Mystery part Peavey Solo Series Bandit 112

[Stratfordade]

I’m servicing a circa 1989 Peavey Bandit. I love the quality and sound of these amps though they seem pretty overlooked by the used market. Absolute pleasure to work on - the solder joints all still shiny and good after 35 years.

There’s a component between the two output power transistors that puzzles me. What could it be? It’s inline with the power switch and power transformer primary but don’t think it’s a fuse.though it measures as almost a dead short. The two wires back to the switch/primary are carried in a clear sheath crossing over half the board. One side is bolted to the heatsink but for some reason it’s riveted to it on the other side so not intended to be replaced!

Can’t see it on schematic as I’m in UK and the schematic is for US model with a ground lift switch in that area which is omitted from the amps sold here.

It’s not part of my troubleshooting but I’m just curious about what it could be? Any ideas?

Thanks

[x-pro]

Thermal fuse. It may be self-returning.

[Stratfordade]

Ah I see. Thank you!

[g1]

Yes, it's a thermal breaker and self-resetting. Some of them cut out the AC primary, some of them cut out the line to the speaker.
In the schematic attached, it is called out as 'TB1' for the 120V version, and by part number in the 240V version.

[Jon Snell]

It is known as a Bimetalic Thermostat. Never had one fail.
Here is an example;
https://www.ebay.co.uk/itm/286154373...Bk9SR-rz2_mIZQ

[Pixel]

I saw this part in an amp for the first time last month when I was working on a Peavey Express. I have seen it lots of times before though...in coffeemakers.

[Mick Bailey]

Even late 60s Vox SS amps had them.

[J M Fahey]

I saw this part in an amp for the first time last month when I was working on a Peavey Express. I have seen it lots of times before though...in coffeemakers.

Beeing in Argentina, most parts are available here ... IF some importer thinks he will sell them.quickly.

So normal parts? Popular/standard transistors/ICs/caps, etc.? No big problem.

Specialized/niche parts? Big PITA.

Ordering from US is not an option, since for any Import operation I pay a fixed "base" cost of about $60, crazy. (Canadians complain about some $12 minimum cost , multiply it by 5X to really feel the pain).So I heve to make do with whatever is commercially available, already here.

So big "metallic fried egg" thermostats are hard to find, now coffee maker parts are available everywhere, dirt cheap..
So coffeemaker thermostats it is, I had to make a small bent aluminum clamp to hold them in place, plus a drop of silicone grease for better contact.

OR I had to use pressing iron type ones.

Easy to find, problem is they are big and clumsy, but advantage is they are fully adjustable, which is a big bonus.

[g1]

Also sometimes used in power amps to switch fans to higher speed setting. And available in normally-open and normally-closed versions of switch.

[J M Fahey]

Yes, Fender does that in some amps.
Better than nothing.

[Stratfordade]

Yes, it's a thermal breaker and self-resetting. Some of them cut out the AC primary, some of them cut out the line to the speaker.
In the schematic attached, it is called out as 'TB1' for the 120V version, and by part number in the 240V version.

Stupid of me. I had same schematic and just saw the fuse symbol without spotting one labelled ‘TB’. Thermal Breaker. Doh!