|
|
|
|
|
At
this time I decide to take a look at whether the DC component
of the vision signal can be better preserved. This is to ensure
the picture doesn't 'grey out' in dark picture scenes, as was
often the case with the AC video coupling found in many black-and-white
sets. The only advantage of AC coupling was that it showed up
aircraft flutter less severely, but that won't be an issue today
with the signal being obtained from an Aurora.
The
blue shows the existing signal path from the video output to the
tube. It turns out I have nothing to do! It is DC coupled already...
C25 just adds some high frequency lift. I now try disconnecting
this capacitor and the picture actually improves. This allows
me to disconnect the wire 'bodge' added earlier to the vision
IF output.
|
|
|
|
|
|
|
|
|
Earlier
on I mentioned how I would like this set to accept not only Channel
1, but also baseband video (on both 625 and 405 lines) and sound.
This will enable me to view my old collection of VHS 625 and 405
tapes at the flick of a switch.
Everything
will be displayed at 405-lines on the screen.
I wanted
there to be no inconvenient re-plugging involved so have come
up with this system. I was lucky enough to find a 4-pole 3-way
wafer switch in my stock. The whole thing rather depends on this.
The
'CNV' and 'MOD' refer to the functions of my old 'Domino' standards
converter which, for years hadn't been doing very much. It was
superseded by the 'Aurora'.
|
|
|
|
|
|
|
Here
is the Domino on its side. It is to be permanently mounted inside
the set to handle the 625-to-405 conversion (when needed). This
is effected by adding a central mounting bolt which, with a nut,
will secure the unit to the cabinet floor.
|
|
|
|
|
|
|
|
|
The
new system selection controls will replace these two cardboard
panels Actually this is one piece of cardboard mounted behind
two orifices.
|
|
|
|
|
|
|
This
new aluminium panel will replace the cardboard, mounted behind
the two orifices. I made this up from two smaller pieces of aluminium
I had to hand.
The
holes, from left to right, will take the Ch1 aerial input, the
video and audio inputs, the system selector switch, and - on the
right panel - the timebase amplitude and hold controls.
It
will of course be earthed.
The
AC/DC set chassis will be powered through a new isolation transformer.
There will be a true earth reference adopted throughout the system.
|
|
|
|
|
|
|
|
|
I now
prepare the mounts of all the various units. Here the cabinet
is placed on its side while a thickening MDF panel is glued in,
weighed down by a couple of lead acid batteries!
This
thickening panel is needed to take one of the new mounts of the
Bush TV chassis...
|
|
|
|
|
|
|
...
which sits on the floor to the right - next to the other gubbins.
There is plenty of room in the Baird console cabinet - all wasted
in the original set!
|
|
|
|
|
|
|
|
|
Unfortunately
during the test fitment I lose my balance (thank you Parkinsons!)
and fall against the TV screen unit standing on the floor nearby.
I badly
jolt the tube, but this appears to have survived. The upshot is
this scratch, which will have to be later repaired.
|
|
|
|
|
|
|
Previously
I had constructed this bearer from timber to hold the rear of
the tube.
There's
no Baird chassis there now to do this job!
|
|
|
|
|
|
|
|
|
This
pot in the RF/IF tray is used to control the vision interference
limiter. Under modern closed circuit conditions it will become
redundant, so it is now removed.
Doing
this will also take a little of the load off the HT.
|
|
|
|
|
|
|
Attention
now turns back to the cabinet.
I want
to improve the appearance of the speaker grille, which in the
Baird was expanded metal.
Here,
some fine nylon netting is being soaked in hot coffee to make
its colour a little warmer. What we can actually see is the round
inverted plate used to hold it down in the bowl...
|
|
|
|
|
|
|
|
|
A layer
of the netting is then applied over the original expanded metal...
|
|
|
|
|
|
|
...
then a second layer! All this is held together with Scotch spray
adhesive - the can is seen at the top.
The
effect is like a vintage speaker fabric. The real thing sadly
now seems to be unavailable.
The
speaker board is now mounted back in the cabinet behind the wood
spars.
|
|
|
|
|
|
|
|
|
Back
now to the electronics, and the scan coil leads are extended so
they will reach the chassis in its new home at the bottom of the
cabinet.
The
EHT lead, tube base leads and tube earth are extended too.
|
|
|
|
|
|
|
Time
to consider the powering arrangements. The various units are all
to be powered through this isolating transformer and earthed.
This
feeds a distribution block, into which the units will be plugged.
|
|
|
|
|
|
|
|
|
The
tangle of new extension wiring is getting a mite confusing on
the bench!
|
|
|
|
|
|