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Old 19th September 2003, 04:41 PM   #1
joensd is offline joensd  Germany
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Default Thermal switches

I´m thinking about to implement a thermal switch for my Aleph3.

The prior reason to use it is probably failure of the current source and so a too high bias current -> too high temperature !?
Or maybe for some very hot sommer to ensure things stay in the desired range!?

Now what do you think ?
Is it worth using it ?
Does anybody use them at all ?
Which one would you choose and where can I get them ?

Thanks in anticipation
Cheers
Jens
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Old 19th September 2003, 05:48 PM   #2
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I use thermal switches in my big amps.
You can get them at Farnell. Just place it on the heatsink and connect them to main AC to the toroid/transformer
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Old 19th September 2003, 05:56 PM   #3
Netlist is offline Netlist  Belgium
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Not a bad idea, the original Alephs have them too and switch off at 75 °C.
As for the current source failure, IMO you will hear it faster than the thermal switch can shut things down.
I'm not sure what you mean with 'the desired range'.
They certainly will not keep the amp at a constant temp. They only protect from overheating by switching off the PS.

Any decent switch will do, Farnell has several: http://de.farnell.com/jsp/catalog/vi...?prodId=491524

/Hugo
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Old 19th September 2003, 06:40 PM   #4
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Hi,

I also have them in my Aleph 5's. Conrad sells them, but you can probably also get them in your local electronics shop. I don't think they are really necessary (spelling???). However it is a nice feeling to have a switch there. Indeed when the summers get really hot. (desired range I suppose...). I agree however with netlist that a thermal switch is too slow if somekind of electrical failure occurs....


Greetings
Jan
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Old 19th September 2003, 06:53 PM   #5
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I use thermal switches quite often and they do work quite nice especially if you are not around .....I hooked one up so a fan started when the switch cut out on a relay and then stopped when the enclosure cooled down.....simple and elegant
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Old 19th September 2003, 06:54 PM   #6
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Thermal switces like these only protects against "long term" overheating, - not against rapid heating of the output transistors due to shortening or use with very low impedances.....

However I like to use them as an extra protection....
And it has saved me for buying several new output transistors
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Old 20th September 2003, 04:50 PM   #7
joensd is offline joensd  Germany
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Thanks guys fo the suggestions and ideas do far.
Will probably buy one at my next "parts-shopping".

Really like the song "burning down the house" but I don´t want to get that far.

Jan was right about the "desired range". I was talking about a certain temperature range the amp works at.

So I´ll try them and go for the extra protection.

Thanks!

Jens - will post results measuring the distortion with and without the thermal switches
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Old 20th September 2003, 06:00 PM   #8
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Quote:
Jens - will post results measuring the distortion with and without the thermal switches
If you insert the thermal switches in the AC primary (as I do) you won't measure any extra distortion......
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Old 21st September 2003, 01:55 PM   #9
joensd is offline joensd  Germany
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Quote:
If you insert the thermal switches in the AC primary (as I do) you won't measure any extra distortion......
Was that a joke too ?

Cheers
Jens
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Old 21st September 2003, 02:24 PM   #10
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Maybe it is just me being over-cautious, but I don't like the idea
of using a thermal switch on the mains side of the transformer.
It seems to introduce unnecessary safety hazards to have
mains leads that close to the heat sinks. A bad solder joint
may be sufficient for a lead to touch the heatsink and I need
hardly say what that means if the heatsink is connected to the
case or touchable.

Of course, it is a little bit more complex to avoid this problem.
Either use two thermal switches on the secondaries or use one
thermal switch that controls the mains indirectly through relay
or whatever.
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