[R-390] R390 Posts HT Dropper, HT AC regulator

[Barry Hauser]

Hi John & List:

Hmmmm .... It appears the inflationary trend in mains voltage is being
perpetrated by a worldwide conspiracy.  Oh yeah, they'll say they had to
pump up the voltage to force the juice through the lines and reduce strain
on old power lines due to increasing current draw downstream - or something
like that.  Anyway, I have observed the same "up over" as you have down
under.  I'm located about 30 miles East of Manhattan/NY.

At times of low usage -- spring and fall with moderate temperatures and low
air conditioner up-time, the voltage can run as high as 127.  During very
hot days in the summer, I've monitored it as low as 95 V.  I don't know what
your "nominal voltage" is there.  In the US, in the last 50 years or so, it
is variously advertised at 110, 115, 120, rarely "125", and sometimes (as
spec'd on the '390 I believe) the odd figure of "117",  which, I suspect was
a hedge, but became popular for a time.

If the ideal voltage for the '390 is truly 117, 10 volts extra may be a bit
much -- as a regular diet.

One question is whether you are trying to adjust for sustained high or low
voltage vs. momentary fluctuations including surges and dips due to on-site
activity.

If it's the former, a Variac (autotransformer) can be a viable solution,
providing you monitor it full time with an accurate voltmeter.  For safety's
sake, if the receiver is on, but not attended to, you can crank it down a
bit below optimal, then tweak it when doing critical listening.  Some are
concerned that a slip of the wrist could sink your ship, uh , boatanchor..
The solution -- possibly chose one with a range switch -- for example, some
nominal 120 vac units have range switches labeled 0-120 and 0-140.  Of
course, the labeling is "nominal" and is subject to the same inflation
discrepancy, so the "120" may have been 120 when the supply voltage was 110
in days of yore.  Now, 120 may be more like 130, but it won't be 140 plus
10-15%.

If it is a cabinet enclosed unit and does not have the switch, very often
the autotransformer itself has the extra taps about 20 degrees off the end
taps and you can choose the appropriate one to add a switch.  Another
solution is to fashion a mechanical stop which can be defeated when
necessary.  The advantage to using an autotransformer is that you can also
use it to step up the voltage during a sustained power sag, AKA "brownout".
(Definite downside to a bucking transformer)  Another advantage or
disadvantage, depending on your persuasion, is that it provides yet another
knob and meter to enjoy.

Alternate possible solution, but a reach would be a high quality external
voltage regulator/filter as is typically used with computer equipment.
There are separate regulators and those combined in with battery backup.
There are a number of different combinations of those.  Some of the battery
backups are simple and just switch over from charging the battery to running
off it with the transverter.  Not much use for this application.  There are
others that add an integrated VR circuit, but still simplistic.  I believe
there are some that use the battery along with VR circuitry to regulat full
time, as if the battery were a glompus storage/filter capacitor.  However,
some and perhaps all of these are too noisy.  I have not tried them.  The
better ones have good filtering, but they are primarily designed for use
feeding computers with switching power supplies, so I don't know -- anyone
try any of these?  Another consideration is that some are more "twitchy"
than others and may introduce some transients of their own -- along with the
noise.

As long as you don't develop a habit of nervously twiddle the variac knob,
they're quiet.  Now before this sets off a rant that the R-390's are robust
and were designed to handled wide swings in line voltage, etc.,  I'm
referring to conditions of sustained high voltage in excess of 125, and
perhaps nearly equivalent to John's ~270 observations, which may put a
strain on things long term.  If your line voltage runs 115-122 or something,
I'd then say, well ... fuhgeddabowdit.  (30 miles East of NYC, remember? ;-)
and barely a stone's throw from one of the most infamous power companies on
the planet, including a nuke plant that was powered up just long enough to
be contaminated, but never went on line.   Yeah, it coulda' been woise.  If
there were a problem at that plant, it would have been almost impossible to
get off "Lone Guylund".  The evacuation plans were evaluated after they
built the thing, in the aftermath of Three Mile Island.  We should probably
build all our nuke plants down under and pipe the juice in.  The locals
don't seem to mind the our subs -- or maybe they do.  Are they stationed
there for strategic reasons -- or where they exiled?)  All that was OT, but
safely isolated in parentheses.  Which reminds me to remind you that
autotransformers are not isolated which is not a problem driving
transformered equipment, but bear in mind if you "borrow it" for some other
project.

Well, I wrote way too much again, so will now submerge for another six month
stealth tour.

Barry