"carneyke" wrote in message
...
Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired and if the spec's were avaialbe (24 Volt
center tapped 10 Amp for example) it could be substituted. Aside from
the shielding I can't see any reason it can't be subbed. There is
plenty of room too. I have found several 10 amp tranfromers that are
similar in size. I don't want to buy the wrong voltage transformer. I
have schematics for similar models and it doesn't show voltage /
current ratings, just part numbers. I asked the JVC part supplier if
they could get specs on the transformer, they haven't returned the
information. Thank you in advance !

Generally, you can take the working voltage marked on the main filter caps,
reduce it by about 1/4 (though note that there are some on here who would
dispute that level of derating) then divide the result by about 1.4 to get
an RMS secondary voltage for the transformer. So, if the caps are rated at
say 63v, it is likely that they have no more than about 45 - 50v across them
in normal use. Dividing this figure by 1.4 - or multiplying by 0.7 - gives
you an RMS figure of around 32 - 33v. You can get a rough idea of the
current rating by looking at any secondary fuses. These will be usually 1.5
to 2x the expected current draw. If there are no secondary fuses, an idea
can be obtained from the input power rating shown on the back, and the
voltage ratio primary to secondary. An efficiency of 90% or better can be
assumed for the transformer.

Obviously, it's all a bit more complicated than that in truth, but you can
use it as a good 'rule of thumb' that I have used for many years to do just
what you are trying to do.

You might try looking at the existing transformer when you have it out, just
to see if the thermal fuse legs are visible, or brought out to tags. In
either case, it can then be bodged with a TEMPORARY short to measure the
transformer voltages.

Arfa