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Old 25th February 2016, 11:26 AM   #1
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Default 1943-5200 temperature issue

Repaired one amplifier which is working and biased according to specs in "class A " which in real life means high bias class AB

The specific application is 4 output transistors per ch supplied with 38+38 volt and each transistor is biased at 410ma which is a bit lower than specified in the manual

HTC is all brand new, plenty and fresh everywhere and the mechano work is done as best is possible everything is very tight considering the assembly

The result is about 57 degrees on the mount area of the transistors while fins of the heatsink will be a few degrees lower ...

Do you think that this is safe enough ?
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Old 25th February 2016, 12:01 PM   #2
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Semiconductors; Power dissipation starts to degrade above 70 C.
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Old 25th February 2016, 12:05 PM   #3
AndrewT is offline AndrewT  Scotland
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One would need to do a simulation for the temperature de-rated SOAR to compare to the loadings imposed on the output stage.

That is not a quick bit of guesswork.
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Old 26th February 2016, 12:31 AM   #4
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by east electronics View Post
Do you think that this is safe enough ?
I do. Because for most normal listening levels this amp will stay in Class A. It has 400mA x 4 = 1.6A per side. Into 8 Ohm that's 10W already and with Class A the more the music plays the more power goes into the speaker and less for the transistors.

But what about the ambient - you have a nice cool workshop, will customer use it in Greek summer when it is 30C in the house ??

Maybe put a temperature cut-out switch on the heatsink and put it in series with power supply.
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Old 26th February 2016, 09:35 AM   #5
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Proper vbe multiplier exists in both ch located in proper area and double thermal cutoff separated for both ch exists already in the amplifier .

Thanks Gareth !
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Old 26th February 2016, 05:59 PM   #6
44ct357 is offline 44ct357  South Africa
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chuck the junk in the bin and use tip35/36C from st micro, make sure same batch number for audio perfection!
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