Odd wiring in tube ampmschematics

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I would post this in the basics group but it seems like there are more
responders here. Anyway, I have been looking at DIY single ended tube
amp schematics recently. These are modern schematics using grounded
power cords. And several have in common that the power switch is in
the neutral line and the fuse in the hot. Wouldn't it be safer to have
both the switch and fuse in the hot line?
Thanks,
Eric

Re: Odd wiring in tube ampmschematics
On 2018/12/06 10:04 AM, snipped-for-privacy@whidbey.com wrote:
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For a 3 wire power system (with grounded chassis) that is incorrect as  
you suspect.

For a two wire power then it is correct to have the switch on one side  
of the line and the fuse on the other as you don't know (unless the plug  
is polarized) which side is hot when plugged in.

John :-#)#

--  
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
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Re: Odd wiring in tube ampmschematics
wrote:

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Ahh, that makes sense. I bet a lot of the designs copied existing
older circuits where possible.
Thanks,
Eric

Re: Odd wiring in tube ampmschematics
On Thursday, December 6, 2018 at 2:37:02 PM UTC-5, John Robertson wrote:

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There is that. I tend to replace line cords with those using polarized plugs, if possible, and then keep the fuse (if any) and switch on the 'hot' line.  

General, I would not add a fuse to an AA5, but rather use a purpose-made fused box, plugging the radio into that. In such a way, the fuse level could be varied, and the hot will surely be fused in any case. '

The problem with converting old amps to 3-wires is a matter of hum-loops. Just don't do it. Polarizing the plug is fine. There is a very long explanation of why this is so, but "hum loop" should be enough.  

But, at no time with a repaired/restored amp should power exist on the transformer or chassis with the power switch in the "OFF" position. Full Stop.  

Peter Wieck
Melrose Park, PA  

Re: Odd wiring in tube ampmschematics
snipped-for-privacy@flippers.com says...
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I am getting into this late.  

When replacing the line cord on an older 2 wire cord ( no ground) with a  
3 wire grounded cord, which is the perferred method ?  Go from the hot  
wire to the switch or the fuse first, then to the other and transfromer  
, back to neutral ?  Of course the grounded pin on the plug goes to the  
chassis and the 120 VAC is isolated from the chassis by the transformer.

Several of us were discussing this the other day, but none of us knew  
for sure which should come first, switch or fuse in the 3 wire 120 vac  
equipment.
  

It did seem that in the older ARRL Handbook the 2 wire cords had the  
fuse on one side and the switch on the other side of the transformer.




Re: Odd wiring in tube ampmschematics
On Thursday, 6 December 2018 22:03:43 UTC, Ralph Mowery  wrote:
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Fuse & switch should both be on the live side. Fuse should come first, switches do sometimes short. Wires to switches can also come adrift.


NT

Re: Odd wiring in tube ampmschematics
On 6-12-2018 23:03, Ralph Mowery wrote:
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A 2-pole switch would be the first thing I would add.

Re: Odd wiring in tube ampmschematics
Ralph Mowery wrote:
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** I would opt for switch first, then fuse.  

This is for the benefit of silly owners who like to swap back panel AC fuses while the item is plugged in  -  relying on the switch to isolate both ends contacts on the fuse holder.  

Something that needs to be checked, cos only some fuse holders do this.  






Re: Odd wiring in tube ampmschematics
On Thursday, 6 December 2018 17:59:08 UTC, snipped-for-privacy@whidbey.com  wrote:
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You're right, that is obsolete practice from the days of unpolarised ungrounded power cords. I don't think it ever had any advantage from a safety perspective, it was just fractionally easier to terminate the mains cord onto a switch & a fuse.


NT

Re: Odd wiring in tube ampmschematics
Maybe your wall plus is not respecting the norm.

So, what you call neutral might the the phase line.

To comply to safety rules, manufacturers must protect the phase line,  
not the neutral (VDE, UV, IEC, ANSI...).


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Re: Odd wiring in tube ampmschematics
Maybe your wall plug is not respecting the norm.

So, what you call neutral should be the phase line.

Seen from you, the phase should be on the right, neutral on the left  
(plug in the wall).

It's easy to check, take a voltmeter (scale 500V AC), take one end  
(barefoot), and put the other one in the plug (each holes, one by one).
You have no risk ; if it is the phase line , the meter should move a little.
Don't forget that if you put the meter in Amperes, you will reach the  
cieling.

To comply to safety rules, manufacturers must protect the phase line,  
not the neutral (VDE, UL, IEC, ANSI, ISO...). So your wall plug  
connexions might be inverted.



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Re: Odd wiring in tube ampmschematics
On 12/6/18 12:04 PM, snipped-for-privacy@whidbey.com wrote:
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Almost all of those projects aren't done by engineers.
They're done by people parroting one another.

Back in the "good old days" of two wire non-polarized line cords,
the standard procedure was one side went to the fuse, if it had
one, the other side went to the switch. There was no engineering
behind that decision, it was strictly manufacturing, "We need one
less tie point."

Look at it as a series loop. It doesn't matter the sequence that
anything is connected in.

Three wire line cords:
Hot, to fuse holder (The point at the far end of the fuse) then to
the power switch. Not that you should rely on an open fuse to keep
your fingers off the hot side of a line inside a chassis.

--  
"I am a river to my people."
Jeff-1.0
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Re: Odd wiring in tube ampmschematics
I said with a voltmeter 500 VAC (some 1MOhms) in between you and the phase,
The measure should show about 5-10 VAC if you don't come from the shower  
but barefoot.

The neutral is easy to check ; around 5-10VAC betweent neutral and  
ground (a water pipe for instance or a heater in case of collective  
heating).


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Re: Odd wiring in tube ampmschematics
On Friday, December 7, 2018 at 8:47:44 AM UTC-5, Look165 wrote:
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If you are seeing an actual 5 - 10 VAC on the meter between neutral and ground in a household system, and the wiring is otherwise to-code (US NEC), something is wrong.  

Peter Wieck
Melrose Park, PA  

Re: Odd wiring in tube ampmschematics
On 12/7/18 11:15 AM, snipped-for-privacy@aol.com wrote:
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Probably under sized wiring, or a bad connection somewhere
along the neutral line.
A couple of volts is normal due to the normal voltage drop in
a conductor.


--  
"I am a river to my people."
Jeff-1.0
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Re: Odd wiring in tube ampmschematics
On Friday, December 7, 2018 at 12:49:02 PM UTC-5, Fox's Mercantile wrote:

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Maybe so. But that is enough to play havoc with such unimportant items as pacemakers, not to mention what it might do to audio and video equipment.  

Peter Wieck
Melrose Park, PA  

Re: Odd wiring in tube ampmschematics
On Friday, 7 December 2018 18:13:16 UTC, snipped-for-privacy@aol.com  wrote:
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how would a couple of volts mains drop have an effect on pacemakers?


NT

Re: Odd wiring in tube ampmschematics
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It won't. It also should not affect any audio or other equipment that is designed right. The only POSSIBLE problem might be turntable hum but even then...

Re: Odd wiring in tube ampmschematics
On Saturday, 8 December 2018 03:57:57 UTC, snipped-for-privacy@gmail.com  wrote:

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designed right. The only POSSIBLE problem might be turntable hum but even t
hen...

All domestic mains current loads are balanced, ie live & neutral carry the  
same & opposite current, resulting in nearly zero magnetic field. Pacemaker
s, like any life-critical medical equipment, are designed & tested to meet  
harsh real-world conditions & keep going.


NT

Re: Odd wiring in tube ampmschematics
snipped-for-privacy@gmail.com says...
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You should have seen the problem some jack leg caused where I worked.  A  
3 phase 480 volt 20 amp circuit.  The power came in one electrical box  
and going out of that to another box about 3 feet away.  For some reason  
the person doing the wiring ran 2 legs through one piece of connecting  
conduit and the other wire through another piece of conduit.  Sort of  
made it into a transformer with a shorted turn.  Really heated things  
up.


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