If you are talking about the circuits described in the article by G3SEK
(QEX October 1997), then you better take another look. In the article he
advises that the input voltage should be at least 40V higher than the
desired regulator set point. This make sense. A shunt regulator needs a
series ballast to work against.
There is a copy of the G3SEK article here:
https://www.tmchistory.org/tmc_restoration/PAL-500/power and protection
for modern tetrodes.pdf
73, Mike W4EF........................................................
On 12/2/2024 7:23 AM, Lukasz wrote:
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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