Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: drgonzonm on March 23, 2017, 04:22:29 pm
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I am curious, has any one considered using the power cord off a hair dryer as the power cord for an amp? Or a power cord for a vintage valve saver?
The hair dryers sold in my area come with what I believe are GFIs, This offers protection on a two prong plug, that is not normally offered. I remember a discussion on this forum regarding protecting players and amps in Japan.
And of course some of us live in houses where two prong plugs are the norm.
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I use amps with 2 prong. Think nothing of it. I simply check the outlet. My 64 super and 66 marshall will never have them. I do not advocate anyone else doing the same but in the panel in my home neutral and earth buss are the same thing.
It is the places we play where where club owners and hack electricians cannot tell black from white. In a club in east atlanta checking outlets and found a regular outlet read 240. Each leg to ground was indeed 120.
My point being your safety is up to you.
Anyone else feel like fishing🤡
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I thought GFCI's require an earth and trip if they detect too much going to earth instead of between the hot and neutral, so therefore it can't work with 2 prongs. basically, like Ed said, it's a crapshoot, if you're in a place with really shoddy wiring, you're playing russian roulette. Best to have the three prongs if at all possible. I do recall someone mentioning they found some 3 pronged cords that were as skinny as the 2 prong ones so they fit in those old chassis' without needing to drill the hole larger. I myself wouldn't ever hesitate to drill a chassis to make it safer, but would obviously ask anyone wanting me to make a change to their amp, and highly recommend it.
~Phil
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GFCI's reference the neutral side. That allows you to use them in two wire conditions in bathrooms, kitchens, basements, garages, exterior, etc... It is required that you put a "No Equipment Ground" sticker on them. As Ed said, reverse polarity and 240v misswires are bigger issues.
Jim
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GFCI's reference the neutral side. That allows you to use them in two wire conditions in bathrooms, kitchens, basements, garages, exterior, etc... It is required that you put a "No Equipment Ground" sticker on them. As Ed said, reverse polarity and 240v misswires are bigger issues.
Jim
Oh interesting, gotcha. Thanks!
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> I thought GFCI's require an earth
No. (LOOK at your hair-dryer.)
> trip if they detect too much going to earth
They count the electrons going out the black wire and coming back on the white wire (whatever the two current-carrying wire colors are). If the two counts are not exactly the same (few-mA difference), it knows current is going somewhere else (ground or other!) and *assumes* the current may be going through a precious human.
This may save your life.
It does NOT address the lesser problem: high-gain audio systems hum/buzz unless the audio common is somehow referenced to the electric field in the room. This may not have to be a "solid" ground; however it usually wants to be solid-enough to give a real shock. This was the idea of a 0.05uFd cap to one of the two pins. In days of no seatbelts, leaded gas, and unfiltered cigarettes, 0.05uFd to 117V was not the biggest risk of the day. But people DID die (especially when this cap went short), so we no longer do this.
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There were older shock-protections (especially in the UK) which did measure ground current. These were easily fooled due to the many possible sneak and surge paths.
Most recent US 3-wire GFIs do include Green in a secondary level of protection. White and Green should connect ONLY "back in the fusebox" (many special cases, see NEC). If a GFI detects that White and Green seem to connect "very nearby", it will trip. I observed this without understanding when I kept tripping a GFI in testing. I had an actual problem with the outlet I put right next to my fusebox (2 foot cable); running the cable up and back (say 6 feet) and trying a different GFI "fixed" it.
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Prevents the "Upgraded wiring!" statement from the flipper on the house from 1902 with knob and tube. Will not work on GFCI's with ground and neutral tied together at outlet to give the impression of a grounded system. Other "grounded" outlets however, require a little more sleuthing....
That is odd because many GFCI outlets are mounted directly onto main panels where the grounds and neutrals are bonded - literally inches away. Maybe an extra sensitive one? Rule of thumb neutrals and grounds need to be bonded in panel of main disconnect. Not in sub panels, not in main panels with remote disconnect (such as at meter base or in garage for the fireman). Pools and spas are a different story as they must also be bonded to a ground rod at the electrical appliance (pumps, heaters, etc). Pools also need special grounding schemes. Docks, etc, etc, etc.... As PRR said, see NEC for an absolutely gray interpretation! See Mike Holt for some clarity.
Jim
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I know Knob and Tube, have it here at my house, we pulled it out of two rooms but still have it in a hallway, I need to finish up that job :P (I've heard say that it's actually way safer than the way we do it nowadays but the wire was rated for 10A and nowadays everyone wants 15-20A circuits and if some dumbass patches the K&T into a 20A circuit it's not going to go well.
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There were older shock-protections (especially in the UK) which did measure ground current. These were easily fooled due to the many possible sneak and surge paths.
Most recent US 3-wire GFIs do include Green in a secondary level of protection. White and Green should connect ONLY "back in the fusebox" (many special cases, see NEC). If a GFI detects that White and Green seem to connect "very nearby", it will trip. I observed this without understanding when I kept tripping a GFI in testing. I had an actual problem with the outlet I put right next to my fusebox (2 foot cable); running the cable up and back (say 6 feet) and trying a different GFI "fixed" it.
I will accept that distance may be a factor on some GFI's. My experience with GFI's, began, when you found GFI's in the panel box, not at the outlet. (Outlet GFI's cheaper). Distance definitely less than 2 ft. But it wasn't so long ago, I put a 277/120-0-120 transformer one one leg of wye system 480/277 (60 HP) pump motor control center. We provided three plugs, a 240, and two 120s. (application is very similar to wiring a PT with a CT) The owner wanted to run a small 1 hp pump in the area for various reasons. Even after 3 visits, The journeyman electrician could not wire the GFI's correctly. (He wired a floating neutral). We corrected his wiring by wiring the neutral to ground at the same lug as the green/yellow-green wire. His boss also a journeyman, would not ok grounding the CT of the transformer to ground. It took several phone calls and several days including calls to the local electrical inspectors to get the transformer wired properly. (Instructions did not label the CT point as a CT) The local inspectors wanted the CT point labeled as a CT. Finally got the manufacturer of transformer to supply a schematic showing a CT.
Regarding miswiring, with the same electrical contractor, we bid on a job to provide wiring within a building with three phase power. Only the 10 ton ac was three phase. The electrical engineer called for a wye system. We completed the wiring, provided some plugs for other contractors to do their work. some of the plugs were 208 to ground. Had we completed all the plug installations 1/3 of the plugs would have been 208 to ground. The local power company provided delta three phase. :cussing: The mechanical contractor had to replace an $800 board at his cost, and we lost three cordless battery chargers.
The owner also had to pay for a subpanel so the required 120 plugs could be provided. (We also wired the electric water heater 208v instead of 240 volts).
With a pool contractor, we had an electrical inspector insist that we ground the electro-potential ground to the main panel ground. We refused, got a red tag, and an apology a week later from the inspector's boss.
Playing with electrons can be fun as well as deadly.
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I know Knob and Tube, have it here at my house, we pulled it out of two rooms but still have it in a hallway, I need to finish up that job :P (I've heard say that it's actually way safer than the way we do it nowadays but the wire was rated for 10A and nowadays everyone wants 15-20A circuits and if some dumbass patches the K&T into a 20A circuit it's not going to go well.
What size is the knob and tube wire?
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I don't remember, did it 3 years ago :P
~Phil
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> What size is the knob and tube wire?
It can be more a question of insulation. Ceramic knobs do not care, but K&T systems often had cotton sleeving "loom" where they went too close to pipes or ran through walls.
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my art studio/bedroom is the only room left tube n knob, I leave it because it's a great attic mouse trap :icon_biggrin:
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I'll just stick with my usual 3-wire power cords. Thanks.
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Talk about knob and tube, my 17 room, 1873 farmhouse was filled with knob and tube when I bought it in 1985. And let me tell you it's dangerous. I replaced all of it but during the re-wire I found a single hot wire under the floor pulled tight against an old 100 year old joist beam so tight the the cloth was disintegrated and the bare wire was pulled tight against that beam. Lucky it was only supplying a 120v light bulb. Had I plugged in an air conditioner on that circuit that wire could have gotten hot, probably red hot as the fuses were 20 amp, wire was 14 gauge.
I got shocked too once, thought if the breaker was off on a circuit you'd be ok, well back in the day they tapped the neutral in that circuit for another circuit which was running an air conditioner. I got the sh*t shocked out of me as the return current was running back through that neutral. Get that stuff out, all of it.
al
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thought if the breaker was off on a circuit you'd be ok,
Been there!
I bought my place in '91, the owners had put in a brand new 150A mains, with 4 breakers!
when I was looking in the attic, under all the 2 wire (bare wire) runs were little bones, when my wife asked "how does it look?", I just smiled and said, "shouldn't be a problem". The box is now full, I have a 100A sub, and 2 60A sub, but for history's sake I left 1 run, ~ 30ft, tube and knob.