26-08-2015, 04:06 PM
(25-08-2015, 09:27 PM)Murphyv310 Wrote: I've been reading through the thread and an a little worried. You say about safety but I feel that some of the precautions you seem to be taking could actually be a hazard. In one instance you say about using heatshrink over a resistor. This is really silly, the resistor is rated for natural cooling in air, wrapping in heatshrink will cause the resistor to overheat and could result in a fire. Like I've said before try to get the right valve or an equivalent. You'll pull more current off silicon diodes too, a fault downstream could up the current to blow your mains transformer well before you blow a fuse.
It's not totally wrapped. The heat shrink I used is the industrial type and also has a large diameter. It's from the welding shop where I live. Air can still get in but the soldered joints and HT wire is not able to short out to chassis. I also tested the resistor for a while (as well as everything else) and haven't found any sign of appreciable heat. Bear in mind this is a pretty large radio and there's plenty of air and space, plus the resistor is a modern 7 watt. I explained to Maplins what it's use would be.
On the other hand, my small Ultra does get very hot. It's a much smaller Bakelite radio and the tubes are cramped together. I've seen nothing like that kind of heat in my GEC. I don't run the Ultra for too long as it's 1947 and quite small.
However, having said all that, I agree after all this hard work I don't want to take any risks so a proper tube rectifier is probably a good idea. Probably I can get one for a tenner which isn't a King's ransom.
