Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old December 6th 18, 07:04 PM posted to sci.electronics.repair
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Default Odd wiring in tube ampmschematics

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

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Old December 6th 18, 10:07 PM posted to sci.electronics.repair
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Default Odd wiring in tube ampmschematics

On Thursday, December 6, 2018 at 2:37:02 PM UTC-5, John Robertson wrote:

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.


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
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Old December 6th 18, 10:43 PM posted to sci.electronics.repair
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Default Odd wiring in tube ampmschematics

On Thursday, 6 December 2018 17:59:08 UTC, wrote:
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


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


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Old December 7th 18, 12:54 PM posted to sci.electronics.repair
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Default 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...).

a √©crit¬*:
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


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Old December 7th 18, 01:54 PM posted to sci.electronics.repair
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Posts: 92
Default 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.


Look165 a √©crit¬*:
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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