Bush TV166u - help needed. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

dryad1313 · 23rd May 2014, 6:57 pm

Thanks for your replies. I'm really hoping it isn't the LOPT for the obvious reasons, so I'll give your suggestion a go, Simon, and report back soon.
Chris

dryad1313 · 23rd May 2014, 8:20 pm

Test over. After 40 minutes running with the anode cap off the LOPT is very warm and the pitch is soft and squishy. The dropper is also really hot. So, I suppose a new LOPT is needed...

jayceebee · 23rd May 2014, 8:43 pm

You might want to look at this thread over on the VRAT forum.

dryad1313 · 23rd May 2014, 10:36 pm

That looks useful - thanks, I might give it a try!

KeithsTV · 24th May 2014, 8:00 am

A work colleague had problems with the LOPT from his TV125 with exactly your symptoms. There is a small vacuum oven at work used for baking BGA devices before fitting them to PCBs. We put the LOPT in his oven at about 50C and full vacuum for a few days then refitted it to the TV which seemed to cure the problem. If you can find someone with one of these ovens it would be worth trying it as it seems to be able to remove any deep seated dampness inside the windings.

Keith

mark pirate · 24th May 2014, 8:43 am

As you really have nothing to lose, I would carefully remove the pitch and bake it in your oven for an hour or so.
This should drive out any residual moisture and may save it.

Mark

Hybrid tellies · 24th May 2014, 4:06 pm

Sorry but not surprised to hear that it the LOPT at fault. Just read the link to the VRAT forum. It certainly is worth a go.

MALC SCOTT · 24th May 2014, 4:52 pm

Last resort you could remove the overwind and fit a tripler.

dryad1313 · 24th May 2014, 5:48 pm

I'll give the suggestion on VRAT a go as I don't know anyone with a vacuum oven. Otherwise it'll have to be Malc's suggestion. Anyone actually done this successfully on this type of LOPT?

molochkartovski · 24th May 2014, 8:41 pm

I had a 640 running on a tripler for a few years when I was teenager in the eighties as I recall it worked far better than the overwind and rectifer valve had ever done

Focus Diode · 24th May 2014, 10:47 pm

I adapted one of these sets to work with a Thorn 1500 doubler. It lasted about six months before the primary failed unfortunately.

Brian

MALC SCOTT · 25th May 2014, 12:17 am

The EHT regulation with the tripler is never as good as with the valve.

Focus Diode · 28th May 2014, 8:52 am

It wouldn't be impossible to adapt one of these sets to work with a Thorn Jellypot LOPT, as most of us know an earlier TV125 was successfully modified by Keith Hamer & Gary Smith (September 1982 issue of "Television" I think it was). For the A640 series an additional mains transformer will be needed as I remember the LT supplies were provided via a winding on the LOPT which explains why a failed primary gives the impression of a "Dead set".

Certainly in the thread subject the primary is working OK, my example was unfortunately short lived on fitting the doubler yet Molochkartovsky got a few years from his example.

Cheers,
Brian

Heatercathodeshort · 28th May 2014, 9:29 am

If you can find another transformer such as the Plessey version of the Thorn 850 and many others, you could fit the overwind. The 640 transformer is easily dismantled but if you go down this path make sure you don't lose the little paper gapping disks between the ferrite cores. They are usually safely stuck but can flutter out unnoticed causing saturation problems on reassembly. Just a thought. John.

23rd May 2014, 6:57 pm	#21
dryad1313 Tetrode Join Date: Sep 2012 Location: South Norfolk, UK. Posts: 72	Re: Bush TV166u - help needed. Thanks for your replies. I'm really hoping it isn't the LOPT for the obvious reasons, so I'll give your suggestion a go, Simon, and report back soon. Chris

23rd May 2014, 8:20 pm	#22
dryad1313 Tetrode Join Date: Sep 2012 Location: South Norfolk, UK. Posts: 72	Re: Bush TV166u - help needed. Test over. After 40 minutes running with the anode cap off the LOPT is very warm and the pitch is soft and squishy. The dropper is also really hot. So, I suppose a new LOPT is needed...

23rd May 2014, 8:43 pm	#23
jayceebee Heptode Join Date: Jun 2007 Location: Durham, County Durham, UK. Posts: 640	Re: Bush TV166u - help needed. You might want to look at this thread over on the VRAT forum.

23rd May 2014, 10:36 pm	#24
dryad1313 Tetrode Join Date: Sep 2012 Location: South Norfolk, UK. Posts: 72	Re: Bush TV166u - help needed. That looks useful - thanks, I might give it a try!

24th May 2014, 8:00 am	#25
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,573	Re: Bush TV166u - help needed. A work colleague had problems with the LOPT from his TV125 with exactly your symptoms. There is a small vacuum oven at work used for baking BGA devices before fitting them to PCBs. We put the LOPT in his oven at about 50C and full vacuum for a few days then refitted it to the TV which seemed to cure the problem. If you can find someone with one of these ovens it would be worth trying it as it seems to be able to remove any deep seated dampness inside the windings. Keith

24th May 2014, 8:43 am	#26
mark pirate Dekatron Join Date: Mar 2008 Location: Worthing, West Sussex, UK Posts: 5,185	Re: Bush TV166u - help needed. As you really have nothing to lose, I would carefully remove the pitch and bake it in your oven for an hour or so. This should drive out any residual moisture and may save it. Mark

24th May 2014, 4:06 pm	#27
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: Bush TV166u - help needed. Sorry but not surprised to hear that it the LOPT at fault. Just read the link to the VRAT forum. It certainly is worth a go. __________________ Simon BVWS member

24th May 2014, 4:52 pm	#28
MALC SCOTT Octode Join Date: Aug 2006 Location: Willington, County Durham, UK. Posts: 1,499	Re: Bush TV166u - help needed. Last resort you could remove the overwind and fit a tripler. __________________ Malc Scott

24th May 2014, 5:48 pm	#29
dryad1313 Tetrode Join Date: Sep 2012 Location: South Norfolk, UK. Posts: 72	Re: Bush TV166u - help needed. I'll give the suggestion on VRAT a go as I don't know anyone with a vacuum oven. Otherwise it'll have to be Malc's suggestion. Anyone actually done this successfully on this type of LOPT?

24th May 2014, 8:41 pm	#30
molochkartovski Tetrode Join Date: Jun 2005 Location: Wilton, Salisbury, Wiltshire, UK. Posts: 66	Re: Bush TV166u - help needed. I had a 640 running on a tripler for a few years when I was teenager in the eighties as I recall it worked far better than the overwind and rectifer valve had ever done

24th May 2014, 10:47 pm	#31
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Bush TV166u - help needed. I adapted one of these sets to work with a Thorn 1500 doubler. It lasted about six months before the primary failed unfortunately. Brian

25th May 2014, 12:17 am	#32
MALC SCOTT Octode Join Date: Aug 2006 Location: Willington, County Durham, UK. Posts: 1,499	Re: Bush TV166u - help needed. The EHT regulation with the tripler is never as good as with the valve. __________________ Malc Scott

28th May 2014, 8:52 am	#33
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Bush TV166u - help needed. It wouldn't be impossible to adapt one of these sets to work with a Thorn Jellypot LOPT, as most of us know an earlier TV125 was successfully modified by Keith Hamer & Gary Smith (September 1982 issue of "Television" I think it was). For the A640 series an additional mains transformer will be needed as I remember the LT supplies were provided via a winding on the LOPT which explains why a failed primary gives the impression of a "Dead set". Certainly in the thread subject the primary is working OK, my example was unfortunately short lived on fitting the doubler yet Molochkartovsky got a few years from his example. Cheers, Brian

28th May 2014, 9:29 am	#34
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Bush TV166u - help needed. If you can find another transformer such as the Plessey version of the Thorn 850 and many others, you could fit the overwind. The 640 transformer is easily dismantled but if you go down this path make sure you don't lose the little paper gapping disks between the ferrite cores. They are usually safely stuck but can flutter out unnoticed causing saturation problems on reassembly. Just a thought. John.