Michael A. Terrell wrote:
Trevor Wilson wrote:
"Sylvia Else" wrote in message
...
Whatever happened to circuits that just contained a couple of valves?

**There never were any "circuits that just contained a couple of valves".
When they first arrived, TV sets were mindbogglingly complex devices
compared to anything that preceded them (in domestic appliance-speak). They
were also fabulously unreliable. You could figure that the average TV set
would require several repair jobs every year. Your incredibly complex, LSI
controlled, TV set is likely to be vastly more reliable. You've probably
found the first fault it has ever had.


It sounds like they only sold crap in Australia, and that you've
never seen the very low parts count in a Muntz TV.

My parents had three service calls in 15 years. Two of those were
due to lightning taking out the front end in the VHF tuner. The third
was a bad electrolytic in a voltage doubler that took out a fusible
resistor. That isn't a couple times a year.



It must be thirty or thirty five years ago that my family in England got
one of the early fully transistorised Philips colour televisions, with
teletext. This was our upgrade from B/W. We rented it, rather than
bought it, which was just as well, because it frequently broke down.
Indeed, the first occasion was within days of its arrival, with an
intermittent fault that the service company never did track down[*].
Often repairs involved fixing dry joints.

So Trevor's comment does fit my own experience. Televisions have become
more reliable. But I wonder whether that's because of improved
construction and quality control, rather than because of the circuitry
now in use. If individual components are very reliable, and they're
fixed properly to the circuit board, then the result can be reliable.
That doesn't mean that the design doesn't use an excessively large
number of components.
[*] The fault had the dual effect of killing the sound, and making the
picture about twice as wide as it should be. Years later, I obtained the
schematics for the set, and it was quite obvious where the fault had to
lie. I can only assume that the technicians who came to fix it either
didn't understand the circuit, or just couldn't be bothered. After they
fiddled with the set a bit, the fault would go away. Later I found that
a good thump on the cabinet would work just as well as calling the
technician.

Sylvia.