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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions. |
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15th Mar 2015, 5:42 pm | #41 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: An ITV converter.
The problem of patterning on Band 3 renders the converter unusable. Even with the Band 1 signal attenuated the patterning is still present. So what can be done about it? For starters we know that the problem is not caused by direct injection of the Band 1 signal from a transmitter and the reason for the B1 breakthough on a Band 3 channel is the result of leakage inside the converter.
Pull out the Band 1 input and the patterning disappears. Examining the circuit diagram reveals that on Band three channels the Band I input is terminated by a 68 ohm resistor and the link between the Band 1 input to the output socket is broken. Shorting out the 68ohm termination resistor solves the problem, no breakthough whatsoever. In fact EMI did this in their converter. The Band 1 aerial was simply shorted out. In practise that was OK but nowadays we often connect more than one 405 line receiver to our aerial systems and the Band 1 signal supplying other sets will be degraded when the converter is switched to Band 3. Actually, I'd imagine in the old days viewers simply pulled out the Band 1 aerial plug when they watched ITV. That action would get rid of the patterning. Something to discuss perhaps? DFWB. |
15th Mar 2015, 8:46 pm | #42 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: An ITV converter.
Follow up to my last post. R13 the Band 1 termination resistor has been shorted out and the patterning problem on Band 3 has been solved.
DFWB. |
3rd Jan 2016, 3:23 pm | #43 |
Heptode
Join Date: Sep 2009
Location: Kinver, Staffordshire, UK.
Posts: 634
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Re: An ITV converter.
I acquired this band 3 converter recently so after cleaning it up I thought I would post a picture because I`v never seen one this colour before.
There also should be two smaller knobs on the metal shafts but these were missing off the unit when I got it , I`ll never find 2 knobs that colour but its a converter worth keeping. Its made by Wolsey. Robin |
12th Jan 2016, 10:49 pm | #44 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: An ITV converter.
Hi Robin,
Is it a switch tuner like the Invicta 245 converter which started this thread? Or is the tuner continuously variable. What type of valves are employed in the converter? DFWB. |
13th Jan 2016, 12:34 am | #45 |
Heptode
Join Date: Sep 2009
Location: Kinver, Staffordshire, UK.
Posts: 634
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Re: An ITV converter.
Hi David
This is a switched tuner with a fine tuning control. The valves are 30C1 and 30L1. Robin |
5th Feb 2016, 1:02 am | #46 |
Heptode
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
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Re: An ITV converter.
Hi all,
Does anyone know who made this converter? It has no maker's markings and has a Spencer-West kind of look to it. The valves are both type 6BW7. The front panel looks like paxolin, but is actually brown painted steel. The casing is light straw painted tin plate with louvers at the sides. I tested it and found the transformer prone to primary-to-chassis breakdown I tried it connected to an isolation transformer and it worked. I've taken the plug fuse out now though. It is hardly worth re-winding the transformer... Cheers Andy
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5th Feb 2016, 12:37 pm | #47 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: An ITV converter.
Hi Andy,
I'm sure a similar looking band 3 converter was advertised in the Practical Television magazine offered fully built or as a kit. Used two EF80s instead of the 6BW7. You'd think they'd use a better pair of valves though. 100Mhz was considered the limit for those RF pentodes. EF95/6AK5 is good for 400Mhz. DFWB. |