Hey guys, not sure if this is the right forum for this, but it does involve a tube amp!
I have an old reel-to-reel with some decent tube preamps. I have removed the preamps and plan to use them standalone. In the process, I am wanting to convert the old 2-prong plug to a 3-prong, grounded affair.
I understand that normally, as the unit is chassis grounded, I would simply connect the new ground wire to the main chassis ground lug where all of the units grounds are soldered. But in removing the power transformer case, I have noticed that that said lug has an additional wire that runs to a lug on the transformer marked "E", which then terminates at the 0V of the secondary 250v tap.
In this case, where is the best place to locate my ground wire to the wall? On the chassis lug as usual? If so, do I need to remove the earth wire running to the power transformer?
Thanks for your help, pictures of the power transformer included:
Imgur
I have an old reel-to-reel with some decent tube preamps. I have removed the preamps and plan to use them standalone. In the process, I am wanting to convert the old 2-prong plug to a 3-prong, grounded affair.
I understand that normally, as the unit is chassis grounded, I would simply connect the new ground wire to the main chassis ground lug where all of the units grounds are soldered. But in removing the power transformer case, I have noticed that that said lug has an additional wire that runs to a lug on the transformer marked "E", which then terminates at the 0V of the secondary 250v tap.
In this case, where is the best place to locate my ground wire to the wall? On the chassis lug as usual? If so, do I need to remove the earth wire running to the power transformer?
Thanks for your help, pictures of the power transformer included:
Imgur
not to the psu ground.....but to the nearest metal chassiss point....
if you are going to use an IEC power inlet, then to the screw fixing is a good place to put it...
no need to disturb existing circuitry...
if you are going to use an IEC power inlet, then to the screw fixing is a good place to put it...
no need to disturb existing circuitry...
Incoming mains ground should connect to its own tag on the chassis, somewhere near the mains inlet. As AJT says, this could be one of the screws holding the power inlet in place. The reason for having its own connection to the chassis is that you don't want any excuse to disconnect it during debugging.
>>>I am wanting to convert the old 2-prong plug to a 3-prong...
Why? From a sonic point of view I always have cut the earth, because it sound much better (open and clear).
If you are doing for security, just use an isolation transformer instead.
Why? From a sonic point of view I always have cut the earth, because it sound much better (open and clear).
If you are doing for security, just use an isolation transformer instead.
Safety. Cutting the earth connection is not the correct solution for "sonic" reasons.
Use a ground lift circuit such as two diodes in anti-parallel (rated to blow your fuse) in parallel with a 10R resistor between your system ground and chassis ground.
Use a ground lift circuit such as two diodes in anti-parallel (rated to blow your fuse) in parallel with a 10R resistor between your system ground and chassis ground.
Not just nonsense, but insanely dangerous nonsense. I hope that no-one follows this "advice."
ALWAYS ALWAYS ALWAYS have a chassis connected directly to mains earth. ALWAYS.
I can't agree with you more, so that begs the question when I am restoring old Heathkit equipment that never had a 3 prog plug should I change the circuit to add the chassis ground or leave it 2 prong. In the old days they must not have thought it was such a big deal, now we freak out about not having that 3rd prong.
Actually, no, sharing a screw with the IEC jack would fail a picky electrical inspection, at least for CSA here in Canada, as failure of the IEC jack could defeat the ground. Note that this is failure in the broadest sense of the word: someone removing the IEC jack is a failure mode. Also the IEC melting and releasing tension on the screw would be a failure mode. So I would recommend against sharing the screw.
And someone removing the jack would result in no ground regardless of where the wire is connected to the chassis. And no hot and no neutral either, eh?
😀 leadbelly may have a good idea....but.....i have done that in my amps, using the screw fixings....
planning for failure is fine, but i build my amps not to fail like that....
planning for failure is fine, but i build my amps not to fail like that....
Yes, strictly the screw used for a chassis safety ground connection must be used for that purpose alone and have star washers to prevent it coming loose. As DIYers we sometimes take short cuts, and so take small risks. The real problem is those DIYers who don't understand the issue and so take huge risks (for themselves and their families) by removing the ground connection altogether.leadbelly said:
talking from my own experience, i never had any failures of that nature in any of my amps.....now this tells something doesn't it....?
it all boils down really to what we have actually built and how the technical principles were applied in practice....the devil's in the details imho...
i would rather build things......rather than .....😉
it all boils down really to what we have actually built and how the technical principles were applied in practice....the devil's in the details imho...
i would rather build things......rather than .....😉
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