1 Mar
2007
1 Mar
'07
10:48 a.m.
The type of those valves will give you a good
idea as to the voltage
required of course.
Yes. I need to look them up; they don't appear in the reference book I
have at ready hand. ("Had", actually; it's at home and I'm not.
That's also why I don't give the valve type number here.)
Almost certainly the EHT rectifier vavles are
directly-heated,
Yes. All the rectifier valves (including the B+ one) have filaments
rather than heaters. (There
are some 12V-heater tubes, but they all have centre-tapped
heaters.)
I assume things like 12AX7s... my emails from the summer, they include a valve
complement list.)
Well, even with a 40W bulb in series, I would expect a transformer with
no load on the secondaries to give almost full output if there were not
shorted turns.
My first concern is that the primary voltage is
very low -- in other
words this transformer draws excessive input current even when
unloaded.
Yes - as I mentioned back in the summer. This is just further
confirmation of it. I was using a 40W light bulb in series with the
primary, as a current limiter, which is why the primary voltage was 25V
instead of ~120V. The bulb was glowing (not quite full power, but
close). This suggests to me shorted turns, probably in
the HV winding (which
would alos explain the very low outptu voltage there.
I agree; this is why I suspect the HV winding of being the culprit.
You might consider rewinding the original
transformer, although
getting the insulation to withstanda a few kV would be 'interesting.
Quite. It also would be "interesting" to get it apart far enough to
rewind. It's a laminated core made up largely of E-shaped pieces, and Actually, come to think of it, looking at your
(natural enough) use of
"valve" where I'd write "tube", I'm curious - are CRTs called
CRTs on
your side of the pond, or something else (CRV?)?
No, we call them 'Cathode Ray Tubes' too (at least unless you're talking
about the RAF 60 years ago ;-)).We also have travelling wave tubes,
photomultiplier tubes, nixie tubes, and so on. Also a 'television tube'
is what an RCA manual would call a 'kinescope' -- that is a TV receiver CRT
Other terms that are relevant and different include :
UK US
HT+ (High Tension Positive) B+
LT A supply (heater supply)
EHT (Extra High Tension) HV (high voltage to the CRT, etc)
Anode Plate (of a tube)
Also, in the UK, CRT electrodes are named 'cathode', 'grid', 'first
anode', 'second anode',...'final anode'. I believe you call them
'cathode', 'first grid', 'second grid',...'anode'.
Oh, the comment about the RAF perhaps needs explaining. In WW2, the UK
armed services all had their own valve numbering systems. The RAF one had
codes like
VUxx (Valve, Unidirectional) for rectifiers
VRxx (Valve, receiving) for small-signal valves
VTxx (Valve, transmitting) for transmitter valves -- this one caused, and
causes, endless confusion with the US Services 'VTxx' designations, here
standing, of course, for 'Vacuum Tube'. The numbers are not the same.
and
VCRxx (Valve, cathode ray) for CRTs.
To tie this in to classic computing, I believe the original 'Williams
Tube' store used an ex-radar CRT (easily available after the war) called
a VCR97.
-tony