Hi guys,
I begun working on electronics on my own shop back in 1989; it was a tv set repair; many tube units were still being repaired at that time. They were the worst thing to put your hands on; live chassis, +B of around 300V, and crt HT of 25KV. One day I remember I flipped one tv set on one of its sides and separated a few centimeters the chassis from the tv case to make some meassurements on the backplane, I was sliding my forearm in carefully with one multimeter probe in my hand when accidentally I touched some +B spot; went catatonic for a few minutes until I realized I was still alive. That was the first and only time I had such a huge voltage shot. Learned the leason the hard way.
Later on worked for siemens in the electromedical division, on X-ray and CT scanners. They were very emphatic at the training courses in germany about the hot spots where if you touch you go.
I begun working on electronics on my own shop back in 1989; it was a tv set repair; many tube units were still being repaired at that time. They were the worst thing to put your hands on; live chassis, +B of around 300V, and crt HT of 25KV. One day I remember I flipped one tv set on one of its sides and separated a few centimeters the chassis from the tv case to make some meassurements on the backplane, I was sliding my forearm in carefully with one multimeter probe in my hand when accidentally I touched some +B spot; went catatonic for a few minutes until I realized I was still alive. That was the first and only time I had such a huge voltage shot. Learned the leason the hard way.
Later on worked for siemens in the electromedical division, on X-ray and CT scanners. They were very emphatic at the training courses in germany about the hot spots where if you touch you go.
Do you try and cope with the wide range of DCV that could be deemed hazardous (eg. 50 to 500V) ?
The LED does stay on (but dimmer) as the voltage dies away.
By the time it I has gone out it is pretty safe to touch.
I got new Valvo EL84 tubes from Germany yesterday. When I put them in the amp it started to pop like crazy in the Radian 2" compression driver! I remember seing rust on the staples on the tube boxes, and then I noticed champagne coloured oxidation on the EL84 pins. They must have been stored in a moist environment over in Germany.
So I took out my trusty Dremel tool and started grinding down the pins until I saw bare, shiny metal. That solved it. Sound improved as well. The connection must have improved a lot.
I will do this a safety precaution on my other amps as well, since it may also improve sound quality.
One time a tube preamp lost connection to the tube pins and it burned through a resistor on my $640 Lynx soundcard. Had to send the Lynx across the Atlantic for service. Never dared to use the preamp again. I use a passive preamp with a step attenuator now - very clean sound.
So I took out my trusty Dremel tool and started grinding down the pins until I saw bare, shiny metal. That solved it. Sound improved as well. The connection must have improved a lot.
I will do this a safety precaution on my other amps as well, since it may also improve sound quality.
One time a tube preamp lost connection to the tube pins and it burned through a resistor on my $640 Lynx soundcard. Had to send the Lynx across the Atlantic for service. Never dared to use the preamp again. I use a passive preamp with a step attenuator now - very clean sound.
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Be careful that you aren't creating minute cracks in the glass base. Annealed tube glass cracks very easily under stress. My favourite is a small brass brush on a model drill, no more.
richy
Yeees, I should maybe have been more careful. Everything sounds good here tho.
Just something might be of interest,
Thoughts from another thread.
Another reason to use discharge resistors, if the B+ is up for weeks after power off. That's when little fingers go to work pushing hair clips into the vent holes. Doing what daddy or mommy does with their hobby!
Regards
M. Gregg
Thoughts from another thread.
Another reason to use discharge resistors, if the B+ is up for weeks after power off. That's when little fingers go to work pushing hair clips into the vent holes. Doing what daddy or mommy does with their hobby!
Regards
M. Gregg
"Salute, Genius!"
Water conducts electricity!
An externally hosted image should be here but it was not working when we last tested it.
Water conducts electricity!
Matt and all others use rust REMOVER in future it is safer than grinding those slender tube pins even aluminium
Whatever chemicals you use instead of a dremel tool must damn strong. I had to cover the same area with the grinder three times to get a shiny surface on these vintage tubes. I think buying cheaper tubes and get good contact is better than buying hyped tubes for a hundred bucks and not dare to touch them.
MDF contain formaldehyde, which is classed possibly a carcinogen by the WHO. This applies to the dust, but also the formaldehyde gas that keep oozing out during the lifetime of the speaker. The gas can be trapped with the right kind of paint. Oil based paints were less effective in trapping the gas. The dust is also very allergenic. Knowing this I am trying to stick to as much natural wood as possible, when building speakers and horns.
Well, I have seen a lot of very good safety tips:
Always assume the circuit is hot, unless you have measured it,
Use proper tools,
Don't go fooling around if you're oblivious about the risks,
Don't get cocky, kid,
Get help from a pro if you can,
etc.
But how about:
Think about what you're wearing (a woolen or fleece sweater CAN fry your electronics, or you if you have bad luck).
And one not a lot of people'll think about, but an important one I've learned in basic training:
GET ENOUGH SLEEP! You can do some types of work if you've spent the previous night patrolling, training, partying, gaming, watching a LOTR/Star wars/Star Trek/Grand Designs/anime marathon, designing/drawing a kick-*** amp, listening to Bach/Tchaikovsky/etc. or what ever, but that will be severely limited to work you don't have to have a clear head.
You WILL make mistakes if you've not had enough sleep, and that will get you a ride to the ER or morgue if you're working with lethal systems/voltages/chemicals/tools/equipment/heavy machinery etc.
Always assume the circuit is hot, unless you have measured it,
Use proper tools,
Don't go fooling around if you're oblivious about the risks,
Don't get cocky, kid,
Get help from a pro if you can,
etc.
But how about:
Think about what you're wearing (a woolen or fleece sweater CAN fry your electronics, or you if you have bad luck).
And one not a lot of people'll think about, but an important one I've learned in basic training:
GET ENOUGH SLEEP! You can do some types of work if you've spent the previous night patrolling, training, partying, gaming, watching a LOTR/Star wars/Star Trek/Grand Designs/anime marathon, designing/drawing a kick-*** amp, listening to Bach/Tchaikovsky/etc. or what ever, but that will be severely limited to work you don't have to have a clear head.
You WILL make mistakes if you've not had enough sleep, and that will get you a ride to the ER or morgue if you're working with lethal systems/voltages/chemicals/tools/equipment/heavy machinery etc.
Hello to all of you.......Something more as regards safety....
Have one of your hands in your pocket when you do measurements and adjustments on a live circuit.
Do not step on the floor without shoes.
Use well insulated probe leads.
Keep your mind in what you are doing and think twice before you take any action.
Make sure you have unplugged the equipment before you put your hands inside the unit.
Place a sign near the equipment to remind you that lethal voltages are involved " Attention !!!! Death hazard!!! This unit operates at 5000V !!! Death is permanent !!!
If you have to work alone pay double attention.
Hope that everything would be fine
Take care!
Have one of your hands in your pocket when you do measurements and adjustments on a live circuit.
Do not step on the floor without shoes.
Use well insulated probe leads.
Keep your mind in what you are doing and think twice before you take any action.
Make sure you have unplugged the equipment before you put your hands inside the unit.
Place a sign near the equipment to remind you that lethal voltages are involved " Attention !!!! Death hazard!!! This unit operates at 5000V !!! Death is permanent !!!
If you have to work alone pay double attention.
Hope that everything would be fine
Take care!
Just what I was going to post.
I often get ideas late at night after mulling over a topic all day or so.
-If you are middle-aged, don't work when tired.
-If it is past 800pm, I don't work on it. I get some sleep and do it the next day.
-I make notes and do it the following morning after a cup of coffee.
-Have GFCI/RCD (Ground-Fault Circuit Interrupt/Residual-Current Device), Ground Fault, Ground Lifter on your workbench line.
-One hand in the chassis at a time.
-Always pull the plug and treble check it, put it in the middle of the work area to see that it is not plugged in. Clear uncluttered work area so it's obvious that one plug goes to that one chassis.
-Bleed the HV line, caps and transformers, with resistors and measure it with a meter before working on it.
-Having a friend or family member around when tinkering is best, just in case, but this hobby is often solitary so this suggestion will be impractical for most of us.
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In a new but rather low-remunerating job I am doing QA on control panels with PLCs and VFDs on them. There is usually a cabinet and the power per VFD is up to 20HP so far. I am just working on the smaller units.
The typical voltage is 460V 3 phase. The supply to the test station is 30A through breakers. After a month of this, I find myself getting a bit accustomed to it, as I have done wit the higher DC voltages in the home built stuff I work with.
Complacency is extremely dangerous and this is the reason why there are not only safety rules but definite procedures when 'breaking the plane'. That is defined as the plane of the otherwise closed door of the cabinet.
The same consideration should be given to the underside of the chassis of tube equipment. There is really no telling when a 300-400VDC circuit will give only a nasty shock and when it ill be deadly.
The typical voltage is 460V 3 phase. The supply to the test station is 30A through breakers. After a month of this, I find myself getting a bit accustomed to it, as I have done wit the higher DC voltages in the home built stuff I work with.
Complacency is extremely dangerous and this is the reason why there are not only safety rules but definite procedures when 'breaking the plane'. That is defined as the plane of the otherwise closed door of the cabinet.
The same consideration should be given to the underside of the chassis of tube equipment. There is really no telling when a 300-400VDC circuit will give only a nasty shock and when it ill be deadly.