Hi Lukasz,
I use a tube amplifier which I have built in 1975 in a no RCD environment.
It uses a 3-phase HV power supply as well as single phase small power
supplies.
The amplifier is of course grounded with its chassis to safety ground
(PEN).
The amp chassis is also RF ground.
B- is routed separate from the power supply to the amp but clamped to
chassis ground via a 10 ohm resistor and a diode, that is a requirement for
metering grid and anode current. Without metering it could be connected
directly to the chassis.
Power supply chassis and amp chassis are interconnected.
HV transformer is YY wired, rectifier is B6 full wave, so no neutral
connected.
Amp works with RCD now after I moved qth.
You might have a problem with your power supply when the RCD trips.
How is your grid wired, with what system?
<https://www.bender.de/fachwissen/technologie/it-system/netzformen-zur-stromversorgung-ein-vergleich/>
73
Peter
-----Original-Nachricht-----
Betreff: Re: [Amps] Preventing current flow on PEN/EGC (protective earth
conductor/equipment grounding conductor).
Datum: 2024-11-29T00:53:31+0100
Von: "Lukasz" <sp4it.mail@gmail.com>
An: "jim@audiosystemsgroup.com" <jim@audiosystemsgroup.com>
Hi Jim,
It is similar here in the EU as far as I know.
A typical way devices, are constructed here is that the ground (including
the case if made of metal) is not used as a normal current path in the
device. One sees current flow on that ground only in a fault scenario.
This means RCD/GFCI protections can work as when it see any discrepancy in
the live/neutral current balance it shuts the circuit down.
These rules normally mean one always has a return current path within the
device that is separate from ground (neutral, DC minus etc), but this is
difficult when the amplifier is entirely made of metal and one would prefer
to have a current return plane (for example the floor if the case) rather
than route separate connections for DC minus and RF ground.
This is not how OLD devices were made. I have a couple of old lathes and
mills that do use the steel frame as neutral/ground(one connector called
PEN) . This is how, it seems, all tube amps are built I saw pictures so
far.
So my question is, if one wants to build a tube amp in a modern way.
Properly grounded, is building a case within a case and electrically
isolating the two the only way? Or has anyone managed to build a tube
amplifier in a single grounded steel case. That works normally within the
usual electrical systems (with gfci/rcd protected circuits). If so, please
describe how are all the current return paths done.
73,
Luk, SP4IT
On Wed, 27 Nov 2024, 23:05 Jim Brown, <jim@audiosystemsgroup.com> wrote:
> Hi Lukasz,
>
> In North America, the protective earth MUST be carried in the same cable
> with the current-carrying conductors, and MUST be bonded to the chassis
> at the point where that cable enters. I'd be surprised if it's different
> in EU -- it must be done that way to be protective!
>
> There's another requirement in NA -- all grounds (earths) MUST be bonded
> together. Again, protective against both lightning and electrical shock.
> So when power goes through ANY transformer that's not part of equipment,
> protective earth MUST be carried from one side of the transformer to the
> other.
>
> I don't remember about EU, but I do remember that in the UK, no earth
> connection to the power system is permitted -- that happens only within
> the power distribution system.
>
> When thinking about this and antennas, remember that the earth is a big
> resistor, and parts of antennas like radial systems are NOT intended to
> couple to the earth, but rather to shield the EM field from the earth,
> and to provide a low resistance path for the antenna's return current.
> The only antennas that benefit from an earth connection are SOME
> receiving antennas, like Beverages and loops.
>
> 73, Jim K9YC
>
> On 11/26/2024 8:10 AM, Lukasz wrote:
> > Hi,
> >
> > Is there some way to build a tube amp in a metal case, using the case
as
> RF
> > ground, and not have current flow out of the amp through the grounding
> > conductor? (other than isolating that ground from the case entirely,
> which
> > presents it's own problems - for example capacitive coupling to the
> case).
> >
> > I'm currently experimenting with an amp and I have to power it via an
> > isolation transformer (the high voltage is 3 phase on its own circuit
> with
> > no GFCI temporarily) or my RCD will trigger.
> >
> > The high voltage power supply is an old military device that used its
> > chassis as ultimate DC ground (hv ground connects to it through a
> > overcurrent protection coil).
> >
> > Then I also used the chassis as ground for DC HV, screen and grid
> supplies.
> > This I could swap, but it's the RF ground (especially the Pi tank) I'm
> > concerned about.
> >
> > Is essentially isolating amp RF ground from the grounding conductor
> > (PEN/EGC or whatever it's called where you are) the only way?
> >
> > 73,
> > Łukasz, SP4IT
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
>
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