Ultra V71 / W72 1951? - UK Vintage Radio Repair and Restoration Discussion Forum

boiss · 7th Aug 2025, 4:55 pm

I'm still with this set after nearly a year, basically returned parts of the set to their original state and finally I have EHT and a faint screen now but I was wondering how much the tube might have gone downhill. I remember a friend of mine used to zap the Cathode to grid with a cap charged to about 250V to sort of strip off some of the poisoned surface of the cathode. It seemed to work very well. The mods that had been done to this set and the bodge job done by someone with no electronics kbnowledge meant that the tube had been running with no HT and the grid 100V positive in relation to the grid. Now the Grid is slightly negative wrt the cathode and a very dim rectangle can be seen in a slightly darkened room.
I might try zapping the tube, has anyone done this?
M

boiss · 7th Aug 2025, 9:18 pm

In a darkened room the Frame is visible and responds to the H & V Frequencies and Amplitudes. It s inot very bright. The brightness control varies the brightness very little and cuts off with V GC at -30V, About right for this Tube CRM121, Going positive Brightness increases up to about 0V after this there is no difference up to +100V. The frame doesn't bloom with any adjustments in width, height or brightness. I think the tube is Knackered !
By the way the magnetic focusing is pretty useless too, although depending on Vertical F settings, flyback lines can be seen.
M

music-centre · 8th Aug 2025, 3:52 pm

https://www.vintage-radio.net/forum/showthread.php?t=40552

If you are certain the tube is definitely useless I have used the simple type of "rejuvenator" in the PDF in this post with good results many years ago but only lasting for a certain time and only as a last resort of course.

boiss · 9th Aug 2025, 10:36 pm

I remember my friend having a setup like this back in 75, I was never that interested as I had a Philips service centre and the TVs I saw were K9, K11, and the multistandard sets Both the new transistorised ones and the awful valve jobbies with the dodgy relays. I did see some older valve sets but most people used their local repair man.
Good to see this I remember him with his lightbulbs and the sparking inside the tube Cathode grid Area. I will talk to the owner and give it a try.
Thanks a bunch.
M

Incidentally I have been told that it was about 4 years ago that they had seen a picture on thge screen before it went pop and they got the soldering iron out! I don't think they seriously want to watch programs, it would just be to show that the set worked.

boiss · 24th Sep 2025, 3:23 pm

The good news and the bad news.
Sorted out the Circuit and found an oddity too the booster circuit was completely different being from the YA72/73 series which really had me going as the bodgers had fitted different resistors aliong with a 2.7K which didn't fit in with any circuit. Anyway lots of Line O/P now. Because the Tube seemed almost dead the owner brought me over a tube regenerator that had been built from a 1975 Practical TV design. Unfortunately it didn't have a 2V heater option. I dug out an old toroid and wound on some turns 16 gave me 2V, Added another 8 turns with different colour wire, 3V and another colour 8 turns, 4V.
I ran the regenerator etc on 2V, no change, Changed to 3V and tried again. Returning to 2V the raster was just visible in daylight. As instructed back to the Regen just touching the 4V for second caused a flash. Back to the 2V, Heater very bright, Screen blank! Whoops.................So the filament has partially gone S/C. Anyway I took pics of everything and the owner says he has a regunned CRM121 which he will bring me next month. Enough of his regenerator. We have agreed to Fit the new tube together!!!!
M

7th Aug 2025, 4:55 pm	#1
boiss Hexode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 258	Ultra V71 / W72 1951? I'm still with this set after nearly a year, basically returned parts of the set to their original state and finally I have EHT and a faint screen now but I was wondering how much the tube might have gone downhill. I remember a friend of mine used to zap the Cathode to grid with a cap charged to about 250V to sort of strip off some of the poisoned surface of the cathode. It seemed to work very well. The mods that had been done to this set and the bodge job done by someone with no electronics kbnowledge meant that the tube had been running with no HT and the grid 100V positive in relation to the grid. Now the Grid is slightly negative wrt the cathode and a very dim rectangle can be seen in a slightly darkened room. I might try zapping the tube, has anyone done this? M

7th Aug 2025, 9:18 pm	#2
boiss Hexode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 258	Re: Ultra V71 / W72 1951? In a darkened room the Frame is visible and responds to the H & V Frequencies and Amplitudes. It s inot very bright. The brightness control varies the brightness very little and cuts off with V GC at -30V, About right for this Tube CRM121, Going positive Brightness increases up to about 0V after this there is no difference up to +100V. The frame doesn't bloom with any adjustments in width, height or brightness. I think the tube is Knackered ! By the way the magnetic focusing is pretty useless too, although depending on Vertical F settings, flyback lines can be seen. M Last edited by boiss; 7th Aug 2025 at 9:25 pm.

8th Aug 2025, 3:52 pm	#3
music-centre Heptode Join Date: Sep 2007 Location: Brentwood, Essex, UK. Posts: 813	Re: Ultra V71 / W72 1951? https://www.vintage-radio.net/forum/showthread.php?t=40552 If you are certain the tube is definitely useless I have used the simple type of "rejuvenator" in the PDF in this post with good results many years ago but only lasting for a certain time and only as a last resort of course.

9th Aug 2025, 10:36 pm	#4
boiss Hexode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 258	Re: Ultra V71 / W72 1951? I remember my friend having a setup like this back in 75, I was never that interested as I had a Philips service centre and the TVs I saw were K9, K11, and the multistandard sets Both the new transistorised ones and the awful valve jobbies with the dodgy relays. I did see some older valve sets but most people used their local repair man. Good to see this I remember him with his lightbulbs and the sparking inside the tube Cathode grid Area. I will talk to the owner and give it a try. Thanks a bunch. M Incidentally I have been told that it was about 4 years ago that they had seen a picture on thge screen before it went pop and they got the soldering iron out! I don't think they seriously want to watch programs, it would just be to show that the set worked. Last edited by boiss; 9th Aug 2025 at 10:45 pm.

24th Sep 2025, 3:23 pm	#5
boiss Hexode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 258	Re: Ultra V71 / W72 1951? The good news and the bad news. Sorted out the Circuit and found an oddity too the booster circuit was completely different being from the YA72/73 series which really had me going as the bodgers had fitted different resistors aliong with a 2.7K which didn't fit in with any circuit. Anyway lots of Line O/P now. Because the Tube seemed almost dead the owner brought me over a tube regenerator that had been built from a 1975 Practical TV design. Unfortunately it didn't have a 2V heater option. I dug out an old toroid and wound on some turns 16 gave me 2V, Added another 8 turns with different colour wire, 3V and another colour 8 turns, 4V. I ran the regenerator etc on 2V, no change, Changed to 3V and tried again. Returning to 2V the raster was just visible in daylight. As instructed back to the Regen just touching the 4V for second caused a flash. Back to the 2V, Heater very bright, Screen blank! Whoops.................So the filament has partially gone S/C. Anyway I took pics of everything and the owner says he has a regunned CRM121 which he will bring me next month. Enough of his regenerator. We have agreed to Fit the new tube together!!!! M