"Phil Allison" wrote in message
...
Arfa Daily wrote:


The VA rating and regulation percentage of commercial mains
transformers
closely follows their primary resistance, not by any simple formula but
ones with the same resistance have similar VA ratings.

Egs, for 240V rated transformers:

50VA = 60 ohms & 13%
160VA = 12 ohm & 8%
300VA = 4.7 ohms & 4%
800VA = 1.4 ohms & 4%
1000VA = 1.1 ohms & 4%



That's an interesting observation, Phil. I will keep that noted, as it's
potentially a good 'reverse lookup' for determining if a tranny has
shorted
turns on its primary, if you know its VA rating


** That is a big "if" - cos with transformers fitted to commercial
products it is not published.

I keep an index book with primary ohm values for commonly seen gear, also
the mains rms current draw at idle, with standby off and on - if it
exists.

Egs:

Marshall JTM60; 6.5ohms (250VA) 0.16A, 0.44A

Marshall VS100; 10.2ohms (175VA) .17A

Phase Linear 400; 1.9ohms (600VA) .17A

Roland Cube 60; 12ohms (160VA) .1A



.... Phil


I used to do all sorts of stuff like that to make life easier for the
future, but somehow, I just don't seem to have the motivation any more. I
guess it's just part and parcel of getting older. I seem to really lack
enthusiasm the last couple of years. Every now and then I get one that
provides some satisfaction. Like the Studio Due Shark 250 moving head last
week. It was really slow to do its power on reset. It found the pan endstop
microswitch ok, then reversed direction as it should, to index the opposite
end of the pan range. But it moved REALLY slowly doing this. And instead of
stopping just short of the mechanical end point, it ran into it, leaving the
pan stepper motor clunk-clunk-clunking. And there the reset process stopped
for ever. I opened it up and took a look at the output from the pan position
encoder. It's made up of a slotted wheel running in two slotted optos side
by side, presumably to generate Gray code or some such to determine which
direction it's going. The output from both optos was poor, never getting
close to zero. I thought it was unlikely that both of them would be faulty,
so I took my air line, and blasted out the gaps, and the slots in the
encoder wheel. When retried, reset proceeded at normal speed, and fully
completed. When I checked the output from the optos again, this time it was
a full zero to 5 volts. A good example of what a problem 'dust in the works'
can be.

That fix gave me a good degree of satisfaction, but the week went downhill
from there ... :-\

Arfa