18Watt.com

If you are taking an old valve apart, it is almost certain to have some thorium on the cathode. Now, under EEC regulations it is permitted to possess less than 0.45g of thorium (as nitrate) without requiring a licence for radioactive materials - so it is not a big risk, but it is a real risk. Putting it into English, if you take one or two valves to pieces you are not likely to damage yourself unless you suck the cathode element - but unless you are wearing a radiation telltale badge, you have no way of knowing. Your risk ...

good lord my man, you could take these things apart all day long.
i know that i did at age eight. now i have T3 prostrate cancer. is it realated?
you be the judge. my advice? leave the insides alone

Wow, that freaked me out. You have never seen someone spit out a cathode element as fast as I just did.

dotfret wrote:If you are taking an old valve apart, it is almost certain to have some thorium on the cathode.

Are you absolutely sure of that? AFAIK thorium is only used in directly heated valves that operate with very high filament temperatures - ie the kind that light up like 200W bulbs.

Radio active amp! That sounds cool.
Can it have a big knob just like the one out of back to the future part 1.
Oh, and a single 24" speaker.

Groundpath wrote:Wow, that freaked me out. You have never seen someone spit out a cathode element as fast as I just did.

I guess that's another reason to not drop your amp. If all the tubes in your 4 channel monster cracked then you might start glowing in the dark! Think of the damage an SVT could do!

I doubt if the tiny amount of thorium on the cathodes would cause prostate cancer - but if one were habitually dismantling alarm clocks as well as valves, I could see that the luminous paint on the dials might contribute, if there were lots of them - but that is radium, not thorium. Face it, there were lots of radioactive materials employed in past times - uranium mining waste was sold as a fertiliser about 100 years ago in England, and although I collect pottery I will not buy anything orange from the 1930s era because it is likely to be a uranium based colour - try a Geiger counter on your Clarice Cliffe stuff!
I might add that I invented the phosphate-silicate cement which is the basis of prostate cancer palliative implants, and I have worked on cancer cure drugs, so I do have a clue on this matter. What I was saying is that the few mg of thorium in the cathode coating of a set of valves is probably quite tolerable to the average human - and that even with a big set (like the SVT) it should not be a problem. It does remind me of an advert that used to appear in the Melody Maker in the 70s -
"Break out my Accoustic amp and stack, Mr Spock, I wish to boldly go"
"Right away, Captain"
"Och, Captain, the crystals winnae stand it!"
It is not true that thorium is only used on directly heated cathodes, Phil - it is true that most of the documented research relates to using thorium on directly heated cathodes. Thorium is incorporated in almost every manufacturer's special brew cathode coating from the 30s up. Some valves use an alloy of tungsten and thorium, as well as the thorium (and barium) in the coating. Most of the real secrets of the old valve makers were regarded as trade secrets, never to be public knowledge or revealed via patents. That is why we are unlikely to discover the secrets of the Blackburn processes, why they were so different from other valves of similar design within the European organisation. Sound-wise, I have to say that I have tried a lot of valves in a lot of amps, and I like Mullards a lot - but the fat boy EL34 tubes beat Mullards for high voltage handling, and I prefer VERY old RCA 12AX7 valves for sheer tone over the yellow label Mullards that I am using habitually - but the amps I use do not test the voltage handling of the valves. I have four amps with 2 x EF86 into a 12AX7 into 2x EL34 - these give me a definitive Brit blues sound, which I stick with. They are all "kind" designs, in that they do not over-tax the valves, or push them to their design limits. I am so fond of these amps, it only ocurred to me recently that I haven't even powered up most of my other "collector special" amps for about 20 years. Got to do it ...