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Why pull and redo power transistors on the heatsink

whoaru99 said:
I'd use 1/3 continuous rated power (sine wave signal). That is a very demanding operating point.

Frankly, it's probably not even necessary to push that hard for the experiment. We're just looking for a change in the heat signature, not trying to blow it up. LOL.
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I concede this point - I don't always know what I'm doing!
 
jstang said:
One more.... what the hell, you can thank for doing your google searches for you.... its all relative....

https://www.sciencedirect.com/science/article/pii/S002627141300139X

TIM = Thermal Interfacing Material = Heat Sink Compound....

"For high-temperature applications, the effect of the degradation of the TIMs on the thermal performance of power switch modules must be taken into account for ensuring long-term operation."

Again its Temp x Hours = aging.... its more than reasonable to replace the stuff after 45 years....
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Good stuff there.
Looks like we're using a polymer based compound for our work? I'll have to look to see exactly what I have at home (bought it based on a recommendation here on AK).

Also looks like under 150°C (300° F) degradation either isn't significant or... from that study...

"Despite the wide research and development of the various TIMs described, there is a lack of data about their long-term thermal performance for high temperature power electronics applications. "

My brain hurts.
EDIT: But really, the one thing you said which makes the most sense to my lizard-brain.
"After 45 years....."
Yup
 
Soldering would be the way to go...

But you might need to dismount the xter from the heat sink to get it hot enough....

And that might ruin the test by disturbing the old Heat Sink Compound... At least to some degree ruin the test....

Have you ever tried to solder to a heat sink.... I did many moons ago...a da...you will get nowhere fast... :)


Dingman said:
Ya, that's pretty detailed. Drilling a hole, and peening the edges? Heh, not for me. At least they do give you the option of soldering the TC to the transistor case, that's fairly reasonable.

And ya, mine are T-type TC's and I have the two kinds -welded tip and film tip.

Maybe I'll do more measurements on this 2270 I'm working on now. I do plan on applying new pads and goop. Just for fun, you know. Har! :)
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its all about "temp x hours = aging process....." Plus how well the compound ages... And if the factory was having a bad day it made the stuff....

This is almost worse than the "Caps wear out discussion..2000 hours at 105*.." simply because the "Curing process" is miss understood....

This is like trying to tell people how the Hoover dam is still curing.... And they ask what do you mean? Its as hard as concrete now!

Yes but its still curing.....
 
jstang said:
Maggy's don't beat the crap out of amps.... thats the point.... And clipping ain't the same as power....amps clip at the same voltage with 16 or 4 ohms connected to them. The power at clipping into 16 ohms is very different than clipping into 4 ohms.... They need a current limiting circuit to limit power.... Blowing fuses does not mean you are using a lot of power.... What size fuse was it.... ?
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The right size fuse.

The amp got hot. I'm happy. Clipping is the limit of peaks, power is watts coming out. Can you tell me more about that and the 16Ω/4Ω difference and put something in for the 5Ω MGs and let me know? Nope blowing fuses in that particular circumstance was an indication of clipping. That is how my speakers react to amplifier clipping, they blow fuses, or drivers.

Now if I had used a nice pair of 'just name a bookshelf speaker' I would have caught them on fire running the amp that easily on the MGs. I know I have done it. What exactly is running an amp hard in your book because it is right and mine is wrong and I want to straighten out my idea of that. In a car analogy, I was driving with the throttle open to just below the fuel cut off and with maggies I was on the autobahn instead of the Laguna Seca so no gun the engine hit the brakes saw the wheel repeat, just gun the engine. Yes, I see how that could be 'easy' on and amp. Do it all the time. But what do you mean?
 
Look up how to calculate power..... P=E*I or you can derive it with the following P=E*E/R.

E is voltage, I is current and R is resistance.....

If the Amp clips at a constant clipping voltage.... some do and some limit the current too.... But lets use 40Vs as the on set of clipping...... then increasing R from 4 to 16 reduces the power.... Do the math in the second equation above.

Power is decreased and yet the amp is still at the on set of clipping....

40x40 / 16 = 100watts....
40x40 / 4 = 400watts

5 ohm Maggy's have almost no Reactive component to their IMPEDANCE because of their design.... and hence are a very stable amp friendly RESISTIVE load speakers....

Many 4 ohm speakers are highly reactive due resonance freqs..... and dip down way below 4 ohms........not very amp friendly.

Now lets say your difficult/reactive load 4 ohm speaker drops even lower to 2 ohms at the resonance Freq....

40x40 / 2 = 800 watts

Clipping.... raises the DC content in the signal.... Very bad for any speaker....pops the fuses if you have them.... can blow drivers without fuses...


But what does this have to do with Heat Sink Compound Aging ? Other than you were pushing your amp and speakers way too hard into clipping...and blowing fuses..... :thumbsdown: SHAME ON YOU FOR ABUSING YOUR MAGGYS ! :no: You sold gear? Come on, you should have known better...sales guys, always trying to make the next sale......:whip:

I have set of Maggys, they are too nice to beat on them....come on be nice to them :angel:

See, we knew there was a lesson in there somewhere..... :D

jk



Blue Shadow said:
The right size fuse.

The amp got hot. I'm happy. Clipping is the limit of peaks, power is watts coming out. Can you tell me more about that and the 16Ω/4Ω difference and put something in for the 5Ω MGs and let me know? Nope blowing fuses in that particular circumstance was an indication of clipping. That is how my speakers react to amplifier clipping, they blow fuses, or drivers.

Now if I had used a nice pair of 'just name a bookshelf speaker' I would have caught them on fire running the amp that easily on the MGs. I know I have done it. What exactly is running an amp hard in your book because it is right and mine is wrong and I want to straighten out my idea of that. In a car analogy, I was driving with the throttle open to just below the fuel cut off and with maggies I was on the autobahn instead of the Laguna Seca so no gun the engine hit the brakes saw the wheel repeat, just gun the engine. Yes, I see how that could be 'easy' on and amp. Do it all the time. But what do you mean?
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Thanks I needed that. The fuses popped once when I found out the limits of the eye candy indicators on the receiver. The fuses are there for a reason and this amp showed that reason. The meters are RMS reading according to the manual and at 10w everything was fine and with the amp lazily driving the maggies and getting hot doing it. A few days later I did probe higher indications on the meters just to see what was up with them and although they are set up to read the full output of the amp, the speakers objected at the 20-50watt indication, well below the range some would be driving their units and the amp is clipping. Now I know some seriously overdrive their system when getting the meters to swing all the way over. The level I was at the system was fine at half way plus a needle width or two and another notch up was too much. The far side of the meters never see the needles. Discussed in the Sansui forum.

Now I'm still at a loss as to how one drives an amp hard. Watts is watts, voltage is voltage and driving it to clipping is getting all it can give at that impedance. The FTC said an amp needed to be preconditioned and apparently that is an easy test for an amp because it is into an 8Ω resistive load. but amps reach thermal shutoff doing this test. I just need to use a variable load with reactance to drive an amp hard?

No not trying to sell anything, not a sales guy I was hired because I audio equipment knowledge not sales ability. They are my maggies, I can abuse them if I please. There is nothing special about them, they are completely rebuildable to brand new today by the factory, so no worries. They not an endangered species like so many other vintage pieces. I was being nice to things, I said I was beating the amp and you come in and say no you were babying that amp into a nearly purely resistive load. And that part of your post is what you needed to bold? Really? If someone drives an amp to thermal shutdown is that driving it hard or do we have to get out all the test equipment and measure the reactance of the speakers? Isn't dumping a significant amount of the amps power into the heatsinks enough?

I brought this up to discuss the temperature across a heat sink but then you needed to troll each answer to make sure everyone was completely in line with test procedures that you might use or accept. My posts went off the rails when I babied my speakers dumping a high output level of the receiver into them and discussed those temperatures and you got all bent out of shape about the my comment about driving the amp hard when you know it is driving it easy. Oh well, back on point now, you can have this thread and I'll go play in a different sandbox for a while.
 
Really? You asked for references....you wanted to test... Now you have details on how to test and attach the TC to xter.... References to happens to heat sink compound over time ....

Wait till the Russians start posting fake audio tech....then it's all down hill from there....

whoaru99 said:
It's fine for a forum, but thanks for all the words of discouragement. ;)
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Blue Shadow said:
...The FTC said an amp needed to be preconditioned and apparently that is an easy test for an amp because it is into an 8Ω resistive...
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The FTC preconditioning is not an easy test.

Is it the worst possible test one could contrive? No, but I don't believe the preconditioning test is intended to break the amp nor explore its endurance limits (but some are revealed during it).

It's intended to run the amp hard before the formal measurments and that it does, very, very well. More punishing than pretty much any semblance of music playback. You read that all the time in reviews and tests reports. The amp became quite hot during preconditioning but never much more than warm during the listening review.
 
jstang said:
Really? You asked for references....you wanted to test... Now you have details on how to test and attach the TC to xter.... References to happens to heat sink compound over time ....

Wait till the Russians start posting fake audio tech....then it's all down hill from there....
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Naaayyy naaayyy...
 
I'll see your trolling and raise the trolling... What does fuse blowing have to do with the long term performance of heat sink compound...?

Blue Shadow said:
I brought this up to discuss the temperature across a heat sink but then you needed to troll each answer to make sure everyone was completely in line with test procedures that you might use or accept. My posts went off the rails when I babied my speakers dumping a high output level of the receiver into them and discussed those temperatures and you got all bent out of shape about the my comment about driving the amp hard when you know it is driving it easy. Oh well, back on point now, you can have this thread and I'll go play in a different sandbox for a while.
Click to expand...
 
This is the stuff I use, have done for decades and it's good:

• Composition:
• - Dimethyl Polysiloxane (silicone) 28%
• - Zinc Oxide 65%
• - Submicroscopic Pyrogenic Silica 4%
• - Stabilizer 3%
• General Physical and Chemical Properties:
• - Colour: Opaque White
• - Odour: None
• - Consistency: Penetration, worked and measured within 1 minute after working (ASTM D-217) = 260
• - Bleed (after 24 hours @ 200ºC): 1.0%
• - Evaporation (after 24 hours @ 200ºC): 1.0%
• - Specific Gravity at 25ºC: 2.3
• - Thermal Conductivity, K Factor, cal⁄cm²⁄ºC⁄sec⁄cm: 0.0015
• - Dielectric Strength, kV at 0.1mm, ASTM D-149: 1.0
• - Boiling Point: >250ºC
• - Melting Point: 1,970ºC
• - Flash Point: 230ºC
• - Auto-ignition Temperature: 425ºC
• - Vapour Pressure: >2hPa
• - Relative Density: >⁄= 2.1 (@ 20ºC)
 
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