Touching tubes with fingers

[galaxy95Tman]

Just wondering if touching tubes with your fingers really does shorten the life of them?

[KG4KGW]

No it doesn't. The oil from your fingers creates a hot spot on the glass that in some cases could cause the envelope to fail. I've never seen it happen, EVER. I'm sure there is someone out there that has. This is the same principle as a halogen lamp. It's just good practice to keep your hands off the tubes and keep them clean. Not to mention every time you handle the tube you are causing vibration that works to damage the junctions within the tube. This isn't really any worse that turning the power on or off. Inrush current does far more damage to tubes than touching them with your fingers.

If you want to learn more about how to prevent inrush current try doing a search for amplifier soft start circuits.

['Doc]

The most dangerous thing about any tube isn't that the tube will fail, but that YOU might. Depending on the tube, they get hot, they have higher voltage applied to them, and they are made from glass (most of them). Any of those things can 'bite' you if you're not careful. I can't remember any tube I've used that's failed because I touched them. But, I've seen tubes fail because of other reasons and have had to use gloves to get the @#$ thing out of the socket. Just a good idea not to go around touching things without being careful (not just tubes either).
- 'Doc

[KG4KGW]

Doc has a very important point that I didn't even think to mention. There is some very dangerous voltages around tube equipment even when it has been off and stored for years in some cases.

Not all equipment has bleeder resistors to take the HV to ground when it is not in use.

Case in point is an amplifier I had here at the house. It had sat in a closet for about 2 years (Yes I know this isn't good for tubes). I was fishing a piece of cable through the cabinet and laid my arm across the anode of the tube while touching the cabinet at the same time. This amp discharged 2 very large 4MFD caps into me! It took my legs out from under me. I was lucky. I knew better than to trust HV equipment and I had a hand in my back pocket. Had I been leaning across with my arm other hand on the case it could have killed me easily. It isn't voltage that kills...it's the amps that get you!

Now I make sure everything is discharged before I even think about touching it, even with one hand. This means more than just turning it off and waiting for a few minutes. There are devices used to discharge things like this, often called "chicken sticks". These can save your life.

The amplifier that I was working with when powered up has 2500V on the secondary. This goes through a large full wave diode stack and then to a pair of oil filled caps before going on the the amplifier from the power supply. I have no idea how much energy was stored in those old caps, but I can say it hurt for days.

Like Doc said, if it is in circuit DO NOT TOUCH IT! Amplifiers should have safety interlocks to prevent tampering while they are on and bleeder resistors to take them back to ground when they are off. Adjustments should only be made by someone with intimate knowledge of the working circuit and experience with high voltage. You can never give these things enough respect.

[MDYoungblood]

I believe in wearing gloves, bare hands on a stuck tube, the glass is thin and easily broke, not only would you have to find band aids but clean the blood out of the radio, blood is conductive. As a kid I worked for a Electronics Repair Shop, did mainly TV's but worked on everything, had a tech almost take off a finger in a TV, took days of washing it out with distilled water to get it back to working.

3's

Greg

[dirtyjob]

i grab em all the time, never had an issue, i would however advise anyone with tube equipment to unplug and then turn the power switch ON to drain the caps before monkeying around inside, I have been BELTED in my time from a cap discharge and its not pleasant.

[MDYoungblood]

After reading these posts I have come to the concussion that you should take it to someone that knows what they are doing. If you want to play around inside equipment with high voltages, have a loved one take a First Aid/ CPR course and maybe if you can afford it buy a AED, lol.

73

Greg

[galaxy95Tman]

Thanks everyone for all the great info and replies. I'm always very careful and discharge everything with a chicken stick. I've been messing around with radios for 30 years and I'm no tech or expert by far but there are a lot of knowledgeable people on here that help the rest of us continue learning and enjoying the hobby ever more!!