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In Reply to: RE: tube choice posted by pictureguy on July 08, 2021 at 13:46:44
I'm not sure about the GFCI tripping. But possible.
The 5A fuse is not even in line with the switch directly. The switch is on the neutral, the fuse on the hot. Wired like the original Dynaco ST70 from days gone by.
Certainly doesn't meet UL.
Dan Santoni
Follow Ups:
I think the ground fault NEEDS ground. Any dsagreement in current between hot and neutral MUST be at ground......CLICK!
I'd need to see the direections for assembly. Some think AC is not what it IS......and might just wire the hot / neutral wherever and not care about fuse....it's in series, right? or the power switch, also in series.
I'd be very careful ......
Too much is never enough
Yes, you are right about the GFCI. Answered too late last night.
The fuse and the switch are in series. They need to be, but the fuse is on the live, and the switch is on the neutral, not directly in series with each other with the fuse first. Of course since the power cord is not polarized it can be flipped.
Dan Santoni
Even the CHEAP 16-2 cord I recently purchased was polarized.
ONE Wide blade and the other Narrow....And the cord is 'ribbed' on one of the 2 wires. So the orientation can be continued to the device being 'recorded'.......I had bought an EXTENSION cord and just clipped off the outlet knuckle (worthless, anyway) and used the cord......
So it'll only plug in ONE way, ragardless of 3rd wire ground. Or Not.
If / When I build this amp? I'll give thought to fuse / switch BOTH on the hot leg. NO REASON, IMO, for any voltage to appear between chassis and ground.
I think an error was made somewhere in the assembly. A blob of solder? A skinned bit of insulation? Lack of stand-off insulator somewhere?-
I can't believe that installing a 3-wire system (with ground as #3) and with voltage on that wire would NOT result in a tripped GFI. I'd personlly try the device in the bath or kitchen where the GFI outliet lives. If it trips (I give it 90%) than the device is UNSAFE and should not be used until the real problem is found.
But that's just ME.......
Too much is never enough
The AC never touches the chassis. At least in anything built after 1962. The AC circuit is entirely isolated from the chassis. So the argument of polarity and chassis grounding is wrong. FYI a power tranny does not require polarity. The AC wave being in one of two 180 degree phases make no difference in converting AC to DC.
Edits: 07/09/21
View YouTube Video
About 25 years ago, I asked one of our electrical technicians at work what the dots on the schematic of a power transformer meant, and he said "phase". Since none of my old tube equipment transformers were marked, I simply ignored it. Even the newer Hammond power transformer I bought has no polarity markings, at least not on their included schematic.
Your discussion with jedrider got me curious, and I found the above video this morning. Our Canadian friend in the video explained it in a way that not only could I understand (most of) transformer phase, but something more important. The video showed a simple way that I can test my unmarked transformers for phase, which I always thought would require a room full of expensive test gear.
Where I need to do some further research is regarding the benefit of proper phase. Is it simply higher or lower secondary voltage? Power supply efficiency?
My next thought was "Did the transformer winder wind in the same direction for all three secondary taps?" in a multiple tap PT, and does that matter, if I find proper phase for all three?
I haven't finished my coffee yet, and all this is making my head hurt. But I see I've got a lot more homework to do.
It's been my experience, at least with torroidals, that the capacitance to ground is different for each leg, as the circuits appear to pick up hum otherwise. Most torroidals are labeled such I believe and it should be followed.
AC is a 180 wave. Polarity is simply the point in the wave that is hitting the tranny. It's like a lightbulb.
So what you're saying is that if some inept electricians helper wired my socket wrong, which happens far more frequently that one would imagine, that your stereo is going to hum or not work?
Just because you can rewire a socket doesn't mean most other people can. So that would present a significant percentage of non working stereos.
"The AC circuit is entirely isolated from the chassis."
No, it's not. The schematic doesn't show the capacitance to the chassis from any of the primary components. Most power transformers that aren't hospital grade leak enough current to the chassis to kill a person who comes between the chassis and ground. It's unconscionable to build and sell a tube amp without a three-wire power cord.
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Buy Chinese. Bury freedom.
Keep up the honest discussion! SAFE
equipment MUST connect the service ground
to the chassis.
-Dennis-
> > "The AC circuit is entirely isolated from the chassis."> > No, it's not. The schematic doesn't show the capacitance to the
> > chassis from any of the primary components. Most power transformers that
> > aren't hospital grade leak enough current to the chassis to kill a person
> > who comes between the chassis and ground. It's unconscionable to build
> > and sell a tube amp without a three-wire power cord.False.
The power transformer has a few hundred pF at most from one end of the winding to ground, which can pass an AC current in the microamp range. Modern safety standards allow 0.7 mA (below the "startle" threshold of about 1 mA, which could cause someon to jump or drop something) and well below a hazardous current. GFIs trip at 4-6 mA, a level considered hazardous. A typical voltmeter is 10 megohms, a cheap one one megohm; can show a voltage even when a non-hazardous current is available.
However, a kitmaker does not build and sell an amplifer; and cannot get safety approval since he does not build it. It would require a 3-wire grounded cord to gain safety approvals (or to be double insulated, which is not practical for the power transformer or output transformers).
Edits: 07/10/21
Even if I was wrong (I'm not), what happens when the insulation deteriorates or there's an arc-over inside the power switch to the chassis? Only a third wire ground can protect the user from these and countless other hazardous conditions. Sure, you can trust your life to a Chinese interrupter. Not me.
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Buy Chinese. Bury freedom.
Your statement that transformer leakage could kill a person is false - it's minuscule. Yes, you can measure it with a voltmeter - but current is what's dangerous. This sort of design met safety standards for decades, though it would not today.
That said, I'm currently working on some amps from 1960 that have UL labels next to the (previous ) 2-wire cord. Now with grounded cords, like everything else I work on.
If you were interested in a retrofit?
Punching the IEC hole in the 16ga Stainless Steel chassis could be a problem. I don't thnk a regular 'nibbler' would work. Chassis punch is $$$ for a one time use.
MIght be easier to take a drawing to a machine shop and let THEM do it? This prior to any assembly.
Before any of that? make certain you have enough clearance behind connector......
Too much is never enough
I don't think a machine shop can punch that after the chassis is formed. Buy a Heyco strain relief to fit a 3-wire cord (16 or 18 gauge) and file the hole to fit. Incidentally, contrary to popular belief, many stainless alloys are no harder than mild steel.
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Buy Chinese. Bury freedom.
I would suspect a 300 series stainless.....Austentitic / non-magnetic......Available in the 16ga thickness and not expensive.
Still and all, 18% to 20% Chromium.......and a smattering of 'other'.....Including Nickel?
But I DO suspect it's pretty tough.....
I DO have a strain relief fit for CL2 wire.....I can't find the dimensions now, but it does work.
I used one on my KENWOOD Integrated when I re-corded it, up from 18ga to 16ga
i wonder what OTHER stainless alloy qualifies? I think 400 series is magnetic, mostly, while stuff like Invar and Monel are much more $$$......
Bob Latino himself answered my post about nibbling or punching the chassis....and he was not optimistic about the prospects...
Too much is never enough
"Bob Latino himself answered my post about nibbling or punching the chassis....and he was not optimistic about the prospects..."
And he's right. A small taper file (triangular) and small rat-tail file will take care of this. It's a half-hour job at most to carefully make it exactly right for the Heyco. Be sure to use calipers to measure the strain relief before filing the chassis. They aren't always the exact size specified in the data sheet. If you make the hole too large, there's no going back.
--------------------------
Buy Chinese. Bury freedom.
As you noted, not ALL stainless is 'created equal'....though by definition, must start at about 18% Chromium content. Without getting 'exotic', VTA probably commissioned a 300 series alloy. Some other VERY exotic alloys exist, like H1 which SPYDERCO uses to make knives for the marine enviroment which essentially WILL NOT CORRODE.......And they are $$$......
I'm looking at both the DRAWING and the PHOTO of the complete amp and I'm not certain of the clearance between an IEC connector and the transformer. I do NOT know how far 'below' the 'deck' the transformer protrudes nto the lower part of the amp.....The image doesn't have the 'depth' I'd like to confirm and no mechanical drawings are offered.
There IS space if the connecter were mounted on the TOP of the amp, 'prongs down'.......You would not need the 3rd wire unless you measured voltage from chassis to neutral.......You could check this easily using a GFI circuit in-house.
IF you could trace such voltage to the power transformer....IMO the only 'real' possibility, could a shielf of MuMetal fix the issue?
The Fix would take 2 minutes.....TOPS.......
Too much is never enough
IMO, the IEC hole is way too much trouble to cut. The Heyco is simpler and much faster, especially in stainless. Plus, you already have a "starter" hole at that location in the chassis. Even if you don't measure voltage to earth ground (highly unlikely), faults can occur at any time. There's no substitute for the three-wire cord in any piece of equipment installed within an audio system. Ix-Nay on the mu-metal.
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Buy Chinese. Bury freedom.
We were rewiring the utility and other switched outlets (all 110) on an ION IMPLANTER. The IDIOT that did the work managed a hot / neutral swap and the ENTIRE CHASSIS was HOT. Of course, he worked nites and was GONE for the next 2 weeks on vacation.
I've been around a LOT of high voltage. In E-Beam metals evaporation, the voltage is around `13kv.
I'm linking the manual. You'll see a FULL POWER Triode in the circuit. This was a WATER COOLED device and required a certain water purity since it was part of the circuit. A lot of current, too.
Ion implaneters have a 20kv Extraction PS which gets the ball rolling and the ions into the acceleration tube. Which is up to 200kv. The Glassman Power Supplies were mostly AIR as an insulator.
Wafer Fab, where I worked as a process and maintenance technician (2 differetn 'careers') was a dangerous place to work. All sorts of nasty chemistry.
So you don't have to convince TOO hard for me to go 3-wire to an amp.
I have MANY horror stories. How about a wrench dropped on the inputs of a trasnformer the size of a coffee table? Wrench simply vaporized with a VERY loud noise. Or the guy who was reaching Uder the base plate of an evaporator and got ZAPPED by the power supply? Or the METER we turned to charcoal whey measuring high voltage......I think it ARCED arounnd the HV probe shield and that was IT.
Lot smore funs stuff.
So In short? I REALLY appreciate your safety bias. Only thing? I have small bits for a DREMEL and may be able to get that hole right. I need to get a cord / relief 'set' so the cord workss with the relief.
Too much is never enough
Here's a 16-3 strain relief. 0.55 ROUND hole.
I could drill to 1/2" and GENTLY expand to correct size.......
I'd have to check out cordage, first, though.....
Too much is never enough
It's not round. The hole is either a D shape or an oval with two flat sides. That's what keeps the cord and relief from rotating in the hole. Check the data sheet for Heyco strain reliefs, you'll see what I mean. Also, there's a special tool to install these that prevents damaging the plastic. It compresses the relief into the cord while you push everything into the panel. I think you can find the tool on eBay, made by Philmore.
Coincidentally, I just ordered reliefs and 16-3 cords from Antique Electronic Supply. The part numbers are below, in case you want to look at the full descriptions. These are going into the amps I'm currently building.
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Buy Chinese. Bury freedom.
Other styles exist.......at least one for a round hole.
But I agree.. INSTALL is important and hole size critical. The one I just did on my ancient Kenwood is IN THERE for good....Well, I could get it out, but it is a real press-fit.
As the amp is issued? I'm not really in love with the simple Grommet used. That can be improved for minimal effort.
Too much is never enough
It's RECTIFICATION that converts AC to DC, but otherwise I get your point.
Many power tools are what was called 'triple insulated'.......and NOT 3-wire system required.
However? Somewhere in this thread is someone talkng about a voltage on the chassis of the amp.
This is a BAD situation. And IF True? .....my reasons are on the 'possible' list.
The 3rd wire.....GREEN.....connected to chassis is intended to drain misapplied voltage FROM the chassis TO ground. I think a GFI in that case would shut that circuit OFF....
Too much is never enough
There is no voltage on the chassis. There should never EVER be voltage on the chassis.
AIRTIME::
I was right......
PLEASE look at the posts from BLACKDOG where he notes 'chassis voltage'.......which I 100% agree should NEVER BE.
So, I fall back to what I said at that time about some kind of assembly ERROR .......
Too much is never enough
Of COURSE......
But I thought I read somewhere in this thread where someone SAID their was voltage on the chassis....
That is what got me started.....
Too much is never enough
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