I am now Annoyed [Re: Old oscilloscope help: ideas sought]

[Tony Duell]

> 
> > 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.

That does not suprise me. In fact, even if the rectifier valves were 
indirectly-heated (separate heater and cathode) it would be quite usual 
to have a separate heater winding for the rectifier and to connect the 
cathode to one side (or the centre tap) of that winding. A number of 
rectifier valves were not rated to withstand the full HT (B+) voltage 
between heater and cathode.

> 
> >> (There are some 12V-heater tubes, but they all have centre-tapped
> >> heaters.)
> > I assume things like 12AX7s...
> 
> 12AU7, from memory - again, they're at home and I'm not.  (If you have

There are 3 common double tridoes with centre-tapped 12V heaters -- 
12AU7, 12AT7 and 12AX7 to you. And ECC81, ECC82 and ECC83 to me :-)

> my emails from the summer, they include a valve complement list.)
> 
> > 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).

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.

> 
> > 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

It's more normal to have 'E's and 'I's arranged alternately.

> 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