Phil Allison wrote:
"Gareth Magennis"
"Phil Allison"
I understand they work on bi-metal strips.


** Nope - that is a temperature switch.

Thermal fuses like this one use the melting point of some material and
rely on a spring to open the circuit.

http://media.digikey.com/photos/Cant...1%20DF100S.jpg


This is the type Peavey have hidden in the mains transformer of the
Classic
30.

** Eeee - yep.

I only discovered it by accident when I decided to dissect an "open
circuit"
one, no mention in the schematics AFAIK.

The owner had had 2 mains transformers replaced previously, seems, from
Googling, these transformers are woefully underpowered and often break.
Wonder if the only failing part is actually this switch?


** We must be leading parallel lives ..........

I actually have a power tranny from a PV Classic 30 in my used parts bin.

The thermal fuse was open - it resembled the one in my pic.

I replaced it with a new one of slightly higher temp rating and it works
fine.

The customer got a new tranny, as requested.



... Phil

Hi,
I fiddle with guitar amps. Son is into playing guitar/bass and drum.
Have a crude set up for recording as well. Have some vintage Marshall,
Fender, Boogie amp. Guytron and Soldano. Hugh & Kettner. Built couple
Fender clone and Marshall JMP clone from mono tube amp. Let kids blind
test it placing it side-by-side with real thing. They couldn't tell the
difference.