Advice on replacing thermal cut-off on Sunn SS power amp

[Dreams]

I'm repairing an old Sunn Concert Slave and it's got a faulty thermal cut-off. I'd like to replace it, as it is the only real protection circuitry it's got. Problem is, I can't make out any make or part numbers, and the available schematic is too blurry to read.

I've never had to deal with one of these before, so I'm not quite sure what I'm looking for. Looked at Mouser/etc and didn't come up with anything, probably not looking in the right place...?

I imagine I'll need something rated for a certain temp, but I'm also at a loss for what that temp might be.

Any thoughts?

 

[joaquins]

125º at juntion, easy(ish) to touch at heat sink is rule of thumb. I would start at 90º for example, you could measure the temperature at normal conditions, and some loaded also, and get something a little over that... Use your worst case 'normal' use and step a bit for a warm day...

JS

 

[PRR]

Often "thermal cut-OUT".

The key point is to guess a Temperature. Transistors is transistors, so look on other Sunn SS plans for the number that Sunn designers liked.

Other point is that older gear mounted with two screws/nails and 1/4" tabs, while much modern stuff has switched to a cheaper construction with no mounting provision and bare leads. I do not know a keyword to sort-out the type you want. You can use the newer type, if you cobble the mounting and the wiring.

 

[Dreams]

Just an update here.

Went with this:
http://www.newark.com/white-rodgers/3l11-170/disc-thermostat-snap-action/dp/16M4635

A White-Rodgers 3L11-170 "Bimetal Disc Thermostat"

A bit of sleuthing got me a cross ref for the old part. Found a new part with similar temp ratings.

 

[CJ]

got a bag of those at work, for some reason they do not use heat sink compound on those,

 

[PRR]

> some reason they do not use heat sink compound

They don't make heat. They are light, so don't absorb much heat. Contact area is large for the thermal mass.

Also they are widely used in products which don't keep a tube of thermal goo around the factory. Coffee makers, furnaces, etc. Only crazy semiconductor dweebs do grease! That's perhaps why they have large area for their thermal.