labels are added. Next, to switch it on !
a raster of sorts... My guess for the position of the ion trap magnet
has proved almost spot on. Without this, I'd have got no raster
At this stage, basic
checks are done on the tube heater voltage, the HT, the tube's 1st
anode voltage and the sound output valve's cathode voltage.
The Aurora converter
is plugged in and the set tuned in. After first setting the channel
knob adjuster for maximum sound, I am now adjusting the two coils
on the RF input stage for maximum vision.
I'm not a believer
in doing a full IF re-alignment on televisions unless it is clearly
necessary. This is because damage to the little cores can so easily
occur. With experience, it's possible to judge the state of alignment
quite accurately from close inspection of the test card; also by
looking at sensitivity, and checking for absence of interference
between the vision and sound signals.
(on the trader sheet) is set up for maximum width and general picture
health. A large mirror the other side of the bench is useful during
operations like these...
a set is being run up for the first time, it's a good idea to gently
waggle the valves to check the contacts are reliable. Despite having
been cleaned and lubricated beforehand, sometimes they're not !
after a few gentle circular motions (don't bend the pins!) any disturbances
tend to disappear.
One thing worth checking
is that the focus magnet is nicely centered about the the tube neck.
You can adjust the position of this bracket to ensure this. I should
have done this before, but it's only a five-minute job to whip this
off and do it now.
EHT checks in at 7Kv and since the U25 rectifier was a non-standard
part, its heater glow colour is now checked - it looks very comfortable.
picture and sound is obtained. The ripple toward the bottom of the
picture is a camera artifact.
Now the set will be
run for four hours continuously to 'wake up' the tube and generally
settle everything down.
Next to tackle the
inevitable 'niggling' faults. The line hold control cuts off altogether
at one end of its travel. It proves too difficult to repair internally,
so is replaced by another vintage pot - first stuffed with Waxoyl
There's also an unpleasant
jitter on the line timebase which causes ragged edges on the Test
Card. It seems to improve as the set warms up. This is improved
by replacing the 2M2 grid leak/load across the sync separator input
with 470K and then abolished by fitting another PL38 line output
A habit of mine with
these sets is to to check the operating temperature of the line
output transformer after it's been running a while.
The set is switched
OFF and a finger pressed firmly on the top of the laminations.
This tells me whether
the laminations are in good condition. These are - the transformer
is only gently warm.
Another little touch
I always do is to paint the top of the laminations matt black for
better heat radiation.
Let's now look at
The picture mask and
armour-plate screen glass are cleaned. The mask has some light crazing
but once cleaned looks almost perfect. It is being left as it is.
The rubber insulation
on the wire connecting the chassis to the internal cabinet screening
foil is cracked and perished - as it usually is.
It suffers from the
heat of the dropper nearby.
It is replaced with
new black rubber-covered wire.
Fortunately this cabinet
is already in quite fair condition. It is now polished with soft
wood wax, applied sparingly - important this - and with some preparation
beforehand using P.O. Polishing Paste No. 5.
The knobs are also
cleaned. It's possible to improve the appearance of their markings
by lightly scraping off the top layer of the gilt with a small screwdriver
blade, under a magnifier.
When the cabinet is
offered up to the chassis and slid back to its final position, it's
important to ensure that the tube front face exactly abuts the back
of the mask.
the earlier tube position set up on the bench will have to be changed.
The mounting bracket
and rim band is loosened - and the tube pushed as far forward as
possible. Then the cabinet is withdrawn and everything tightened
Here the fastenings
are loosened before the cabinet is slid back.
necessary job at this point is to ensure the line and frame hold knobs
are adjusted on their shafts so that their faces are flush in their
holes with the cabinet tightened up on the chassis.
this one thing I have forgotten to check..
The on/off volume
pot shaft is sitting too high for the knob to be inserted and tightened.
This means I'll have
to take everything out of the cabinet again. But it's all bolted
together now so I think I'll leave this for tomorrow...
dinner I am filled with more energy and enthusiasm ! The pot
position is soon put right and the back goes on.
However I have had
to take both securing screws out to get the front knobs in through
their holes. Then I had to insert the screws back into the knobs
through the bottom of the set. This was a bit of a fiddle...
Purists may hold up
their hands in horror but I am using new 2BA screws and large, shaped
washers to secure the back. The washers are ground to produce flats
on one side so they will correctly match up to the inner edge of
In my opinion it is
far more important that the back is held properly on the cabinet,
than to re-use the old fasteners in homage to originality.
When putting on the
back of a TV22, don't forget there are also two screws (with washers)
Anyway, let's switch
it on and have a look. Here's Test Card 'C' plus some reflections
from the fluorescent lights !
This was taken after
I had loosened off the centering magnet and bodily shifted it about
- before re-tightening.
Note the rather wasteful
'Double-D' shaped picture mask. The earlier TV12 had a more rectangular
There was one other
thing to attend to though... something I've noticed this in other
TV22s... the picture height expands by an inch or so over the first
half hour or so from switch-on.
After a lot of head
scratching and component substitutions, this was improved by replacing
all the high value resistors in the frame timebase, despite
their values originally measuring OK.
Some believe there
may also be a LOPT dimension to this, with changes occuring in internal
insulation leakage in the overwind as it heats up.
the output of the frame timebase revealed that the expansion was
mirrored by the increase in voltage across the frame scan coils
but not across the primary winding of the frame output transformer.
Cooling the coils with a fan seemed to help, even though they are
not running warm to the touch. Weird! (I'd already confirmed the
frame output transformer primary winding resistance remains steady,
and is the correct value, so shorted turns are unlikely there.)
So a small fan was
installed, powered from a rectified dropper section, and this was
arranged to blow across the scan coils, thence into the LOPT housing
via a new hole punched in its inner side.
Further knowledge about this problem has since been gained. It has been established
that, in the main, this is being caused by damp (or undried replacement
varnish) trapped in the windings of the LOPT, reducing both the line scan amplitude
and the EHT. This shows as a dimmer, softer picture and an increase in height. The EHT problem is often accompanied by an excessive dependence of EHT on beam current.
practice nowadays is to pass a current of around 50mA through the
overwind for several days at the time of service, driving the moisture
out. This technique can also improve the performance of LOPTs where the overwind has already been varnished or repitched. The final step is to seal the windings generally with an anti-corona aerosol (such as from RS) before
more moisture can be absorbed.
this time the U25 fitted as EHT rectifier was returned back to the
original EY51, now that I have them back in stock.
re-gunned aluminised 9-inch cathode ray tube was also tried now,
obtained from a French supplier. This turned out to have a faint
shadow in the centre of the screen and is being returned to France
this is one of the best TV22s I have ever come across. The cabinet
is virtually pristine. I hope that in restoring it I have now made
it better still.
And here's the owner
and very valuable customer David White come to collect.
But has Cinderella's
coach turned into a pumpkin? No, this is a fine G.E.C. BT 302 which
is to be the next project.
Please note I am unable to enter into any correspondence if you are servicing your own TV22, nor can I supply spares. Thank you.