The underneath of
the LOPT is arrowed. It's a good idea to make a note of the connections
now, before it's removed.
It will be seen that
the HT smoothing choke has been temporarily detached from where
it normally lives (hiding the LOPT) to give better access.
Here is the line output
transformer removed from the chassis. Close inspection reveals some
surface rust on the laminations but nothing too bad.
The EHT cable (to
upper right) is chopped off and will later be replaced.
What follows is optional
and holds dangers of damaging the transformer for the unwary. However
I always do it to ensure that the transformer will later run as
cool as possible.
First, the remains
of the old mounting sleeves covering the horizontal laminations
is removed. Then the transformer is put in the oven at no more than
200ºF for half an hour to soften the pitch. The pitch is then
gently flaked off with the fingers...
care not to break the very fine wire connections to the EHT overwind
(arrowed). If you do this you have a serious problem !
Be very careful
also if you pick out pitch from around the inner coil former
- only visible when looking down from above the top of the transformer.
Dr Hugo Holden proposes an alternative, gentler method. The old and cracked pitch can be removed by immersing the LOPT in a white spirit bath over a period of several days, which can then be followed by varnish or a light coating of anti-corona spray.
Incidentally the diagram
seen here underneath came from Andy
Beer's site which includes much useful information on the TV22.
You might spot I've annotated resistance readings on this diagram.
At this stage a quick runaround on the tags with the Avo checks
that all is well.
Unless you have a
serious case of rusty laminations, it's not necessary to completely
disassemble the transformer or remove the lamination stacks. But
in any case WD40 is seeped into these to keep them well preserved
for the future. Then the horizontal laminations are wrapped with
tape. This ensures that the expandable neoprene sleeves which are
added afterwards won't get perforated by any sharp edges.
Finally, the transformer
is sprayed lightly with a modern anti-corona lacquer. It should
now be good for many more years of reliable service.
In the meantime, the
various chassis parts have been cleaned down. Now it's time to turn
our attention to the mains wiring.
In this example, it's
actually still in quite good condition but nevertheless it has to
be replaced under my inflexible creed which says that mains wiring
must always be replaced.
to come first, with reliability and originality more
or less tied for second place...
Naturally, the dropper
housing has first to come off. However I can't gain access to its
securing nuts underneath unless I also unhitch the vertical form
and height potentiometers, along with the screening panel that surrounds
the frame timebase valve area.
The old 2-pin mains
connector has to go too I'm afraid... It's replaced by a little
coated aluminium panel and grommet secured through the original
rivet holes. Otherwise it would be possible for the chassis to be
live (rather than neutral) in the future.
The dropper housing
is re-mounted and new mains cabling installed. This runs to-and-from
the switch (not seen here - underneath at the front).
The cables are shrouded
with neoprene rubber sleeving where they pass near the dropper and
frame timebase valve, for heat protection.
A new Y-rated capacitor
is connected across the mains and araldited into position. This
is the small block seen to the right of the dropper housing.
up the new cabling at the mains switch end, the switched potentiometer
is dismantled and injected with Waxoyl to ensure a long, crackle-free
future. Experience has taught me that Waxoyl gives a more durable
result than Vaseline in this application. Above all, don't use WD40
here - it can dissolve the carbon track's surface !