I'm going to be doing some work on a few vintage items, thought I'd address this as long as I'm opening up the chassis.
They all have 2 prong (live and neutral) power hardwired, no ground. I was thinking about fitting a standard iec inlet and attaching the ground to chassis, as is common practice. Or maybe just hardwire a 3 wire power cable, no iec inlet.
Why would the designers have used 2 prong instead of 3?
They all have 2 prong (live and neutral) power hardwired, no ground. I was thinking about fitting a standard iec inlet and attaching the ground to chassis, as is common practice. Or maybe just hardwire a 3 wire power cable, no iec inlet.
Why would the designers have used 2 prong instead of 3?
Even in 1960 (yes, in South Jersey, near Rt73 and Rt130), most new houses were mostly 2-pin. Old houses were 2-pin through, uh, today? The 1947 house I sold in 2020, I'd only partly re-wired to a 3-pin system. The 1830 house I sold in 2009 will never be 3-pin except in two rooms that I slaved-in for a week. (Idiot prior owners cut-off the annoying extra wire.)
Yeah, rewired much of my 1950 home to 3p and even installed GF ones near water in '77, but didn't have to and still don't AFAIK since 2p was the code when built. IIRC the code changed circa mid '60s, though googling 'says' '69, so may have been a Cutler-Hammer and/or all affected electrical power/controls manufacturer's mandate in anticipation.
Stage-amps and power-tools rushed to 3-pin in the 1970s. I do recall that Hi-Fi did not. Less exposure to water? Stray grounds?
FWIW (not much) the only shock I ever got from indoor hi-fi was from a case-screw into a transformer winding. I could not find the problem case off; case on OWCH!
FWIW (not much) the only shock I ever got from indoor hi-fi was from a case-screw into a transformer winding. I could not find the problem case off; case on OWCH!
It may be a good idea to keep up to todays standard?! I see countless cases of light electroshocks because of connecting 3 pin devices to 2 pin wall sockets here and can only say it is better to have PE than to do without. Mains filters also work better.
What old devices here have is that chassis is often connected to Audio GND so connecting chassis to PE now makes a direct connection of Audio GND to PE. When this is done in a few devices things are safe indeed but a ground loop is a fact. It depends on brand and the year of manufacture but separating Audio GND from PE is easy in one device and difficult in the other. Ideally only chassis/casing should be connected directly to PE.
What old devices here have is that chassis is often connected to Audio GND so connecting chassis to PE now makes a direct connection of Audio GND to PE. When this is done in a few devices things are safe indeed but a ground loop is a fact. It depends on brand and the year of manufacture but separating Audio GND from PE is easy in one device and difficult in the other. Ideally only chassis/casing should be connected directly to PE.
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Over this side of the pond in the UK we've had 3 pin for ages...
Most hi-fi & TV stuff is still only "2pin" as its classed as "double insulated".
Double insulated means that the item doesn't require it, i.e. not part of the circuit, also that if anything fails/explodes the outer case that a person touches will not go live, & that the grilles/openings in the outer case are small enough so that you cannot easily poke stuff into the inside & touch a live part.
Thing is over here most incoming mains to the main supply switch (before electrical meter) is only a single core, with the neutral being the steel wire armouring....& the neutral also doubles up as the "Earth"...P.M.E...(protective multiple earthing)....
My metal cased double insulated 2 pin only hifi was giving me static shocks as its isolated from the planet (floating so potential difference) due to the plastic feet on the cases.......let alone the big rubber Sorbothane pucks!.. The amp/voltage difference/leakage was within the spec for double insulated. I wired the 3rd pin (earth) of a plug to the metal cases of my hi-fi...first to the amp & the the other items back to the amp point.. This additional plug is plugged into the same mains filtering double wall socket as the hifi is....so no "loop".
Most hi-fi & TV stuff is still only "2pin" as its classed as "double insulated".
Double insulated means that the item doesn't require it, i.e. not part of the circuit, also that if anything fails/explodes the outer case that a person touches will not go live, & that the grilles/openings in the outer case are small enough so that you cannot easily poke stuff into the inside & touch a live part.
Thing is over here most incoming mains to the main supply switch (before electrical meter) is only a single core, with the neutral being the steel wire armouring....& the neutral also doubles up as the "Earth"...P.M.E...(protective multiple earthing)....
My metal cased double insulated 2 pin only hifi was giving me static shocks as its isolated from the planet (floating so potential difference) due to the plastic feet on the cases.......let alone the big rubber Sorbothane pucks!.. The amp/voltage difference/leakage was within the spec for double insulated. I wired the 3rd pin (earth) of a plug to the metal cases of my hi-fi...first to the amp & the the other items back to the amp point.. This additional plug is plugged into the same mains filtering double wall socket as the hifi is....so no "loop".
All very interesting thanks!
I just opened one of the amps up, and it is ridiculously densely packed. I'd have to take out the main board and half the components just to see if there's any room for the iec. I'm betting there's no room, so I'll leave it alone.
Look at the size of the transformer! No wonder why it weighs a ton.
On the bad side, the power cord is cracked in a few places. If I flex it I can see copper. I've never used liquid electrical tape, but I'll try it. If I decide to sell it, I'll definitely have to note that in the description. Ugh.
I just opened one of the amps up, and it is ridiculously densely packed. I'd have to take out the main board and half the components just to see if there's any room for the iec. I'm betting there's no room, so I'll leave it alone.
Look at the size of the transformer! No wonder why it weighs a ton.
On the bad side, the power cord is cracked in a few places. If I flex it I can see copper. I've never used liquid electrical tape, but I'll try it. If I decide to sell it, I'll definitely have to note that in the description. Ugh.
Attachments
Except that we have 2 cores, all this is very common in the US. From street to meter to fusebox is 2 hots inside steel armor-wrap neutral/ground.
(My house has un-armored feed; most of the 500 feet is two Aluminum hots spiraled around a Al-clad steel messenger/neutral/ground to the top of the meter pole. Past the meter is three black wires, I dunno how they got that right.)
All copper here and color coded 3 phase 400V 50 Hz power to the home and it is up to the customers to decide to have single phase 230V or high power 3 phase sockets. Great system.
First post... "vintage items" so no double insulated.
So 2 lives/lines??....Not surprised if they used a couple of cheap aluminium cored cables.... Aluminium was used over here for main cables buried in the ground when copper prices went through the roof decades ago...& then as time went by they realised that Aluminium isn't as good for long term "bury & forget"...
To the best of my knowledge "double insulated" has been around since at least the early 1970's...when the OP said his amps are from...
EDIT:- infact it was invented in 1968
https://patents.google.com/patent/US3476960
Thank you for reminding me that UK electricity is the best in the world!
Did you read the (US) patent?
"...the power tool or appliance is more commonly referred to as being double insulated."
I read that as saying "double insulated" was prior art, and common, when US3476960A was written. US3476960A is "an improved double insulated power tool...".
Selectively quoting me?....
I also stated:-"Aluminium was used over here for main cables buried in the ground when copper prices went through the roof decades ago...& then as time went by they realised that Aluminium isn't as good for long term "bury & forget"..."
Thus proving that even over here they used Alu cored stuff for a short time..
& yes I did read the patent....thats the earliest definitive usage of the term double insulated that I could find in a technical document....there may be earlier stuff that I haven't found.
The only reason that I posted that link was because the OP stated his amps are from the 1970's, & I had mentioned double insulated & another poster had queried my statement implying that double insulated wasn't around in the 1970's...when it was!
In the US type system the third conductor is there for safety.
In an old 2 wire building, you can install a GFCI receptacle which will allow you to use 3 pin plugs.
In an old 2 wire building, you can install a GFCI receptacle which will allow you to use 3 pin plugs.
There is no room... If the channels have high offset voltages, I'd take a look at the beta's on the input pair. From experience, degraded beta on the apt-1 input pair will result in high output offsets. Mine went so far out it triggered the protection. The thing is tight inside. I did some re-capping while I was in there and getting the boards out is a nightmare. Another suggestion, take photos, re-packing will be easier.