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Transformer failure mode
Hello Folks,
Just a brief note from Allanson's perspective regarding incidence of
transformer failures. They fail in this order from most prevalent to least:
Moisture
Corona
Heat
Vibration
Sad to say, we are getting more and more returns which, when analyzed, are
found to be soaked to the core. In some batches of returns we find over
half have been wet. Back to more long-term observations, it is our
experience that conditions which cause excess corona are much, much more
damaging than anything else. Most of you know that corona tends to
chemically alter the environmental surroundings to produce acids, etc. which
eat up insulation. Then transformers short between layers or pot to ground
on the can.
Most reputable tranformers these days are well-insulated for resistance to
heat. As long as the tx is not contained in a non-vented cabinet or box,
(especially enclosed in a sunshine-baked window) things usually tend to go
quite well. Excess input voltage does cause heat build-up but we find
incidence of failure from these circumstances much less than insufficient
input voltage which tends to cause the secondary coils to work too hard to
drive the intended tube load. (Same high-corona situation).
As for vibration, it occurs so infrequently, we tend to ignore it. I just
included it to be 100% thorough.
What this leads us to recommend is to never knowingly put too large a load
on a transformer. However, doing something such as attaching only 50% of
rated load is not only uneconomical, it does eventually damage the tx. For
underloading, use common sense. 20% ??? Okay. 50% ??? You're taking a
bigger risk.
Well, that's it for this post.