6 Jul
2006
6 Jul
'06
1:13 a.m.
So either the
primary is very sick, or some secondary winding is
shorted and is loading the primary.
It sounds as if your assessment is correct. :(
Since gas reference tubes like the OB2 do best when
the supply
voltage is substantially higer than the operating voltage of the
tube, I'd say that the winding on the plates of the 5Y3 are probably
more like 150-0-150 VRMS.
Ooh, yes, I forgot I was measuring plate-to-plate voltage, not
plate-to-centre-tap voltage. So the voltage I was seeing is only about
half what it'd have to be, even ignoring losses in the 5Y3GT and the
"substantially higher" you mention.
Your next logical step is to disconnect and remove the
transformer.
Yes, I think I agree. It is sufficiently dead in place that even if
it's something fixable I'll still have to take it out to deal with it.
Rather than unsoldering it, I'm going to assume
that this is like
most old equipment and there's some slack in the leads.
There is. I wouldn't unsolder it either, but my principal reason is
that most (all?) of the connections have the wire wrapped around before
soldering until it's reasonably secure mechanically *without* solder.
Good construction technique in most respects, but a pain when it comkes
to desoldering. (Especially when the connection is not very
accessible, which is the case for at least half of them.)
In order not to put too much strain on the sockets and
components,
I'd recommend that you clip the leads perhaps a half-inch away from
their ends, tagging the "stubs" so you can see where the wires
connect when it comes time to connect up a replacement.
Actually, I would more likely just tag each wire from the transformer
(probably with a simple serial number), and write down where each tag
goes (things like "V9 pin 5" or "C12 positive side" or
"chassis") - and
cut the wires as close to their connection points as I can easily
manage.
There is a very very slim chance that one of the lead
wires has had
its insulation degraded to the point that it's contacting the shell
of the transformer and shorting things out.
None of the insulation looks degraded, so I consider that, indeed, a
very very slim chance. I sha'n't overlook it, though, and will check
for evidence of such a thing when I crack the transformer case. (Given
how electrically broken the thing is, I'll probably have to open it up
just to tell which wires go together - there are a few I'm not sure of.)
So after you get the transformer out of the scope, you
may want to
open it up (if it's a "clamshell") type and have a look.
I'm not sure what a "clamshell" is, here. This transformer has metal
(presumably steel) sheet laminate for the core, metal sides enclosing
the windings, and bolts through the sides and the lamination layers to
hold it all together. It's a common design for vacuum-tube-era power
transformers, in my (admittedly limited) experience. And it's big; my
"ten-kg" upthread was a somewhat flippant estimate, but it wouldn't
surprise me if it's about right.
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