I don't understand why, but I'm having a very interesting situation here.
As I wrote in earlier posts, I used to have temperature issues: my grey 30x24x4 cm heatsinks became scorchin' hot, after a couple hours or more, even at a bias point of around 210 mV.
I learnt that heatsinks rely a lot upon irradiation, and they should be black for best efficiency. So I managed to have them anodized in black for free.
Put the amp together again, fired it up at 250 mV target. About the same high temperature I felt before at 210 mV... An improvement, but I hoped it would have become better (to reach 300 mV).
After a few days of use, I touched it again and felt it was cooler. Now I can handle 300 mV across the power resistors, while keeping my hand on it forever. Surely hot, but not so much as before.
So, it seems there's something I miss... How is it possible that the overall behaviour has changed in a few days? Maybe the black anodization has a "burn-in" time before "melting" into the aluminium and work properly? (I hardly believe it's true)
I can't understand why, in the first day of "black", I had a scorchin' hot amp at .5A, and now I have a warm/hot one at .6A.
Surely I'm very happy, it's finally over and working at full specs.
Giacomo
As I wrote in earlier posts, I used to have temperature issues: my grey 30x24x4 cm heatsinks became scorchin' hot, after a couple hours or more, even at a bias point of around 210 mV.
I learnt that heatsinks rely a lot upon irradiation, and they should be black for best efficiency. So I managed to have them anodized in black for free.
Put the amp together again, fired it up at 250 mV target. About the same high temperature I felt before at 210 mV... An improvement, but I hoped it would have become better (to reach 300 mV).
After a few days of use, I touched it again and felt it was cooler. Now I can handle 300 mV across the power resistors, while keeping my hand on it forever. Surely hot, but not so much as before.
So, it seems there's something I miss... How is it possible that the overall behaviour has changed in a few days? Maybe the black anodization has a "burn-in" time before "melting" into the aluminium and work properly? (I hardly believe it's true)
I can't understand why, in the first day of "black", I had a scorchin' hot amp at .5A, and now I have a warm/hot one at .6A.
Surely I'm very happy, it's finally over and working at full specs.
Giacomo
giacomo_pagani said:
Are you sure?
Yes, black will help but I beleive the benifit will not be more than 5-10% at most
Radiation... Yes, that's how it works. Is the amp in a more open air atmosphere now than your original temp measurements?
There is very little that would "break in" to make temp lower and nothing that would cause a change as much as you seem to be describing???
Are you measuring all the source Rs or just one?
Are you waiting the same time before you take a temp measurement. The profile of temp probably rises fast at first and overshoots then goes down then back up etc...
You might consider measuring the R of your source Rs cold, and then again hot. And then, measure the voltage drop on them again
Can you actually drive the output with a resistor load and swing the voltage(current) you expect???
It is more likely the excessive heat has changed a component permanatly only making the actuall current lower, not actually lowering the temp with the correct current.
