Seeking Valves

[Nowhere-Man]

Like Tevor, I too am worried. Heatshrink over a high power reisstor is a very bad idea. If the resistor gets really hot as they are designed to do the heatshrink won't survive. At best there will just be a nasty smell, at worst it may not be as flameproof as you hoped.

Fuses look simple but are a complicated subject. A 1 amp fuse doesn't blow at 1.1 amp. The more current you take, the quicker it blows. This page will tell you a lot more than you need to know: http://wiki.diyfaq.org.uk/index.php?title=Fuse The important point is that fuses will not protect against small, long term, overcurrent.

In many cases there's no problem if you replace a valve rectifier with silicon diode(s) and a resistor. Yes it can stress the capacitors in the set more than a valve because full HT is available immediately power is switched on and before the valves start to conduct and drag the HT down a bit. Yes you can get higher curernts through silicon under fault conditions. Thes are often acceptable risks. We're here to help you make sensible judgements.

You've clearly been struggling a bit with soldering. We all had to start somewhere and I'm sure most of us made a hash of it at first. Presented with a crowded chassis, wires wound round tagstrips and old solder it can be tricky to do a good job. It can be hard to melt the solder at all at first. One trick is to run a small amount of new solder between the iron and the old joint. Once the old joint is fully molten you can use a solder sucker to get rid of a lot of the old solder. To save disturbing a possibly delicate tag such as on a valveholder you can remove a component by cutting its leads near the body of the component. Since modern repalcements are usually smaller it's then quite easy to join thenew component to the old leads. The purists can make some very neat mechanical joints between new and old leads. I'm not a purist

As I said earlier, we all had to start somewhere and we've all made mistakes. Those of us who are still here obviously didn't make any fatal ones We like to help those who are less experienced but it can be hard to do it from verbal descriptions and even from photos. There's nothing like learning directly from somebody with experience sitting next to you but this isn't always possible.

O.K. a few words about heat-shrink and resistors as today I tried out a simple experiment. Before I continue, I'd also like to say I agree with your comments on fuses. I did fit 2 amp fuses to all my radios and I agree it does provide some safety yet no guarantee. While I was at it, I wired in an RCD closer to my supply and that should trip out at 0.03 amp.

Now, here's what I did with the heat shrink. The results are open to debate: The stuff I used is quality industrial shrink. Basically I loosely wrapped the upper bar of my soldering iron with this shrink and switched on. I allowed the iron to get extremely hot. And I mean, hot. I then unplugged the iron and allowed to cool a bit. I carefully scraped and removed the heat shrink from the iron. It was way too hot to touch. There was no sign of smoulder, blackening or burning.

Therefore, it would see any danger would have to relate to the actual resistor body and not the shrink. On that score, I really have no idea. I can only assume if the resistor heated up internally due to lack of air around the body, there would be an issue. If anyone knows specifically any heat stats for these ceramic resistors I.e. internal heat tolerances, I'd be interested to know. How do they compare with vintage resistors? I've seen damaged resistors due to heat and have replaced them at times.

And to put minds at ease, I did decide it would be a good idea to allow full air to get to the resistor body, just to be safe and cautious. I'll do that tomorrow. I did today run the radio for a while and I took the temps of the resistor. It was hot but nothing comparable by any standards to the soldering iron test temps. As I say, I simply don't know whether there are risks of internal heat within the body of the component itself. All I can say is if the body of the resistor got way too hot, the heat-shrink wouldn't burn but maybe the resistor could itself be damaged.

I don't ever run my valve radios unsupervised. I enjoy using a 1947 Ultra at nights on my boat but I'd never go off the boat and leave it on (or even plugged in). Even despite my best efforts, it's still a Forties set and very old.