
an ARC amplifier could have a normal useful life with the 120F air intake.
ARC used to sell a rack mount fan assembly for use with their tube amplifiers, not cheap.
https://www.arcdb.ws/model/FB1
https://www.arcdb.ws/model/FB2
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The D-70 can draw air in from below, but it has to move around the main PCB, maybe 3/4” gap all the way around. The cage is open on the top and sides, but weirdly not the front or back.
Later ARC designs had fully-perforated cages, and placed fans either at the back, or at the bottom (these designs rotated the tubes 90* to facilitate clean airflow bottom to top)
I’m not sure if I should try to vent exhaust heat out the back of the cabinet, or apply direct circulation to the cage. The later is complicated by the two large filter caps that separate the two channel’s power tubes. I could mount a fan on each side blowing across the tubes, or sucking hot air out of the cage.
Any thoughts on what active cooling solution would be best?
Later ARC designs had fully-perforated cages, and placed fans either at the back, or at the bottom (these designs rotated the tubes 90* to facilitate clean airflow bottom to top)
I’m not sure if I should try to vent exhaust heat out the back of the cabinet, or apply direct circulation to the cage. The later is complicated by the two large filter caps that separate the two channel’s power tubes. I could mount a fan on each side blowing across the tubes, or sucking hot air out of the cage.
Any thoughts on what active cooling solution would be best?
Measure the temperature within the cabinet with the amp running for a while. The only temperature that matters is where the amp is running. It is designed to function properly at surrounding temps of up to 50C but less is better to prolong part life. Measure just above the surface but not touching it. The top of the cabinet may well exceed 50C but it’s where the physical amp is that matters. Fans pulling air out are better than ones that blow on the amp in a sealed cabinet. Locate holes on the bottom back and put the fan blowing out at the top of the cabinet back. This pulls cool air in and through the cabinet which is better than cramming more air in the cabinet along with the existing hot air. run a fan at lower voltage to keep noise down and two fans are better than one. Put several 2” holes along the bottom of the back. Smaller holes increase velocity which is a good thing to blow the hot air away from the chassis. These are all tried and true methods of cooling we use professionally to keep equipment cool and happy. If the cabinet has no back or front doors make sure there is enough room above the amp for the heat to rise, I like minimum of 12” above the top of the tubes and more is better. Tubes must be hot to run but resistors and caps like it cool to be at their best so give the heat a way out so it doesn’t cook the guts of the amp.
I would cut holes for two fans in the back of the amplifier cover, and blow cool intake air onto the tubes,
after which hot air would flow out of both sides. The fans will also last longer as intake fans.
In addition, other fans mounted on the cabinet itself may also be useful.
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Back is completely open. Front is somewhat constrained, but should have a good 1.5” gap around the sides and the top. My initial idea is to place vent fans at the top corners behind the amp.
I would prefer not to modify the cage, but perhaps mounting fans on the top could work? Either blowing up, sucking cool air in from the sides, or blowing down, forcing air over the tubes and PCB and out the sides?
I’ve ordered an AC fan controller that can drive up to four PC fans with variable voltage control, as well as a four-probe thermometer. As long as I can keep the noise down, I’ll throw as many fans in there as I can fit.
Picture attached for reference. I could also run without the cage for additional airflow.
I would prefer not to modify the cage, but perhaps mounting fans on the top could work? Either blowing up, sucking cool air in from the sides, or blowing down, forcing air over the tubes and PCB and out the sides?
I’ve ordered an AC fan controller that can drive up to four PC fans with variable voltage control, as well as a four-probe thermometer. As long as I can keep the noise down, I’ll throw as many fans in there as I can fit.
Picture attached for reference. I could also run without the cage for additional airflow.
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Two layers of perf would restrict the air flow much more.
Then I'd just leave the cover off, and mount the fans elsewhere in the cabinet.
Low for intake, or high for exhaust, or both.
Then I'd just leave the cover off, and mount the fans elsewhere in the cabinet.
Low for intake, or high for exhaust, or both.
The electrolytic capacitors are the weakest point.
I wouldn't worry about the tubes with the cover off.
But the output tubes generate most of the heat, so you want as much of that as possible
to go right up and out of the amplifier. Some heat will still be conducted to the socket and board.
I wouldn't worry about the tubes with the cover off.
But the output tubes generate most of the heat, so you want as much of that as possible
to go right up and out of the amplifier. Some heat will still be conducted to the socket and board.
The goal is not to cool the tubes but get the hot air out before it cooks everything else. The cage will literally make a fan blowing on it worthless, air takes the path of least resistance so it will hit the perforated metal and spread out but very little will go through. Mounting fans on top of the amp bolted to the perforated metal sucking air out will help the most. There will be a lot of resistance to flow because over half the area will be solid but a good fan will suck out more than would normally just flow out from convection alone. Two fans, one over each channel would work.the larger the fan the better. 8” fans are available in both 120 and 12volt you might even want to block off the holes on the top and upper sides of the cage to force air from the bottom up through the whole amp. The path of least resistance again, if the air can cheat and avoid going a long way it will so instead of being drawn across the whole amp it would just be sucked in right next to the fan on top. Blocking the holes in the non fan area would force the air to do what you want, pull the hot air out through the amp.