TV and radio clashing signals

On Jun 12, 10:35*pm, "Dave Plowman (News)"
wrote:
In article ,
* *Max Demian wrote:

I remember TV sets being AC/DC in the late 50s/early 60s.Of course the
expression took on an entirely different meaning.
You mean AC/DC radio cassette recorders that worked off AC mains or
internal battery?
Or do you mean something entirely different?

DC mains. Some parts of the country still had that long after the majority
changed to AC. But making sets that were AC or DC was cheaper in valve
days.

There was one village near here that had it's own electricity
generation, and it was DC. Absurdly it was in the shadow of a large
power station.

Bill

" wrote in message
...
On Jun 12, 10:35 pm, "Dave Plowman (News)"
wrote:
In article ,
Max Demian wrote:

I remember TV sets being AC/DC in the late 50s/early 60s.Of course the
expression took on an entirely different meaning.
You mean AC/DC radio cassette recorders that worked off AC mains or
internal battery?
Or do you mean something entirely different?

DC mains. Some parts of the country still had that long after the
majority
changed to AC. But making sets that were AC or DC was cheaper in valve
days.

There was one village near here that had it's own electricity
generation, and it was DC. Absurdly it was in the shadow of a large
power station.
Bill


Watford was 200v DC until 1962, power station was behind
the football club, brown outs every other day.

Thank god we got on to the national grid in time for the winter of 63

Steve Terry
--
Welcome Sign-up Bonus of £1 when you signup free at:
http://www.topcashback.co.uk/ref/G4WWK

In article , Dave Plowman (News)
scribeth thus
In article [email protected],
Terry Casey wrote:
AC/DC TVs were around well into the 70s - the ITT VC200 monochrome
chassis and its successors (up to VC207, I think) - were hybrid AC/DC.

As colour took over, large screen monochrome sets became scarce but I
remember having a sample of a Pye/Philips 19" set with a view to
conversion for a special system very late on in the 70s - and that was
still AC/DC!

Were these still all valve? Or if hybrid, how did they derive the low
volts rail for the transistors?


Jeezz quite embarrassing this!, I spent many years on the Philips G8 and
G11 series and I've bl^^dy forgotten now!.

Wasn't there a winding off the LOPT or something similar?..

--
Tony Sayer

Did they even work on DC?

They must have done - they were specifically advertised as AC/DC and
there were still DC supplies around!

I know that Ilford (Essex, but now part of the London Borough of
Redbridge) still had DC mains in the mid - late 50s, a hangover from the
days of Ilford Tramways when the council decided that if they were going
to provide 600V DC for the trams, they would provide a 200V DC domestic
mains supply. When it was converted to 240V AC I don't know but I'm sure
it wasn't the only place with DC supplies.

I was at school in nearby West Ham during this period and I remember the
extensive street works when the local supply was upgraded from 215V AC
(IIRC) to the standard 240V.

My first 625 line receiver cost me £20 in the late 60s - a brand new Pye
export set in a sealed carton. I modified the sound IF from 5.5MHz
system B to 6MHz system I and added a UHF tuner and probably became one
of the first in the country with a single standard 625 line receiver
when BBC1 & ITV UHF transmissions started at the end of 1970!

It was designed to work on 100/250V AC/DC and had a voltage doubler
arrangement for the lower voltages. The text printed on the rear cover
was in English, French and Arabic!


I remember converting some VHF 405 line set's to 625 UHF but the gain
of the early valve tuners wasn't that good .. when transistor ones came
about .. a remarkable improvement

And yes Cambridge had 200 volts up to the 70's just had to short out a
bit of the mains dropper in most all sets and I could have sworn blind
it was DC too!..


--
Tony Sayer

Dave Plowman (News) wrote:
In article [email protected],
Terry Casey wrote:
AC/DC TVs were around well into the 70s - the ITT VC200 monochrome
chassis and its successors (up to VC207, I think) - were hybrid AC/DC.

As colour took over, large screen monochrome sets became scarce but I
remember having a sample of a Pye/Philips 19" set with a view to
conversion for a special system very late on in the 70s - and that was
still AC/DC!

Were these still all valve? Or if hybrid, how did they derive the low
volts rail for the transistors?


It just happens that I un-earthed the Service Manual for the ITT VC207
chassis (August 1973) in the cellar recently and, fortuitously, didn't
throw it out!

All of the low level circuitry is solid state and operates off a 20V
rail derived from a winding on the Line Output Transformer.

The video output transistor and sync separator are fed from the main HT
rail - all pretty much what I would have guessed - but the one thing I
would probably have overlooked is the varicap tuning voltage for the tuner.

The 12V supply for the tuner is derived from the 20V rail via a
potential divider but the varicap supply - 33V stabilised - is fed from
the HT rail via an 18k 6W resistor.

--

Terry

In article ,
tony sayer wrote:
Did they even work on DC?

They must have done - they were specifically advertised as AC/DC and
there were still DC supplies around!

I know that Ilford (Essex, but now part of the London Borough of
Redbridge) still had DC mains in the mid - late 50s, a hangover from the
days of Ilford Tramways when the council decided that if they were going
to provide 600V DC for the trams, they would provide a 200V DC domestic
mains supply. When it was converted to 240V AC I don't know but I'm sure
it wasn't the only place with DC supplies.

I was at school in nearby West Ham during this period and I remember the
extensive street works when the local supply was upgraded from 215V AC
(IIRC) to the standard 240V.

My first 625 line receiver cost me £20 in the late 60s - a brand new Pye
export set in a sealed carton. I modified the sound IF from 5.5MHz
system B to 6MHz system I and added a UHF tuner and probably became one
of the first in the country with a single standard 625 line receiver
when BBC1 & ITV UHF transmissions started at the end of 1970!

It was designed to work on 100/250V AC/DC and had a voltage doubler
arrangement for the lower voltages. The text printed on the rear cover
was in English, French and Arabic!


I remember converting some VHF 405 line set's to 625 UHF but the gain
of the early valve tuners wasn't that good .. when transistor ones came
about .. a remarkable improvement

And yes Cambridge had 200 volts up to the 70's just had to short out a
bit of the mains dropper in most all sets and I could have sworn blind
it was DC too!..

No, it was 200v AC 1959/62 so I doubt if it was altered later.

--
From KT24

Using a RISC OS computer running v5.16

On Fri, 11 Jun 2010 22:22:56 +0000, Laurence Taylor wrote:

Steve Hayes wrote:
On Thu, 10 Jun 2010 21:10:06 +0100, Scott wrote:

Following the North London and clashing signals thread I thought I
would recount an equally weird experience I encountered in my student
days in the 70s. My FM radio used to pick up TV sound. As VHF
television carried AM sound I assumed it must be something to do with
UHF television. I thought about maybe harmonics of the TV signal or a
TV set within the building causing interference.

As I was not studying physics at the time I never got beyond thinking
and never got to the bottom if it. Any ideas?

Scott

I remember this too. It was always ITV and it happened on more than one
FM set in more than one location (including London and also before 625
line UHF started). The TV sound could be heard in the upper part of the
FM band. I've sometimes wondered about it - in particular whether the
transmitters were responsible but didn't need fixing since the unwanted
radiation was on an unused frequency.

I remember this - it was the AM sound signal from the 405 line
transmitter. (On my grotty FM receiver it actually sounded quite good!)

I too was puzzled as to why it happened, and usually on cheaper sets. I
eventually worked out it was due to poor image filtering coupled with a
dirty local oscillator.

I lived in London and the AM sound signal was on 191.25 MHz (say 191 for
convenience), and audible on around 90 MHz.

The arithmetic worked like this:

Local oscillator (90.15+10.7)=100.85
LO 2nd Harmonic 201.7
201.7-191=10.7

I'd have thought it was a problem with the receiver too except:

At the time I remember hearing it in London, I was on a trip over from
Canada and was using a rather cheap and nasty radio. The TV audio was at
something like 101 MHz on the dial with a buzzing, presumably the vision
signal, somewhere above that.

However, the self-same radio never picked up either vision buzzing or FM
sound anywhere I'd used it in Canada or the US (other than channel 6
sound just below 88 MHz which was normal there - that's the frequency
it's on). That's despite the heavy use of various high band VHF (band 3
equivalent) channels across North America.

--
Steve Hayes, South Wales, UK - remove colours from address