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Even
so,it wasn't much to look at, but at least it WAS a raster.
I eventually
twigged that the tube wasn't cut off as a fault... the Brightness
was simply turned down!
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At
this time, EHT weighed in at 8Kv. Later on, tweaks and a steadily
de-gassing tube improved this to 10Kv.
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As
for getting some sort of picture, I'd need a suitable signal.
From
the Tuning Indicator, it looked like this would have to be a Channel
4 or 5 signal.
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This
is what I saw on Channel 4. Hopelessly out of alignment though,
both picture-wise and tuning-wise.
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Always
a good idea with these Bushes is to take out the two subsidiary
user tuning cores and inspect them for condition.
Here,
I'm removing the one in the middle. This tunes the anode side
of the first RF stage.
The
one to the left of this tunes the grid side of the first stage,
at the aerial input, and only has a broad effect.
The
spring-loaded button to the right - the 'main' one with the scale
- adjusts the local oscillator frequency. It is supposed to be
set to give maximum sound. If the rest of the alignment is correct,
this should automatically also provide the best picture.
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Well
what do you know.. The check was worth it. The left hand core
is mostly missing.
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I wonder
if the rest of the core is still inside the coil?
Let's
have a poke through with the screwdriver.
Nope...
it comes straight out the other end without any sign of core.
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What
a shame I have now given all my spare TV22 chasses away... might
have yielded a core.
Never
mind. I make one out of a piece of another core, stuck to the
old one with epoxy and all wrapped up with paper tape.
It
doesn't look the business, but it works! I can now re-tune all
the adjustments to Channel 1.
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Want
to see the picture? Wait a little longer. Here is a 'dogbone'
resistor which measures only slightly low but looks generally
distressed. It feeds the screen grid of the line output valve,
the part of which also doubles as the line oscillator. It is replaced.
Talking
of the line stage, the 'line drive' level also has to be set up
on this circuit. This is duly done.
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I have
to say I'm not hugely impressed with the picture on the screen.
It is exhibiting a deficiency in the LF video response, as evidenced
by smearing on the 'letterbox' on the Test Card.
This
is bad news. Nothing in the video amplifier seems to be causing
it. I am reluctant to consider a full IF realignment... thinking
of stuck and broken cores etc. It was all very well in 1953, but
now...
So
I do something really naughty as a temporary solution.
I solder in a short piece of lead to the final IF stage anode,
to provide some capacitance to alter its tuning.
You
can see this taped to the upper side of the chassis.
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While
this has a beneficial effect, it is clearly a bodge that'll have
to be put right later.
After
ten hours (so far) of 'burning in', the picture is still steadily
improving.
Another
remaining fault is a tendency of the frame to bounce at some positions
of the height and linearity controls. I'll be looking into this
next.
Then
maybe to try fitting the Mullard tube out of my Baird Townsman,
if it proves practicable, to compare it with this one.
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The
frame bounce was cured by changing this ECL80 frame valve... twice.
The
first replacement I tried also proved faulty. These ECL80s are
not the best of valves in my experience.
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The
Bush chassis - to top - now meets the Baird chassis it will replace.
Somehow
I'm going to have to mount the Bush in the Baird cabinet. The
main mass of this cabinet is not seen here.
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I had
previously fitted a non-standard Mullard tube to the Baird and
I had high hopes for this.
However
the tester showed it had an intermittent partial short on the
heater, so that's another rare early round tube that will have
to be scrapped.
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Here's
an old treasure found in the bowels of the Baird that I intend
to re-use. It's a valve audio amplifier complete with bass and
treble tone controls.
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Two
changes on the Bush chassis are needed to accommodate this.
On
the left, a 3 ohm power resistor replaces the connection to the
Bush's original speaker. On the right we see the new sound output
socket. This is connected into the volume control.
The
amp uses a Belling-Lee 'aerial' socket for the audio input, so
I have stuck to the same convention. This will allow the convenience
of using a simple aerial lead to connect up.
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