Flyback blanking on TV22? - UK Vintage Radio Repair and Restoration Discussion Forum

Boom · 21st May 2013, 6:37 pm

Has anyone tried this modification to enable flyback blanking on a TV22?

The following article seems to say that the tube drive is the 'right way around'
for the mod' and that only a cap' and a resistor are needed but I'm a bit confused as to where I'd take the vertical pulse from.

Any ideas?

http://www.earlytelevision.org/vertical_blaniking.html

IJK2008 · 21st May 2013, 7:12 pm

Hello Boom

I did a similar mod on my American Motorola set - it was explained on a posting on the US "antiqueradio" forum. Hadn't thought to try it on anything else.

Cheers

Ian

Heatercathodeshort · 21st May 2013, 7:16 pm

The capacitor seems a little high to me. I would suggest .0047 for a start connected to the frame output anode. J.

Boom · 21st May 2013, 7:21 pm

Thanks Ian. The problem I have is that in the modification circuit the pulse is taken off from a center trapped transformer but in the TV22 circuit the anode load from the frame output is one winding with no tap.

I've tried connecting the r/c network to either side of the frame coils but neither way around gives a watchable picture.

The other end of the r/c is going to the crt cathode. I'm not convinced this mod' can be done with a TV22.

Boom · 21st May 2013, 7:21 pm

Quote:

Originally Posted by Heatercathodeshort

The capacitor seems a little high to me. I would suggest .0047 for a start connected to the frame output anode. J.

That's what I thought. I'll knock it back a bit and try.

Boom · 22nd May 2013, 3:12 pm

Right, using a 100k resistor with a .005 cap' in series I connected the resistor to the tube base (kathode) and the cap' to the ECL80 FTB anode the flyback lines totally vanish.

The problem is that the video output is swamped and the line sync is knocked flying giving squiggles/unlocked line over the top half of the picture.

I haven't got around to trying anything else yet but I don't feel that it is radiation from the video lead or FTB doing this. I suspect it is loading the video output stage that is causing the problem.

What to do about it?

21st May 2013, 6:37 pm	#1
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Flyback blanking on TV22? Has anyone tried this modification to enable flyback blanking on a TV22? The following article seems to say that the tube drive is the 'right way around' for the mod' and that only a cap' and a resistor are needed but I'm a bit confused as to where I'd take the vertical pulse from. Any ideas? http://www.earlytelevision.org/vertical_blaniking.html

21st May 2013, 7:12 pm	#2
IJK2008 Hexode Join Date: Feb 2008 Location: Glasgow, UK. Posts: 321	Re: Flyback blanking on TV22? Hello Boom I did a similar mod on my American Motorola set - it was explained on a posting on the US "antiqueradio" forum. Hadn't thought to try it on anything else. Cheers Ian

21st May 2013, 7:16 pm	#3
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Flyback blanking on TV22? The capacitor seems a little high to me. I would suggest .0047 for a start connected to the frame output anode. J.

21st May 2013, 7:21 pm	#4
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Re: Flyback blanking on TV22? Thanks Ian. The problem I have is that in the modification circuit the pulse is taken off from a center trapped transformer but in the TV22 circuit the anode load from the frame output is one winding with no tap. I've tried connecting the r/c network to either side of the frame coils but neither way around gives a watchable picture. The other end of the r/c is going to the crt cathode. I'm not convinced this mod' can be done with a TV22.

22nd May 2013, 3:12 pm	#6
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Re: Flyback blanking on TV22? Right, using a 100k resistor with a .005 cap' in series I connected the resistor to the tube base (kathode) and the cap' to the ECL80 FTB anode the flyback lines totally vanish. The problem is that the video output is swamped and the line sync is knocked flying giving squiggles/unlocked line over the top half of the picture. I haven't got around to trying anything else yet but I don't feel that it is radiation from the video lead or FTB doing this. I suspect it is loading the video output stage that is causing the problem. What to do about it?