Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on February 26, 2025, 05:49:52 pm
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Thought i might try and contribute a simple pic and understanding of why the Neutral wire must be connected properly in your amplifiers.Their is so much miss information online these days even the simplest task can become a guessing game. Can't guess when working with any voltages that could hurt or even kill you. God Bless All!
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Nice graphic! I find that it also helps to check the ends of the wires and the prongs of the plug with a multimeter just to confirm, especially if you've scavenged the wire from some other electrical item. You never know if some factory threw quality control out the window and wired things wrong.
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Nice graphic! I find that it also helps to check the ends of the wires and the prongs of the plug with a multimeter just to confirm, especially if you've scavenged the wire from some other electrical item. You never know if some factory threw quality control out the window and wired things wrong.
Yep you're right and color codes don't follow the standard they used to all the time.
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Thought i might try and contribute a simple pic and understanding of why the Neutral wire must be connected properly in your amplifiers.Their is so much miss information online these days even the simplest task can become a guessing game. Can't guess when working with any voltages that could hurt or even kill you. God Bless All!
Note that many regions require dual pole mains switches.
. The best way to attach the ground (green) wire to the chassis is to ... use a double nut on a ring terminal to affix it to one of the power transformer's mounting bolts.
No.
1/ the wire must be mechanically secured to the ring terminal lug, eg crimped. It can then be soldered but soldering only is no good, eg fault current passing through the joint can heat the solder to melting point, and any tension on the wire could cause it to become detached.
2/ There's no mention of wire length?
Inside the chassis, after the cable grip, the earth wire must have sufficient spare length such that if the cable grip failed and the cable was pulled out, the earth wire would be the last wire to get pulled off its lug.
I don't know whether soldering the wire directly to the chassis is acceptable. I don't recall seeing it used in any modern equipment.
3/ For some reason, a mains transformer fastener seems to be the default choice to use to clamp the earth safety lug to the chassis. That’s about the worst option for the chassis safety earth fastener.
Firstly, mains transformer fasteners are already the most mechanically stressed of any on the amp chassis. So straight off, it doesn’t seem a good idea to also entrust it with the amp’s only safety critical connection.
Secondly, if the mains transformer fasteners pass through the transformer’s lamination stack, they will additionally be subject to magnestriction.
Thirdly, a lamination stack doesn't resist long term compressive force over time in ghe same way that a solud block of metal does, rather it will tend to compress together, eg under compressive force of the bolts.
The net result being that no matter how much torque is used to tighten them up / locking arrangements used, mains transformer fasteners tend to get loose over time. Hence potentially leaving the safety earth not properly connected to the chassis.
My understanding is that modern standards require a dedicated fastener be used to give the best chance of ensuring that the safety earth lug stays connected to the chassis metalwork. ie drill a new hole.
Use a threaded screw and a nylok locking nut or similar, preferably high tensile, with a toothed star washer between the lug and chassis metalwork.
I've copied most of the above text from a post I made over at TGP https://www.thegearpage.net/board/index.php?threads/2-prong-replacement-two-ways-or-not.2494779/#post-37571766
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No fear of showing my age: fastening mains ground to a tranny bolt was standard (as of 20 years ago). Though 2 chord wiring was once standard also. AFAIK new standard is solder to the chassis. This strikes me as a bad choice: it requires a powerful soldering gun; a bad solder joint is dangerous; and the high heat is bad for existing components if retrofitting into a populated chassis. Second modern choice: dedicated bolt. But what if it's a vintage amp? I still prefer the tranny bolt, using a lock washer & double nuts.
What do you think?