chassis is reassembled, every original fastener is polished
up to shine - with steel wool.
The scan coils
are given a continuity check and the capacitors and resistors
attached to them are replaced. Although this is not a 'hiding
new capacitors in old' restoration, nevertheless the new
capacitors are hidden in black neoprene sleeves so they
will merge in better...
The EHT smoothing
capacitor is checked and passes with flying colours. This
original feature will be used again.
The EHT heater
transformer is megger checked for isolation of the windings.
It proves to be in excellent condition.
The line output
transformer is meter checked and seems fine. It's carefully
cleaned - many of the connections are very delicate - and
then sprayed with a moderm anti-corona lacquer - to ensure
a long life in the future. This appears to be a later type
'ferroxcube' (replacement?) transformer. It will be interesting
to see later if the associated component value changes recommended
by Baird have been carried out.
EY51 EHT rectifier is replaced as a matter of course.
of pots that operate the volume, brightness, focus and contrast
is now tackled. All the pots are cleaned, then opened and
stuffed with waxoyl. I find this treatment successfully
refurbishes 95% of old pots and should ensure decades more
of noise-free life.
WD40 on a pot track, or it can get dissolved !
morning I decide to have a go at reforming the electrolytic
capacitors before getting to work in earnest below decks...
I built up
this little reforming box a long time ago to Paul Stenning's
design. The meter shows a leakage current of 20mA. Although
this is just the start of the reforming process, this is
a huge amount and doesn't bode well.
A little while
later it becomes clear that reforming isn't going to be
the way to go on this set! Instead, I'll take them all off,
remove their insides and hide new electrolytic capacitors
is a row of pots at the rear of the chassis - the 'occasional'
rear controls including the notoriously unstable (on this
set) line hold. The one on the end I thought was the white
spot limiter but - looking at the set's card back - claims
to be another 'width' control. I'll sort this out later. For
now, I replace it with a similar pattern replacement (and
parallel resistor) to get its value right. Its wire winding
had been clearly broken. All these controls are then waxoyled.
you'll recall I had built up a complete set of good valves
for this set. These are now cleaned. Glass cleaner is carefully
used, so as not to attack the valve markings. The pins are
cleaned and left coated with a thin film of WD40 to discourage
future oxidation. Black bases are dressed with Amor All so
they now shine...
blocking oscillator transformer turns out to have one o/c
winding. Here it is before cleaning. This transformer is
removed and the inside from a spare TV22 transformer (previously
rewound by Ed Dinning) is substituted inside its frame.
This way, the 'new' transformer looks exactly like the old.
2-pole mains connector is today only legal for 50 volts
so has to go. It's replaced by an insulated aluminium panel
bearing a sleeved grommet, through which passes a new mains
lead. In this way, it can be positively ensured that the
chassis is always connected to mains neutral, whereas before
it could have on occasion been live.
All the more
necessary, because the toggle of the nearby mains switch
is only isolated from chassis by a thin paxolin ring. Now,
to be absolutely sure of safety, the switch body is earthed.
work now on re-stuffing the electrolytics. The replacement
capacitors have arrived this morning from RS. The first
one is a real toughie... it's remarkably hard to drill and
scoop out the insides.
The new capacitor
fits snugly inside the old for easy re-connection..
has kindly found me a suitable replacement dropper for this
set. With one subsidiary resistor, it will function as an
This is what's
so nice about the vintage television business. Everyone
does their best to help everyone else. You can visit Andy's
mess is the stack of surge limiter resistors going into
the four rectifier anodes - all in parallel.
Most of these,
along with every winding on the old dropper, are found to
be burnt out. This old set must have undergone a red hot
emergency when it finally gave up the ghost before !
replacement. I have made up a bus bar for easier mounting
at the commened ends of the resistors. The original 75 ohm
resistors have been replaced with 82 ohm for slightly better
buffering, although this value is still less than the 100
ohms shown on the schematic. In this and various other respects,
slight differences from the schematic have been found.
At this stage,
the capacitor across the mains is replaced with a modern
'Y' rated component. Some of the original capacitors are
still to be seen in this picture. They're to be tackled
which, here's one of the dreadful Hunts capacitors. This
one was in a safety critical position but nevertheless has
'melted' over a long period where a wire was pressed against
it. Either they do this, or more often their cases simply
break up. Hunts capacitors should always be replaced, in
whatever condition they are in.