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Hello,
I am having a musician friend in Canada build his first tube amp. Are there any articles on line, or a books he should read, to advise him of the key SAFETY and safe practices proceedures, when working with tube amps?
Thanks in advance.
Jeff Medwin
Follow Ups:
just for safety on high voltages. Plus all the other stuff that has been suggested here.
Good stuff.
Can you provide us all with a URL to click upon please ?? Thanks
You will have to read through all of the post but there is a lot of info there. It help me out.
Hope this helps!
Looks like he has enough information herein to keep himself safe.
Thanks to all who helped him !!
Jeff Medwin
The ARRL Radio Amateur's Handbook (try to find a pre-1960 edition) has a begenning guide to building techniques and practices.
I was taught to always fuse the incoming AC line and use an inrush current limited (in series with the Hot black conductor in the form of a incandescent light bulb of hefty wattage (> 100watt). On initial turn on, if things are Ok then the bulb will come on and then immediately dim. If things are not OK then the bulb will remain brite. Make sure that chassis are connected to the green ground wire for safety leakage.
Get a rubber mat to stand on when working on a hot chassis. Buy some lineman rubber gloves (like Salisbury) and only work with one hand in the chassis. Buy plastic non conductive tweak tools and insulated hand grip tools. Remember that a high voltage can arc over and jump a small distance.
Discharge all large electrolytic caps with a 5 watt, 10K resistor and rubber insulated alligator clips. These caps can exhibit memory and recharge so keep the resistor connected a reasonable time.
It's also nice to have a bench power supply that is current limited to test circuits.
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
1) It is much less dangerous to build it right the first time. The real danger is in trouble shooting, especially if it must be done with power on. This is where you can help Jeff. Make sure he has a proven schematic. Make sure he breadboards it just like the real layout....no clip leads....the real thing with the same spacing, etc.
2) Know what to expect ahead of time. Have plenty of meters, all hooked up before you apply power. Know what ranges are okay and are not on each one. If you have to wait for smoke, or look at notes, you are courting danger. Again this is where you can help Jeff. He needs to know that some voltages might ramp up before a tube conducts.
3) When you design/build something one should always give thought to what would happen if something fails. It is bad practice to pick cap voltage values with the idea in mind that a tube would present a load and pull B+ down. It doesn't cost that much more to size every cap and resistor for full B+ under no load condition.
4) Keeping the above in mind you do want an protection scheme. You want fuses to blow, and perhaps resistors to go up in smoke. You just need to decide which ones and in what order.
5) Install the extras up front to make mantaining and trouble shooting easy. A panel meter here, some test jacks there, could mean a lot down the road to a beginner. You want to foster his ability to understand basics like tube bias points and balance.
6) If you are going to be involved with picking the schematic and layout....then consider writing a circuit description and trouble shooting procedure. It helps a lot to know what voltages, in what order, and in what places, one should find them. Then info on where to concentrate efforts if one doesn't find them. Poking about in the dark, with B+ on, is a sure way for a newbie to get into trouble. Having to do a good bit of this for work, I can promise you that it will improve your skills to write up such a manual.
So make sure he has a proven plan to work from. Make sure his layout is correct. Blows my mind when I see guys here that don't know which way to count the tube socket pin numbers. Make sure he knows which places to measure when he first turns it on. Probably best to take that in steps....i.e. what ohms to ground on certain pins bfore voltage is applied....what volts to ground with no tubes installed....etc.
Well thought out. Proven schematic???? LMAO, its a FIRST ever built SE DC 6AH4GT amp, first one EVER to be built to my knowledge.
No problem, I designed it uber conservatively, Golden Ratio tube dissipations, 800 VDC WIMA caps for a 415 VDC circuit, ten times over rated low DCR chokes, under ten Ohms each, and I was able to get the Direct Couple to neatly balance out to 1/4 of a volt from a 400 VDC plus supply.
I'm half a Continent away, this musician dude runs A7 ALTECs in Montreal Canada. I'm having a CLOSE communiucation with the fellow, maybe a local friend there to preview the build, and a variac start up. Also have him reading and re-reading THIS thread. Thanks to all who contributed to this thread, a life-saver !!
Jeff Medwin
There are others. Circa 2012, YouTube video.
So I see, I may be the first one to DC the tube in an amp.The YouTube dude says " I was surprised how loud 1 Watt could play. "
Need sensitive speakers !!
Jeff
Edits: 08/22/14
If you are going to suggest something it seems only right that you have first hand positive experience with it. So build the darn thing:) Who knows, maybe it will be prone to oscillations or something sure to cause a first timer grief.
Goes without saying that direct coupled leaves less room for mistakes. Not sure I'd suggest that for a first project.
Workbench safety has little or nothing to do with the integrity of the design. I read a primer on tech safety some years ago, but can't remember where. It included hints like keeping one hand in your pocket when working with live circuits and being careful around a chassis that isn't grounded.
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Buy Chinese. Bury freedom.
It has a lot to do with safety.
1) If I have you build something that I know darn well is going to blow up in your face I think that is a "safety" issuse.
2) If I have you build something that I know isn't going to work right, and make a newbie do a lot of trouble shooting, I think that is a "safety" issuse.
IMHO the best way to insure safety starts with a safely designed item. This is an area I am involved with in the work place. Good work habits go a long ways. Still I see really skilled guys get hurt bad by equipment that is so poorly designed and laid out that "it is an accident waiting to happen". We have seen our fair share of advice given here that would qualify as "stuff waiting to happen".
"...you build something that I know isn't going to work right, and make a newbie do a lot of trouble shooting, I think that is a "safety" issuse."
Sorry, makes no sense to me. The point to all this is to make the newbie an expert at safety. Then it doesn't matter how long he works on it.
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Buy Chinese. Bury freedom.
a
The tubelab piece is good, but pretty wordy. Here are some short rules I follow:
FOR UNPLUGGED TUBE GEAR:
------------------------
Discharge the power supply caps. I use a 100Ω resistor hardwired to high-voltage leads with alligators at one end and a probe at the other. Clip the alligator to the chassis, and touch the probe to each power supply capacitor terminal for a few seconds. It's less dramatic than shorting the p/s caps with a screwdriver. (The screwdriver method works, but will give a big audible pop and spark, and can result in your screwdriver being welded to the capacitor terminal.) Use your multimeter to confirm that the caps are drained.
If you don't do this and get zapped, it is unlikely to injure you, but it does hurt.
FOR ANY GEAR PLUGGED IN, TUBE OR SOLID-STATE:
---------------------------------------------
1. Rubber-soled shoes. No exceptions ever.
2. One hand in your pants pocket. No exceptions ever.
3. Plan what you are going to do before you do it. Don't just start poking about with probes and screwdrivers. If you have to get a probe or screwdriver into a tight spot on a live circuit, rehearse it first with the gear unplugged, one hand in your pocket, and caps discharged so you know you can accomplish what you need to do without shorting out anything (including you.)
4. If in doubt, stop. Put it aside, walk away, clear your head. Come back tomorrow.
WW
"A man need merely light the filaments of his receiving set and the world's greatest artists will perform for him." Alfred N. Goldsmith, RCA, 1922
Good rules! Here are a few more:
I'd suggest using a variac to bring up new projects. You can get them on ebay for a reasonable amount and they can sure help. In the last 20 years I've only made one significant boo-boo and that was somehow connecting the output of a choke directly to ground instead of a cap, as was intended. The variac saved it.
As much as possible I connect meter leads before power up so I can watch what's happening, and that way I'm not poking around a live circuit with a probe that might slip.
I also like to use an analog meter on B+ (a used Simpson 260 is inexpensive and an excellent meter). Watching the needle swing on an analog meter can be very informative and help you spot trouble quicker. Aligator clip leads are handy but be careful if you link them together that you don't then brush against a hot connection.
Variacs are invaluable, cheap, and look cool sitting on the shelf when you're not using them. I always use one to bring up old gear, but admit that when I put a kit together or mod a circuit I generally take a "damn the torpedoes" approach, plug it in and watch for smoke. Haven't had any in the first forty-five years. When I do get some I'll probably just hang up the soldering iron.
I used to use the Heathkit IM-18 VTVM, as it was easy to keep accurately calibrated. It was a good meter, but you have to remember to change the C-cell battery every year or so to prevent having a leaker. These days I use a Fluke 110 rms multimeter, which gives pretty much the same information on its display, including a good LCD approximation of an analog meter movement. It's more expensive, but it includes ac voltage and frequency, dc voltage, audible continuity/diode check, resistance, and capacitance. It's a good tool, and good tools make me happy.
WW
"A man need merely light the filaments of his receiving set and the world's greatest artists will perform for him." Alfred N. Goldsmith, RCA, 1922
I do not have any texts; however EH&S is part of my Job - here at work - a licensed Clinical lab, and Previously I worked building HiFi....
first, I would recommend purchasing a pair of ANSI Z-78 Safety Glasses - that are comfortable - so that you/they will wear them.
Second - there is nothing like a clean work space with room to move and lay out parts, I would also suggest good ventilation as the fumes from soldering (even w/ using lead free solder) are not healthy.
and lastly I would make sure that your friend understands that Capacitors can hold a charge for a LOOOOOONG time - and that the time gets longer the bigger the cap.....
Happy building
the transfer function will not be sufficient to completely kill him. Make sure he uses two runs for beginners safety. Once he passes this hurdle he will be ready for the full three runs and he can graduate from mid-fi to deadly audiophillia.
...........forgive them; for they know not what they do.
Jeff,
Here's an example I found a while back...
http://tubelab.com/safety/electrical-safety/
Respect coupled with knowledge...I've been lucky on a couple of occasions.
Stuben
~!
The Mind has No Firewall~ U.S. Army War College.
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