Silvertone 1448

[Leo_Gnardo]

Ok I get it guys. Haha I had a feeling I'd get the ruler on the wrist for even trying this. Thank you for the concern and insisting.

Ruler on the wrist beats getting a major, potentially killing shock. Or setting gear &/or wires afire. Randall in Ft. Myers went thru this a couple weeks ago with a clock radio, and an even cheaper iso transformer. Same one ought to be able to run that mini amp. You still have to box it, add a fuse & wires. Looky here:

N-68X Triad Magnetics | Mouser

[nickb]

Ok I get it guys. Haha I had a feeling I'd get the ruler on the wrist for even trying this. Thank you for the concern and insisting. So, in my drawing, I see no direct connection of the HT to safety earth. Are you saying that the main filter caps should NOT be grounded to earth? Is this why the breaker is blowing? I think I'm missing a basic electronic rule here. Which is embarrassing honestly, been working on amps for about 16 years. There's something I'm missing about this amp having the GROUND be the neutral of the mains, and not earth ground. And I'm guessing this is because there is no ISOLATION transformer. Final question here: This customer may or may not want to pay for the iso and labor. If so, should I convince him because of the "widow maker" issue? And if so, how could they manufacture amps like this back in the day with the risk of killing people??

Your safety earth is connected to the chassis, right? Trace the HT current: From live, through the rectifier, through the tubes to the chassis and so to safety earth and finally back to neutral at the local connection point.

[lowell]

Thanks all. Nickb, thanks for bearing with me on this. I'm confused by this statement "Back to neutral at the local connection point." What's the local connection point.

[nickb]

Thanks all. Nickb, thanks for bearing with me on this. I'm confused by this statement "Back to neutral at the local connection point." What's the local connection point.

Well, I was trying to be general. In the US the neutral is connected to earth at the electrical service entrance, often that's in the breaker box, I think.

[lowell]

Ok. I had no idea that was connected. Directly connected? Are earth and neutral the same??

[nickb]

Ok. I had no idea that was connected. Directly connected? Are earth and neutral the same??

Well, yes and no. It's a surprisingly big and complex subject. Well beyond the scope of this thread. Searching for things like "Electrical Power Distribution" and "Neutral/ Earth Bonding" kind of things should get your on the right path.

[The Dude]

YOU DO NOT UNDERSTAND:
FIRST YOU ADD THE ISO TRANSFORMER
SECOND: you find your problem magically DISAPPEARED

YES. I find it best to always fix the obvious problems first.

[Randall]

Randall in Ft. Myers went thru this a couple weeks ago with a clock radio, and an even cheaper iso transformer. | Mouser[/url]

And I'm going thru it again with a Danelectro Cadet 122. It's almost the same as the Silvertone here in question except mine does not have a filament transformer, all 3 are wired in series. I have the Triad N-68X on order, but I have to admit to also being unsure of how to wire the grounds and safety ground. Right now I have all the HT side grounds on a terminal strip where the neutral from the iso secondary will go, NOT connected to chassis. It seems to me that point goes to chassis thru the 68K resistor on the preamp side where those grounds ARE at chassis, via a foil sheilding strip the jacks and pots are mounted on that also runs under the chassis. Is this correct?

[Leo_Gnardo]

Ok. I had no idea that was connected. Directly connected? Are earth and neutral the same??

My understanding of US NEC (National Electrical Code) has Ground and Neutral "bonded" at the service box. IOW, tightly connected within the breaker box, and nowhere else.

What I've done with "widowmakers" is have neutral go to the negative end of the audio & power supply circuits. Ground continues from the AC plug, around the iso transformer, and connected to the metal box that contains the amp. It may be a bit tedious putting insulator washers on each input jack, providing separate circuit grounds instead of using the chassis as "common", etc. but it's what you have to do.

[Randall]

Quote Originally Posted by Leo_Gnardo

"Randall in Ft. Myers went thru this a couple weeks ago with a clock radio, and an even cheaper iso transformer."

And I'm going thru it again with a Danelectro Cadet 122. It's almost the same as the Silvertone here in question except mine does not have a filament transformer, all 3 are wired in series. I have the Triad N-68X on order, but I have to admit to also being unsure of how to wire the grounds and safety ground. Right now I have all the HT side grounds on a terminal strip where the neutral from the iso secondary will go, NOT connected to chassis. It seems to me that point goes to chassis thru the 68K resistor on the preamp side where those grounds ARE at chassis, via a foil sheilding strip the jacks and pots are mounted on that also runs under the chassis. Is this correct?

[J M Fahey]

Something which a few do not seem to have fully clear (agreed that it's somewhat confusing) is that:

1) neutral and ground are NOT the same, and not to be connected, at least as house wiring goes, although the utility company does join them ... eventually .... somewhere ... but you must ignore that and treat them as separate ... which they are at home and that's all you should care about.

2) they are joined by the utility company anywhere from the "connection box at your home door" (don't know how it's called in USA/UK/Oz/NZ although probably by 3 or 4 different names ) to the pole/pit where the area transformer is located.

3) the point is that they are used for different purposes:
a) *normally* Neutral carries all current consumption return from anything plugged in that house and Ground carries "almost nothing" , the microscopic (less than a few mA) leakage current which any real world device has.
It also grounds hum/noise/buzz in our audio equipment, again a very small current.
b) in a dangerous/deadly situation as in when insulation breaks down bad or simply there is wiring/operator error, and hot touches metallic chassis, now Ground must carry as much current is needed to blow mains fuses , might be 100 Amperes peak.
Given its important lifesaving job, it needs to be a separate conductor, a separate plug leg, period.

4) now we have potential (literally ) problem: since important current passes through neutral (the full home consumption) and none or microscopic through ground, and all conductors have resistance, it is normal to have a few V difference between Neutral and Ground.
I have measured up to 25VAC difference on 220V lines.

IF you join neutral and ground at your outlet (or in the widow maker) an important current will pass through ground.

Just speculating, but suspect not far from the truth: I bet modern RCD devices measure either/or/both current through ground or voltage difference and trigger the cutoff relay when they find something they do not like.

Might explain Lowell's RCD triggering with joined Neutral and Earth, even if he's not actually being

[Justin Thomas]

RCD = what, exactly? Thanks! As in, the actual acronym...
And while I'm at it, is it GCFI, or GFCI? I know what the letters stand for in that one...

Justin

[The Dude]

https://en.wikipedia.org/wiki/Residual-current_device

[Justin Thomas]

So, it's like the sockets I see in bathrooms with the little buttons for "Test" & "Reset," and both of the buttons are always covered in rust, and I wouldn't want to touch the buttons for fear of crumbling plastic, shorted terminals, and blown-off fingers...

Something about moving parts in a socket in a steamy constantly damp bathroom... Maybe it's a good selling point for those $25k 24-karat-gold-plated sockets... "Not only will your electric razor SOUND smoother & less buzzy, but this outlet could SAVE YOUR LIFE!"

Justin

[Enzo]

Juan, in most US codes, the ground wire from the outlets around the house is bonded to the neutral in the service panel - the big breaker box on the wall in the basement. There will be a ground stake outside int he dirt also wired to the ground in the panel.

Leo, code/schmode. It SAYS it will be wired thus and so, but in reality, there is a reason we carry those outlet testers around - it is not that rare that an outlet is wired wrong. You cannot then guarantee the things will be safe by wiring them internally as if all outlets are wired correct.

Grounding is simple. The point of the isolation transformer is that it, well, isolates the mains from the 120v inside the unit. The reason you cannot ground with a three wire cord a stock hot chassis amp is that you;d be grounding one side of the mains. With an iso, the chassis and wiring HAVE NO connection to the mains, so you are free to wire a third prong ground direct to the chassis. Yes, it goes around the iso. The ground itself was never the issue, the issue was the mains wiring being coupled to the chassis.

And having done that, really, I;d just leave the old semi-isolated grounding in the circuit as it was.