Thorn Ultra 1500 restoration - UK Vintage Radio Repair and Restoration Discussion Forum

em536716 · 29th Jun 2018, 4:08 am

The restoration project of the Ultra, with the wonderful Thorn 1500 chassis.

After fixing the simple frame fault, (a quick swap of the frame output valve) I went through and changed capacitors in the line stage

Both stages wouldn’t lock hold so that needed to be looked at.

At this point I cleaned the chassis... to then discover after doing which, I lost video.

I went paranoid and took out every transistor to check for shorts... ended up breaking one of the pins on one... replaced that and reinstalled all of them... still no picture. I then checked the HT feed... (4 HT rails and video transistors runs off HT 3).
Off the smoothing caps I got around 260 volts which seemed to be right, from there it goes through a limiting resistor, which drops the voltage down to 160... OPEN CIRCUIT!

I’ve never worked on a transistor/valve set before so it was a learning experience. I really do like the 1500 chassis, after I examined the diagram and fixed it... it’s quite fun.

I changed the 82K resistor straight away, and had a lovely 160 volt HT (I had to temporarily put 4 resistors in parallel and series to make a higher wattage resistor until the next batch arrives) and plugged my pattern generator in once again... and was greeted with a messy looking image... after some adjustments, (still need to go through the frame stage as there’s slight bending, and adjusting magnets isn’t fixing it!

I also changed a few resistors in the line stage which drifted, but from what I can tell, most of the resistors on the set are fairly good quality so I left them in place.

I also changed every electrolytic capacitor out for modern ones as the ones in place looked very old and dodgy... I took one out which had completely leaked

I know the ultra is quite rare so I’m definitely going to preserve it!

A simple problem caused me to do everything backwards... you live and learn

To add, I also cleaned up the cabinet, and surprisingly, it looks as good as new!

Hybrid tellies · 29th Jun 2018, 9:38 am

Looks very good, what tube is it? I have seen many different model 1500's in my time but have never seen this white Ultra model before.

em536716 · 29th Jun 2018, 3:46 pm

I surprisingly cannot find any documentation of it online.
It looks to be a Gold Star Mazda Tube. Looks to be about 20 inches?

Restoration73 · 29th Jun 2018, 7:21 pm

White was a popular Ultra colour, as used on the 6816 (1590) portable. Your set
may be model 6800, 6807, or 6813. Tube is CME2013R.
Worth upgrading R44, 47k, to 1W rating (30FL2 screen grid)
There is slight underscan, check geometry with a circle pattern or test card.

em536716 · 30th Jun 2018, 5:42 am

Yes you are right. An 6807 I believe. Will change when I next take it down to the workshop if I haven’t already (I didn’t change a few but can’t recall). The magnets on scan coils have become very weak causing the image to twist and distort. I’ve managed to remagnitise them all a little, however I may need to add additional magnets to fit the top and bottom!

Focus Diode · 30th Jun 2018, 7:20 am

Quote:

Originally Posted by Restoration73

There is slight underscan, check geometry with a circle pattern or test card.

Indeed, but this shouldn't be done without keeping an eye on the boost voltage. Set too high can cause the EHT tray to fail.

If the correct voltage still results in lack of width check the scan correction capacitor, the width control and its series resistor.

Brian

mickash · 1st Jul 2018, 1:34 am

Make sure the scan coils are pushed forwards, towards the bowl of the tube and twisted correctly to level the scan.

Michael.

em536716 · 3rd Jul 2018, 6:30 am

Just a few updates on the Ultra.
Has been running perfectly over the past few days. Replaced 82k resistor with appropriate replacement.

I also had to replace the scan coils, as I later found out the original scan coils must’ve had a shorted turn, as the width control would barely fill the screen! There was quite a bit of bowing on the top and sides which I couldn’t adjust out with magnets. Have used the scan coils from a scrap Murphy TV I have, and now all is well!

I’ve attached a picture of the BBC test card you can get off a freeview box (however I wouldn’t use this since it’s meant for widescreen and not accurate)

I think now all I have to do is treat the cracks and chips, and possibly make up some legs for it, and it’ll be done 🙂

em536716 · 3rd Jul 2018, 6:34 am

Quote:

Originally Posted by mickash

Make sure the scan coils are pushed forwards, towards the bowl of the tube and twisted correctly to level the scan.

All seems fine now after the scan coils swap. Can’t believe I missed that, all voltages seem healthy and the set runs fairly cool. The heat mainly came off those scan coils!!

Focus Diode · 3rd Jul 2018, 12:19 pm

I see the linearity sleeve is missing between the CRT neck and scan coils, yet the vertical linearity is close to perfect!

There's a chance the old coils could have overheated if the linearity sleeve was inserted too far in.

Anyway, well done. I once had lack of width on a 1500 caused by the scan coils.

Brian

em536716 · 4th Jul 2018, 5:36 pm

I removed it at first just to test fit it, but decided on not fitting it back. The picture looks as best as it’ll ever be so I’ll nust leave it now.

Does anyone have any legs for this?

jayceebee · 5th Jul 2018, 9:45 pm

Well done for saving another 1500 but I feel you still have issues around the video stages VT8/9. The chassis is an economical and reliable design but it is capable, depending on the CRT of pretty fair results. Have a look at my unfinished Marconi 4821 with it's slightly soft Mullard CRT.

John

29th Jun 2018, 4:08 am	#1
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Thorn Ultra 1500 restoration The restoration project of the Ultra, with the wonderful Thorn 1500 chassis. After fixing the simple frame fault, (a quick swap of the frame output valve) I went through and changed capacitors in the line stage Both stages wouldn’t lock hold so that needed to be looked at. At this point I cleaned the chassis... to then discover after doing which, I lost video. I went paranoid and took out every transistor to check for shorts... ended up breaking one of the pins on one... replaced that and reinstalled all of them... still no picture. I then checked the HT feed... (4 HT rails and video transistors runs off HT 3). Off the smoothing caps I got around 260 volts which seemed to be right, from there it goes through a limiting resistor, which drops the voltage down to 160... OPEN CIRCUIT! I’ve never worked on a transistor/valve set before so it was a learning experience. I really do like the 1500 chassis, after I examined the diagram and fixed it... it’s quite fun. I changed the 82K resistor straight away, and had a lovely 160 volt HT (I had to temporarily put 4 resistors in parallel and series to make a higher wattage resistor until the next batch arrives) and plugged my pattern generator in once again... and was greeted with a messy looking image... after some adjustments, (still need to go through the frame stage as there’s slight bending, and adjusting magnets isn’t fixing it! I also changed a few resistors in the line stage which drifted, but from what I can tell, most of the resistors on the set are fairly good quality so I left them in place. I also changed every electrolytic capacitor out for modern ones as the ones in place looked very old and dodgy... I took one out which had completely leaked I know the ultra is quite rare so I’m definitely going to preserve it! A simple problem caused me to do everything backwards... you live and learn To add, I also cleaned up the cabinet, and surprisingly, it looks as good as new! Attached Thumbnails

29th Jun 2018, 9:38 am	#2
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,967	Re: Thorn ultra 1500 restoration Looks very good, what tube is it? I have seen many different model 1500's in my time but have never seen this white Ultra model before. __________________ Simon BVWS member

29th Jun 2018, 3:46 pm	#3
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Thorn ultra 1500 restoration I surprisingly cannot find any documentation of it online. It looks to be a Gold Star Mazda Tube. Looks to be about 20 inches?

29th Jun 2018, 7:21 pm	#4
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Thorn ultra 1500 restoration White was a popular Ultra colour, as used on the 6816 (1590) portable. Your set may be model 6800, 6807, or 6813. Tube is CME2013R. Worth upgrading R44, 47k, to 1W rating (30FL2 screen grid) There is slight underscan, check geometry with a circle pattern or test card.

30th Jun 2018, 5:42 am	#5
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Thorn ultra 1500 restoration Yes you are right. An 6807 I believe. Will change when I next take it down to the workshop if I haven’t already (I didn’t change a few but can’t recall). The magnets on scan coils have become very weak causing the image to twist and distort. I’ve managed to remagnitise them all a little, however I may need to add additional magnets to fit the top and bottom!

1st Jul 2018, 1:34 am	#7
mickash Hexode Join Date: Sep 2007 Location: Derbyshire, UK. Posts: 289	Re: Thorn ultra 1500 restoration Make sure the scan coils are pushed forwards, towards the bowl of the tube and twisted correctly to level the scan. Michael.

3rd Jul 2018, 6:30 am	#8
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Thorn Ultra 1500 restoration Just a few updates on the Ultra. Has been running perfectly over the past few days. Replaced 82k resistor with appropriate replacement. I also had to replace the scan coils, as I later found out the original scan coils must’ve had a shorted turn, as the width control would barely fill the screen! There was quite a bit of bowing on the top and sides which I couldn’t adjust out with magnets. Have used the scan coils from a scrap Murphy TV I have, and now all is well! I’ve attached a picture of the BBC test card you can get off a freeview box (however I wouldn’t use this since it’s meant for widescreen and not accurate) I think now all I have to do is treat the cracks and chips, and possibly make up some legs for it, and it’ll be done 🙂 Attached Thumbnails

3rd Jul 2018, 12:19 pm	#10
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Thorn Ultra 1500 restoration I see the linearity sleeve is missing between the CRT neck and scan coils, yet the vertical linearity is close to perfect! There's a chance the old coils could have overheated if the linearity sleeve was inserted too far in. Anyway, well done. I once had lack of width on a 1500 caused by the scan coils. Brian

4th Jul 2018, 5:36 pm	#11
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Thorn Ultra 1500 restoration I removed it at first just to test fit it, but decided on not fitting it back. The picture looks as best as it’ll ever be so I’ll nust leave it now. Does anyone have any legs for this?

5th Jul 2018, 9:45 pm	#12
jayceebee Heptode Join Date: Jun 2007 Location: Durham, County Durham, UK. Posts: 640	Re: Thorn Ultra 1500 restoration Well done for saving another 1500 but I feel you still have issues around the video stages VT8/9. The chassis is an economical and reliable design but it is capable, depending on the CRT of pretty fair results. Have a look at my unfinished Marconi 4821 with it's slightly soft Mullard CRT. John