Hi Guys,
Since problems that break things consume energy,
has anyone thought about, or have used a thermal fuse
mated to a power transformer with thermal grease?

http://www.jaycar.com.au/productView.asp?ID=ST3804.

I think these ones open permanently, but for $3.50,
if you could save something expensive, it seems worth it,
and also could be hidden in most radios.

They are often referred to as microtemps and I used to replace these in Hoover and Simpson clothes dryers all the time when I was an apprentice electrician.

To be honest I wouldn't worry about fitting these to a radio. Once a power transformer in a valve radio reaches 133 degrees the problem causing the heat will have become acute enough for the transformer to require a rewind. Instead I would calculate the required current flow in the primary winding and just fit the most suitable fast-blow fuse in series with that.

I should also point out that these things are made with varying quality. They are known to blow for no reason and power surges and spikes also destroy them. They are sometimes fitted to toroidal transformers and I simply remove them when this happens only to find that the transformer or whatever the microtemp is fitted to runs satisfactorily for years to come.

I got one of those Jaycar "lucky dip" bags,
and it had a few of them, so I guess I got curious.
I can't see the temp on mine, so the only way to test would be permanently blow them.

I have got a power meter on the radio, that should be handy,
it doesn't cut off though if anything bad happens.

As for the fuse, I suppose when I'm done I could just use the
lowest possible value that doesn't continually blow.
But I have a few changes to do yet, before that value can be determined.

A 150ma or so fuse in the Centre Tap to earth of the HT winding is also a good idea.
But a 2A (or whatever suits) in the Active line is a must have in my opinion

ben