QUOTE: I have never put fuses in before, I will think about it but don't want to modify the chassis.

Hi

Getting back to the Fuse, the big problem I have is where do you put them?
*If you put them in the HT after the rectifier (Pin 8) then in this case it wouldn't blow.
*Do you put then on the 5V winding that goes to the cathode (Pin 2) of the rectifier. Not sure it would have blown.
*Do you put 2 of them in on the HT winding (Pin 4 and 6) Would have blown one of them and reduced HT, but it was the heater that let go and was starting to short to the HT winding...
*Do you put them on the AC input to the radio and still burn out the transformer....

I guess you could do all of the above but then its modified so much you may as well go with a solid state power supply.......

Food for thought...

Yes, fuses are a problem. It usually takes a sudden catastrophic fault to blow a fuse that's large enough so as to not to fail in service when there's actually no fault. There are many possible faults that can cause a "slow cook" and even a fire without blowing the fuse. Back when I did warranty service on new B&W TVs, an O/C fuse with no other apparent fault was one of the most common reasons for service calls.

The best way to protect a piece of equipment that has a mains transformer is a thermal fuse firmly attached to the lamination stack. Thermal fuses are commonly used in appliances such as clothes driers and could easily be retrofitted to an old radio etc to provide foolproof protection. Very effective peace of mind for old equipment with flammable insulation - paper, wax, pitch etc.

Most small mains transformers these days have integral thermal fuses and use self-extinguishing plastics.

Retrofitting thermal fuses is a damn good idea. It would make a good article for the Vintage Radio section of Silicon Chip.

I would go for the thermal fuse just need a way to attach it to the transformer.

The problem with the black fuse holder is they are meant for 13.8v automotive not 240v. check the rating of them!

Yes, be wary of Jaycar inline holders.

Bulgin makes a range of inline fuse holders rated at 250V.

"Getting back to the Fuse, the big problem I have is where do you put them? "

I favour the secondaries because a fault in the HT circuits or heater circuits may not draw enough power to blow a primary fuse, while burning out the secondary winding.

These fuses can be used for radios used regularly, whereas a radio on display or demonstrated rarely could be protected by operating through the appropriate incandescent light bulb.

Fuses can be constructed with the old fuse wire through a piece of fibreglass spaghetti on a tagstrip and don't look out of place. Always rat failed toasters and kettles - they usually contain some fibregalss spaghetti. They might contain thermal fuses too.

I have found that transformers generally operate about 20-25C above ambient so for 40C ambient about 70-80C rating for a thermal fuse should suit. Any thoughts on this?

Put one of these inside two layers of fibreglass or silicone rubber sleeving, wire in series with mains and glue to the transformer:

https://www.jaycar.com.au/77-c-thermal-fuse/p/ST3800

To be honest I would use this type if I decide to go further. They are 240V rated.

https://www.jaycar.com.au/70-c-thermal-circuit-breaker-switch/p/ST3823

They are 240V rated

So are the fuses part #ST3800, plus they are smaller, thus less intrusive.