mike wrote:
Andrew VK3BFA wrote:
tirade 1 deleted

Rubbish. Where do you get this 25w figure from,
tirade 2 deleted

Well, you could do the math...it's easy.

Shooting from the hip, firing off the one true, onesizefitsall, solution
when you don't know the particulars and are not accountable for the
result is...
well...it's the "internet way"!

mike

RANT
ON................................................ ..................................
I am NOT disputing your theory - its correct as far as it goes, youve
left out lots of other factors that, ideally, should be considered in
this case, But its irrelevant to the original question. And in real
life I would ignore it as being too anal retentive.

If the original poster needed to ask how to hook up two transformers,
then your quasi mathematical analysis would be totally innapropriate to
the job specifications. Did you think of this at all? It is covered in
most 1st year engineering course...(RTFM)

My method, with the light bulb, might be crude, (it is crude, so?) but
it will work. And have proved that it works, more times than I can
remember. Linear and switching power supplies.

A simple question - using the light bulb method, whats the WORSE that
can happen? If the amp is horribly faulty (and lets not even bother
about doing insulation tests on the (old) transformer, that would make
it even more complicated) then the light bulb will light to full
brilliance.

Even an engineer could see that theres something wrong, and then fault
find it. (After doing the math, of course)

The variac method - again, the same simple question - whats the WORSE
thing that could go wrong. And I will answer that, not from theory, but
from practice. The voltage is slowly ramped up until something fails
abruptly and catastrophically. With no current limiting beyond a mains
fuse in the variac (You did check its rating, didnt you?) the electros
will disintigrate like shotgun cartridges generating lots of additional
work. (no harm was done to the person, being a trained engineer they
had safety goggles on...didnt they?)

(The above assumes its a linear supply - if its SMPS, then the
switching devices sacrifice themselves in a vain attempot to save the
fuse)

I have spent my entire working life in this field - working as a
technician fixing up the design problems of engineers. Stuff that any
competent technician would know NOT to do, from practical experience.
In my working life, I have met approx 5 competent engineers. The rest
were theoretical bull**** artists who soon moved into management purely
on the strength of having a degree - they were as hopeless at that as
they were at engineering, but there they had less chance to do actual
damage.

Are you a "working" engineer - do you own a soldering iron? - lots of
theory, plenty of if/but/maybe/ because/planning, but no real
appreciation of what the problem is - firing up an old amplifier. Thats
all - its not a design exercise, theres no cahce of a Nobel Prize in
this one, the project doesnt need to be managed, no consultants needed
to give a "proffessional " opinon, no SPICE models needed - just how
to power up an amplifier with minimal damage.



RANT
OFF............................................... ................................................

woo........

TIRADE
ON................................................ ..............................................

And I am heartily sick of "armchair experts" making life bloody
complicated when someone asks a legitimate question that is best
answered without a theoretical textbook analysis - I have seen far too
many people at radio clubs made to feel inadequate because some
smartarse engineer has given a long winded incomprehensible, irrelevant
answer to a simple question. These people leave, and dont bother to
come to any more meetings, or ask any more questions.

One of the best teachers I ever had was an engineer - a very rare
person, a brilliant teacher and a competent engineer. He woked out
where the question was coming from, ie the level the student was
capable of understanding - he then started from basic principles, with
great patience, and took the student forward until they could
understand the rocket science behind the question.

And if you want to see a good textbook using this method, grab a copy
of 'The Art of Engineering" by Horowitz(sp) and Hill. read it - you
might learn something from it about communication skill.

If you cant help, dont hinder.


Andrew VK3BFA.

I