Hi,
No, I am not. I'm using one similar to one posted on this group before
(also described in the "Power and protection of modern tetrode" article).
It is based on a lm741 op amp (if I remember correctly) steering an N
channel mosfet shunt regulator. The reference is two 1% resistors and a
multi turn potentiometer (it only moves the voltage by about 5V).
The only disadvantage of it is that it requires +12V and - 12V to work.
I think it doesn't need a lot of overhead.
73,
Luk - SP4IT
On Sun, 1 Dec 2024, 22:10 Michael Tope, <W4EF@dellroy.com> wrote:
> Luk,
>
> Are you using the PA0FRI screen regulator circuit? If so, won't you need
> more than 360 Vdc input?
>
> 73, Mike W4EF.................
>
> On 11/30/2024 3:07 AM, flynth@gmail.com wrote:
> > I decided to replace the auto transformer arrangement with a custom wound
> > 230 - 2*130V transformer.
> >
> > Could someone please verify J chose the voltage correctly, please?
> >
> > I need 350V at 45mA max. The shunt regulator has constant current of
> > 35mA-45mA which results in up to about 16W of power turned to heat. I
> > choose 50VA transformer in the following way.
> >
> > 350V+10V for losses or sags /1.41=255V AC
> >
> > I can order these transformers with a step of 10V up to 230V so 2x130V
> > seems a correct choice.
> >
> > 73,
> > Luk - SP4IT
> >
> > On Sat, 30 Nov 2024, 11:49 ,<flynth@gmail.com> wrote:
> >
> >> Now that you say it that way I start suspecting the auto transformer.
> >> Assuming nothing is miswired (and I have to rewire anyway to route the
> >> wires nicely - currently it's only a "working" setup) it is the only
> place
> >> that is not fully isolated.
> >>
> >> As expected in an auto transformer the neutral just passes through to
> the
> >> rectifier then minus of the rectifier is connected to the ground/case.
> >>
> >> I had RCD trigger before I fitted the auto transformer, but only once,
> so
> >> it may have been a temporary short.
> >>
> >> This is not ideal. I have to use it as auto transformer as all normal
> >> transformers I have, have far too high voltages. (for example a 230 to
> >> 415,after rectifying it results in 580V. That turns into a pot of heat
> if
> >> it has to be shunt stabilised to 350V. It's very hard to find 230-300V
> >> transformer.
> >>
> >> The "auto transformer" is a normal 240-2*36V toroid but connected like
> >> this:
> >>
> >> Low side of 240V is neutral that passes through, high side is connected
> to
> >> live 240V, then low side of the first 36V is connected to that, high
> side
> >> is connected with low side of the other 36V. Finally the remaining high
> >> side has approximately 300V AC and goes to the rectifier. I think it is
> the
> >> most likely culprit.
> >>
> >> 73,
> >> Luk - SP4IT
> >>
> >>
> >> On Fri, 29 Nov 2024, 20:20 Michael Tope,<W4EF@dellroy.com> wrote:
> >>
> >>> Luk,
> >>>
> >>> At least for amplifiers I've seen here in North America, the isolation
> >>> between the chassis metal and the power mains neutral typically come
> >>> from the HV transformer (and any additional transformers that are used
> >>> for producing things like filament voltage, control voltages, etc). Do
> >>> you have any connections between the lines on the primary side of your
> >>> transformers and the grounding conductor? In other words, I am trying
> to
> >>> understand why you need an isolation transformer to prevent RCD/GFCI
> >>> trip when the transformers in the amplifier should provide that
> function?
> >>>
> >>> 73, Mike W4EF
> >>>
> >>> On 11/28/2024 3:52 PM, Lukasz wrote:
> >>>> 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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