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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 6th Sep 2022, 6:54 am   #21
Freya
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Default Re: Standards Converter recommissioned.

Hi David,
Would like to see your circuit please to compare chip choice for the interpolator / line store compared to the MK2 dinosaur, think the MK2 was redesigned to use the mach210-20 CPLD which cut down on the chip count to a mere 18!
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Old 8th Sep 2022, 7:40 am   #22
HamishBoxer
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Default Re: Standards Converter recommissioned.

stevehertz, was your modulator made by David Grant I wonder back in the 80's? If so a top class piece of kit, as was the standards converter.
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Old 8th Sep 2022, 10:39 am   #23
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Default Re: Standards Converter recommissioned.

Interpolation, done at analogue levels from the DACs. Been thinking about doing a digital solution but to be honest I just haven't got the time to get around to doing something about it.
History of the converter. The project started in the autumn of 1984; the plan was to have a workable converter ready for the close-down of 405 of transmissions in January 1985.
But wasn't to be so because I developed a serious health issue and it wasn't until the autumn '85 the project was restarted.
The period between 1980 to the early 1990s was the busiest time I've ever experienced in the TV trade.

DFWB.
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Old 8th Sep 2022, 3:13 pm   #24
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Default Re: Standards Converter recommissioned.

How I remember those incredible years! I was placing bulk orders to Toshiba for colour TV and VCRs. Looking through my old stock books I once ordered 24 X 12" mono portables and sold them all in 14 days. Great times never to return.

I built the David Looser modulator David. It still works fine. Your standards converter stood alone in 1984. Absolutely amazing! John.
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Old 8th Sep 2022, 4:32 pm   #25
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Default Re: Standards Converter recommissioned.

Quote:
Originally Posted by FERNSEH View Post

You're welcome to the circuit diagrams of both converters.

DFWB.
I'd be very interested in seeing these circuit diagrams too if you're prepared to make them available
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Old 8th Sep 2022, 9:48 pm   #26
radiomarktv
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Default Re: Standards Converter recommissioned.

Hi David, thank you for sharing your converter with us, a great achievement.
Can you be credited as the first person to produce a home built 405 line standards converter?
I too would like to see the circuit diagrams if ok with you.
Mark.
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Old 9th Sep 2022, 6:52 am   #27
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Default Re: Standards Converter recommissioned.

I too would love to see the circuit diagrams.
PM sent

Peter
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Old 9th Sep 2022, 12:23 pm   #28
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Default Re: Standards Converter recommissioned.

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Originally Posted by radiomarktv View Post
Can you be credited as the first person to produce a home built 405 line standards converter?
As far as I understand apart from the BBC David was the first to produce a working 625 to 405 line converter and led the way for others to follow.
It was an incredible achievement to build something as complex as a standard converter from TTL. Getting it to work at the speeds required for the converter couldn't be easy especially not having a PCB and using vero board.
It had to have taken a huge amount of work and great commitment especially when no one had done it before.
David showed it could be done. Thereby making it easier for anyone after that.

Frank
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Old 9th Sep 2022, 10:28 pm   #29
FERNSEH
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Default Re: Standards Converter recommissioned.

I will be pleased to show to all those interested the circuit diagrams of the two standards converters I constructed in the mid nineteen-eighties.
But I'll need time to redraw the diagrams and descriptions of the workings of the circuits.

DFWB.
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Old 13th Sep 2022, 9:00 pm   #30
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Default Re: Standards Converter recommissioned.

Peter Scott wrote: "I think the set is not doing justice to your converter"

Hi Peter,
A regular client brought his Decca DM45 in for repair. The set has a frame timebase fault.
Using a 625 line Test Card C generator as the signal source for the converter, the 2.5Mc/s definition bars can clearly be seen and the 3meg bars also.
The Marconi VT161 was struggling to resolve the 2.5meg bars. Also, the stability of vertical details is bad.

Let's see what the picture looks like when the Decca is repaired.

DFWB.
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Name:	DM45_FTB_Osc_Fault.jpg
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Old 13th Sep 2022, 10:28 pm   #31
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Default Re: Standards Converter recommissioned.

Quote:
Originally Posted by FERNSEH View Post
Peter Scott wrote: "I think the set is not doing justice to your converter"

Hi Peter,
A regular client brought his Decca DM45 in for repair. The set has a frame timebase fault.
Using a 625 line Test Card C generator as the signal source for the converter, the 2.5Mc/s definition bars can clearly be seen and the 3meg bars also.
The Marconi VT161 was struggling to resolve the 2.5meg bars. Also, the stability of vertical details is bad.

Let's see what the picture looks like when the Decca is repaired.

DFWB.
' Love it!

Go for it David.

Peter
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Old 17th Sep 2022, 10:23 am   #32
FERNSEH
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Default Re: Standards Converter recommissioned.

Attached picture was taken from the screen of the Decca DM45. Showing the 2.5Mc/s definition bars. Camera captures only one picture field.

DFWB.
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Old 17th Sep 2022, 12:09 pm   #33
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Default Re: Standards Converter recommissioned.

Got to get rid of the overshoot on the step response though.

Peter
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Old 17th Sep 2022, 1:09 pm   #34
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Default Re: Standards Converter recommissioned.

Hi Peter,
the video waveforms at the control grid of the video amplifier valve and the grid of the sync separator.
Clearly, the video amplifier needs some attention.

DFWB.
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Name:	DM45_Wfm_Video_Det.jpg
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ID:	264864   Click image for larger version

Name:	DM45_Wfm_Sync_Sep.jpg
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Old 17th Sep 2022, 4:15 pm   #35
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Default Re: Standards Converter recommissioned.

Strangely the first photo (video amp??) looks quite well controlled. Can you probe the video amp anode?

I just looked at the circuit. I see the sync separator grid probably looks much the same as the video amp anode. What happens when you adjust VR10?

Peter

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Old 17th Sep 2022, 8:06 pm   #36
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Default Re: Standards Converter recommissioned.

After replacing C48 in the video amplifier the over-shoot effect has gone.
However, there is a slight loss of definition. The 8.2K anode load resistor has risen to 11K. That component will be replaced.
VR10, the white spot clipper is inactive.

DFWB.
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Name:	DM45_Video_Amp.jpg
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ID:	264884   Click image for larger version

Name:	DM45_Video_PCL84_Anode.jpg
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Old 17th Sep 2022, 9:20 pm   #37
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Default Re: Standards Converter recommissioned.

Excellent! That test card image must be looking much healthier now.

Peter
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Old 17th Sep 2022, 9:21 pm   #38
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Default Re: Standards Converter recommissioned.

Hi
Check C49 for correct value it may have drifted low reducing HF correction.
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Old 20th Sep 2022, 9:53 am   #39
FERNSEH
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Default Re: Standards Converter recommissioned.

The first attachment shows the converted picture on a Bush TV62. That set needs some attention having not been switched on for ages.
The second attachment shows the divider network employed to produce the 405 and 625 timing pulses.

DFWB.
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Name:	Bush_TV62.jpg
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ID:	264996   Click image for larger version

Name:	Standards_Converter_7.jpg
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