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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