The difference between 200 and 300 is the efficiency of a linear supply. As such, both figures are absolutely correct.
I was almost able to understand Zen Mod's joke 😎
But in the example (below) there is a difference between:
TJ=16 * (1 + 1 + 2) +25
and TJ = 116
16 * 4 + 25 = 89
But Tj is 116
116 - 89 = 27
And now i can't sleep, what is this 27 and where did it come from?
Keratherm claim the thermal resistance (Rth) of their red 86/82 thermal pads is around 0.1 K/W. http://www.kerafol.com/fileadmin/us.../01-standardfolien/Datenblaetter_TM_86_82.pdf
Has anyone had a chance to confirm it?
I did a quick comparison verse generic silcone thermal pads and the keratherm pads are significantly better.
Has anyone had a chance to confirm it?
I did a quick comparison verse generic silcone thermal pads and the keratherm pads are significantly better.
I reported an anomaly a few years ago when in the testing phase of a paralleled output stage of a power amplifier.
I ran out of plastic/silicone insulators and used some thin mica to complete the test assembly.
The currents through the various paralleled devices were very different !
It was the lower temperature of the mica mounted insulators that caused the Vbe to be higher and this reduced the current in the mica mounted devices.
The silicone mounted devices thus had to pass a higher proportion of the current and as a result had to run even hotter, exaggerating the unbalance.
Changing to all mica mounted removed the unbalance in the 3pair output stage.
Thanks Nelson. Setting out this detail clears up a few unknowns for me.
Equations work for me. I may not be an Elec Eng but heat transfer is part of what I do.
Equations work for me. I may not be an Elec Eng but heat transfer is part of what I do.
For me I tend to run conservatively on bias. I’m not so much worried about blowing up the output stage as I am about the speaker that is connected to it. That can be much more expensive to repair and sometimes parts may not be available.
My F5V3 is running about 22w/device. The heatsinks are less than 50c and the transistors don’t feel much warmer than the heatsinks. I used the Keratherm pads and torqued them to the recommended 10inch pounds. Heat transfer seems to be excellent. I’m not sure how much it would change the heat transfer ratings if the mounting torque is not high enough or is inconsistent from device to device. Nobody seems to be talking much about mounting torque so perhaps it’s not an issue.
My F5V3 is running about 22w/device. The heatsinks are less than 50c and the transistors don’t feel much warmer than the heatsinks. I used the Keratherm pads and torqued them to the recommended 10inch pounds. Heat transfer seems to be excellent. I’m not sure how much it would change the heat transfer ratings if the mounting torque is not high enough or is inconsistent from device to device. Nobody seems to be talking much about mounting torque so perhaps it’s not an issue.
Yes, they have a defined lifespan that is highly dependent on temperature. In an amp that runs hot they are kind of like a consumable item. The older big can type caps with the screw terminals on the top seem to be the best at lasting a long time under hot conditions. They are much bigger and more expensive so you only see them in high priced gear or in DIY stuff where the cost is justified by some builders.
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