4 Jul
2006
4 Jul
'06
3:29 p.m.
Welcome to the world of old tube equipment. :/
Uh, thank you. I guess. :-) (I actually started hacking electronics
with vacuum tubes, well before I did anything significant with
semiconductors. Back in the days when you could find large numbers of
vacuum tubes thrown out in the guts of consumer electronics.)
The symptoms you describe are not unusual and it's
most likely a
short in the transformer. If, as you say, only some of the tube
filaments were dark,
That's not quite what I meant. I looked over, and all the tube
filaments I saw were dark, but that was only about three of them, and I
didn't look to see whether the rest were or not before diving for the
power switch. So I can be certain of only some of them, but my
observations are consistent with it actually having been all of them.
In equipment of that sort, shorted caps don't
usually present such a
degree of problem to the transformer. The vacuum-tube rectifiers
have some hundreds-of-ohms of plate resistance, as well as maximum
emission (current) limits, and act as a limiting impedance for
shorted/leaky caps.
That's what I'd expect. I'd expect to see red-hot plates on the
rectifiers before I'd expect the transformer to go - especially a
transformer as big, and, by implication, with as much excess capacity,
as this one.
If it's any consolation, there probably wasn't
anything you could do
to avoid the failure.
That's reassuring, yes. Thank you.
I pulled out the schematic for a Stark OSK-4, a very
basic
vacuum-tube 'scope, probably similar in category to the DuMont.
If it helps, the tube list for this thing (aside from the CRT itself)
is:
12AU7 x8 6J6 x2 2X2A x2 6AQ5 x2
6Q50 x1 5Y3GT x1 0B2 x1
The 6Q50 might be 6Q5O or 6Q5Q instead; there's a dark mark at the
lower right of the last character, but it's not clear whether it's an
intended part of the printing or a bit of dirt. The tube actually in
that socket is an 884; "or 884" is penciled next to the socket.
Here are some observations which may (or may not) be
of assistance in
your situation, if you are RE'ing the power supply: [...]
Noted. Thanks. I don't know whether they'll be useful, but I'll keep
them in mind.
If there's no rush and you're willing to wait
on a possibility I can
poke around the radio museum here in the next couple of weeks to see
if there's a junkered/junkable DuMont (let me know the model number).
"TYPE 304 H". That's the closest thing to a model number I could find.
We have piles of old vac-tube scopes that we should
get rid of and I
know I've seen a DuMont or two. Shipping (cost) would be from
Vancouver.
Well, a lot of the work I'll need to do I'll still need to do even if
you can dig up a spare for me. And it's unlikely to take less than a
week, so....
If you do find a junk one, I'm tempted to ask if you'd be willing to
send the whole thing, as a parts unit (most notably the tubes, at least
after the power transformer).
/~\ The ASCII der Mouse
\ / Ribbon Campaign
X Against HTML mouse at rodents.montreal.qc.ca
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B