Re: Dec 2 TV 0
- From: Terry Casey <k.type@xxxxxxxxxxxxxxx>
- Date: Sun, 6 Dec 2009 15:56:47 -0000
In article <hZSdnREvo9W_XoTWnZ2dnUVZ7qQAAAAA@xxxxxx>,
nospamclayton@xxxxxxxxxxxxxx says...
This was an appalling scam in the 60's - the TV's boasted dual standard, but
most of the circuitry for 625 lines was not there!
Typical time-line for one manufacturer (Bush)
TV105 series: (1961) Largish rectangular buttons marked 405 & 625 under
the 4 VHF tuner buttons. 405/625 buttons connected by rods to a paxolin
plate (only) fixed via a central pivot, so that one came out when the
other was pressed. The chassis was 405 only
TV115 series: (1962) TV105 dummy buttons replaced by a large horizontal
lever which operated the timebase system switch. 405/625 timebase, RF/IF
section entirely 405.
TV115L series: Late variant of the TV115 with dual standard IF strip, so
chassis now fully dual standard except for the UHF tuner.
TV125 series: (1963) Internally identical to the TV115L with external
design change - VHF tuner rotated through 90 degrees with buttons now
vertical (tuner position remained at bottom of the cabinet). Four dummy
UHF buttons at the top with matching 405/625 buttons arranged
horizontally in the centre.
TV125U series: First full 405/625 set released.
Conversion kits were 8 guineas for the '115L & '125 (UHF tuner only but
the '125 kit included a little 'U' label to stick on the back to modify
the model number!)
Fifteen guineas got you the '115 kit which also meant replacing the IF
strip.
As all these sets were marketed as being 'fully convertible', there was
a kit for the '105 series produced, though, at around £30, I doubt many
were sold! All these prices, of course, excluded labour costs!
Note that, in those days, new models were announced at the annual Radio
Show (later replaced by individual trade shows) held during the summer,
so the dates quoted above relate to an autumn release.
Thus the TV125 series was released about 6 months before BBC2 started
and was produced in two versions, with and without the UHF tuner,
although I can't remember if there was a delay releasing the TV125U. The
price differential - surprise, surprise - was eight guineas!
Of course, as BBC2 was only initially available from Crystal Palace (and
relays) all of the unconverted sets elsewhere in the country got
progressively older while they were waiting, which must have made
conversion costs increasingly unattractive ...
The other problem was that at 625 lines the PL 85/805 line output valve used
to blow fairly quickly...
I'm confused here or, at least, I think you are!
The PL81 line output valve had largely been superceded by the PL36
which, I think all these sets used. I don't recall them having a shorter
life working at 625 lines, though.
I'm sure you're thinking of the PCL85/805 FIELD output valve.
The PCL85 was a very badly designed valve which failed repeatedly. The
replacement PCL805 was better - these tended to have a shortened life,
though, if the cathode bias resistor which had been badly cooked by its
predecessor hadn't been checked and replaced if necessary. (These carbon
composition resistors tended to drop in value quite considerably and
seriously over-ran the replacement valve if not replaced.)
As there was no difference in working conditions for these valves on
either system, there was no difference in lifetime.
--
Terry
.
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