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In Reply to: RE: Electronic SAFETY when Building, any GUIDE ARTICLES ? posted by drlowmu on August 18, 2014 at 12:20:34
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.
Follow Ups:
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.
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