Phil Allison wrote:
"Patrick Turner"
When I measure the "240Vac" here is usually is stable enough to get a
nearly constant reading on a DMM,
** Must be a basic 3.5 digit one ( 2000 count) with only 1 volt
resolution
when reading 240 volts AC.
Any DMM with a larger count allows changes of 0.1 volts to be seen -
then the last digit is never steady.
Indeed, I'll get 240.XX Vac maybe even 24X.XX if the voltage is just
either side of 240.0Vac.
That's less than 1% Vac change.
** Another completely irrelevant reply.
Yawnnnnnnnnnnnnnn ...
But at least you are awake.
But it slowly varies between 235Vac on cold winter nights of heavy
loadings to 255Vac when load is light.
** What drivel.
Not so, this is without changing local loads here in my shed.
** Another irrelevant reply.
Rarely does the mains ever bounce rapidly between 235Vac and 255Vac.
** More irrelevance - since I never claimed it did.
Didn't you cite the effect of turning a heater here?
Don't let the details bother you.
It will instantly drop by 7 or 8 volts if you switch a ( 2.4 kW) electric
heater on AND jumps up by 6 volts when the ( 2kW) jug turns itself
off
when it has boiled.
Not necessarily so.
** Now that IS a blatant lie.
Not necessarily so. But cable length and its inductance and the COLD
resistance of the heater all work to make *some* change in mains voltage
amplitude. Depends on variables.
To best avoid the effects of the variables, regulation should be
employed, OK?
I for one live in a world where most gear I use can cope with mains
being between 235Vrms and 255Vrms because of its in-built regulation in
the case of PC PSU, CD player, TV set, all my oscilliscopes, and other
test gear, etc, and in a phono amp originally built in 1993. No reg in
power amps.
I dont have a B+ regulator in the same phono amp now which has excellent
LF stabiity in the output signal, see the PSU schematic 3/4 dowm the
page at
http://www.turneraudio.com.au/preamp...ated-2006.html
There is a reg for the heater supply though, mainly because its so easy
and reliable to do at low V, and have low hum from heaters anywhere.
The B+ Vdc rails are *allowed to wander* up and own where they want.
Triode preamps can sustain wide variations of Vdc applied, and one with
a nominal B+ = 280Vdc will work with 350Vdc or 200Vdc.
While playing a record, I can turn off the phono amp and then back on
again and hear nothing.
Anyone can try it and see what happens to the AC voltage on the same
circuit.
When I look at the rectified Vdc, it shows the expected variations of
+/- 30mV.
** Complete ********.
No.
** Another BLATANT lie.
Any unregulated DC supply FOLLOWS all variations in the AC voltage by
the
same percentage.
Agreed.
** Then stop posting ****ING STUPID **** that says otherwise.
You misunderstand me.
** NO - you completely misunderstand the point.
Er, what exact point are you making?
My point is that Vdc changes at the resevoir cap in a PS will change the
same % as the changes in Vac of the mains. But the rate of the change
will be different for Vdc at the end of a few sections of RC filtering
after the Cres because of the time constant involved.
Suddenly turning on a cold heater element won't cause a huge sudden Vdc
blip if the filtering has a long time constant. If the Vdc sags 1% or
10% because of a heater being turned on, then the rate of Vdc drop is
slow, and the idle Vdc electrode voltages at tubes and bias voltages
across coupling caps then all change but they can adjust slowly, and
there are no audible artifacts produced as a result because of the
enormous dynamic range of the tubes. Very slow signals are attenuated by
the RC couplings. And the point I make about my house is that a heater
used here does not cause a huge Vac change, and thus does not cause a
large Vdc change. My preamp without a B+ reg will work fine where mains
voltages are less well regulated than here.
In other houses with longer leads, perhaps much worse mains regulation
exists, ie, the output resistance of the wall plate outlets is much
higher than I have.
In 14 years of commercial operation I have never had any person tell me
that he has an audible fault which I found was as a direct result of LF
mains jitter and variations. I've repaired plenty of failed regs though,
and to make sure rates of B+ level change is harmlessly slow, I have
often removed ****y little 16uF caps and installed 470uF modern types.
Patrick Turner.
.... Phil