Ekco T311 LOPT - UK Vintage Radio Repair and Restoration Discussion Forum

ppppenguin · 8th Nov 2007, 9:47 am

With thanks to John Wakely (HKshort) I have made a start on my Ekco T311. I visited him the other day and he said that the set would basically be OK so he clipped out the mains filter cap and plugged it in. Most of us would use rather gentler procedures with a variac and/or lamp limiter but John (and Gerry!) are made of sterner stuff and will have none of that sort of thing. After sorting out a dodgy on-off switch the heaters lit up and a minute later up came the line whistle. There were no signs of distress anywhere. We could draw sparks from the EHT rectifier anode but it was AC at the cathode too. We didn't have a spare U25 or known good silicon diode to hand so that's as far as we got before we ran out of time.

The first job is to rebuild the LOPT. It's electrically OK but as is common with these, the plastic casing is in very poor condition. Mine is disintegrating and totally beyond redemption. Not sure what sort of plastic. It looks like it was once clear or amber and doesn't readily melt when touched with a soldering iron. There's no way I can replicate the moulding so it's a case of fabricating something.

I'm plannning to use fibreglass PCB material which is electrically and mechanically up to the job. Not sure about the best way to join the top to the sides. I want as little metal as possible in there so Araldite is a strong possibility. I've also got to work out how to dismantle and refit the anti-corona tags which seem to be riveted together in some way. Other things include how to mount the LOPT itself which will probably be a mixture of glued on bits of fibreglass, nylon bolts and probably a few cable ties. It all sounds like a horrible bodge.

Does anyone have any good ideas?

Al (astral highway) · 8th Nov 2007, 1:06 pm

Quote:

Originally Posted by ppppenguin

Other things include how to mount the LOPT itself ...

Does anyone have any good ideas?

Hi Jeff,

Have you ever come across a product called JB WELD? It's epoxy based, like araldite, but the slow curing version is resistant to extemely high thermal stress, as well as being a way stronger than araldite.

The only downside is its battleship grey appearance, but it is absolutely nails.

It also has a very dialetric coefficient, in my experience.

Good luck

Ed_Dinning · 8th Nov 2007, 8:03 pm

Hi Jeffery, try your local B&Q if large, or a model shop. They often have "metals/ materials bars, rather like the racks that store wooden beading. There is usually a wide variety of plastic rods, squares and angles in handy lengths that will allow you to fabricate what is needed.
Failing that RS has a variety of insulating materials available at a price.

I've seen several of these transformer mouldings and always thought they were perspex, but if the are thermoset it is unlikely. They have probably degenerated due to the ozone.

There is a branch of a national company Brisbay Plastics in our area. They also have a wide variety of plastic materials, manufacture signs and advertising items in plastic. If they have a local branch you may be lucky.

Ed

Sean Williams · 8th Nov 2007, 10:14 pm

Jeffrey,

Paxolin board around 3mm thick will take a thread very well - you can screw the whole assembly together then.

Failing that Superglue works well on GRP - if you visit a model shop they do a slightly thicker glue that has good gap filling properties - this is vital for the porous edges of cut GRP

Cheers
Sean

ppppenguin · 9th Nov 2007, 12:34 am

I'm part way through making a replacement using GRP. I found a length that was just the right width in my box of bits. I've found I'm missing one of the anti-corona contacts so one of the less important contacts will just be a solder tag. I also need to find a way to re-rivet the hollow rivets on these. Assembly will be with a mix of nylon spacers and araldite. The LOPT will be held in position by 4 nylon screws that project through the side cheeks into small recesses in the LOPT itself.

The original plastic is strange stuff. It's all in the bin now but it seemed layered, rather like mica. It disintegrates almost as you look at it.

Mike Phelan · 9th Nov 2007, 8:53 am

Quote:

Originally Posted by ppppenguin

It looks like it was once clear or amber and doesn't readily melt when touched with a soldering iron.

The original plastic is strange stuff. It's all in the bin now but it seemed layered, rather like mica. It disintegrates almost as you look at it.

Jeffrey
It was originally clear, and looked just like Perspex, but when it started to disintegrate it went a yellowish brown and bits flaked off.
We had a T311 at home years ago (the FM version) and the LOPT was fortunately very good, but some we saw in the field had nearly nothing of the plastic left; the U25 was supported on three solder blobs in mid-air!

The later U26 version was quite a bit better. Quite a good reliable set when sorted and de-Hunted.

FERNSEH · 9th Nov 2007, 2:36 pm

Here are two pictures of the Ekco TMB272 line output transformer casing I made last year.
The restoration of two TMB272s appeared last year on the Forum on the 26th June.

DFWB.

ppppenguin · 9th Nov 2007, 3:54 pm

Dave, thanks for the photos. I've just about finished my LOPT rebuild now and should get it back in the set soon. Apart from using GRP mine is a fairly similar design. Neither arrangement is pretty though yours is better than mine because it's transparent. OTOH mine won't suffer from melting while soldering or from the heat while running.

ppppenguin · 9th Nov 2007, 5:10 pm

Here's the rebuilt LOPT with a NOS U25 (actually a Mullard valve, also marked KY50 which is not even listed in TDSL).

I just hope it still works after all that mucking about.

ppppenguin · 9th Nov 2007, 6:41 pm

There was a scare when I thought the overwind was o/c but I think it was just bad soldering on to the the rather mucky bit of wire projecting from the overwind.

Turned on the set and I've got about 7.5kV of EHT which I think is only half what it should be. Nothing seems to be suffering so it's probably not the boost cap or shorted turns on the LOPT. I suppose I ought to check the HT volts and the LOP screen resistor.

Rather than do faultfinding I suppose I should re-cap the set now. Not sure I'll have much time for it over the weekend but I hope I'll be able to write it up as a success story one day.

FERNSEH · 9th Nov 2007, 6:56 pm

Hi Jeffrey,
That's an excellent job, you'll experience no problems with the transformer.
With regards to the Mullard KY80. In the late 60s Mullard marketed valves which were made by Mazda. The valves were assigned with the European type number system. Another example is the Mazda 30PL1 which was given the type number PCL801. You'll notice a curious symbol on the valves which looks like an U. This indicates a third party supplier.

DFWB.

ppppenguin · 9th Nov 2007, 7:08 pm

Quote:

Originally Posted by FERNSEH

With regards to the Mullard KY80.....

On my 2nd photo you can clearly see both the U25 and KY50 markings. The box was a "Kradlepak", marked U25/KY50 and £1.14 P.T. EX. This dates it as post 1971.

ppppenguin · 23rd Feb 2008, 10:58 pm

Success! With some help from John Wakely (heatercathodeshort) my T311 is now giving excellent pictures. The LOPT rebuild was 100% successful and I recapped the timebase chassis last year before it got thrown off the bench. I was down at John's again today. We turned it on and got a raster immediately after warmup. Some kind of picture too. Changed some of the waxed caps on the signal chassis, a bit of very expert tweaking from John and the picture was superb.

The only other work we did was to put the correct value cap in the frame timebase where a wrong value I'd fitted was giving a stretched bottom. John also kindly found me a good used U191 boost diode because he felt the old one was looking a bit past it. The NOS spare I'd brought with me was down to air

The electrolytics are all original and we reckon that they're all OK.

Even the radio worked! Not very well, but the signal down there is poor. May be rather better at my place.

This set is a credit to Ekco. John reckons that Ekco made some of the best sets in the 1950s and he should know, he's probably serviced more sets of that vintage than I've had hot dinners. If my set is anything to go by, I'm inclined to agree with him.

ppppenguin · 24th Feb 2008, 9:41 am

John Wakely's comment on these LOPTs was that the windings were fine but the plastic was rubbish. It's a strange plastic, looks like perspex but thermosetting. It crumbles to dust and delaminates almost like mica. Mine was pretty rough. He's seen these LOPTs working with the plastic totally collapsed and causing fires as a result, all with the set still working.

ppppenguin · 25th Feb 2008, 9:10 am

Does anyone know what this plastic actually was? Looks like perspex but it's a thermoset, totally immune to a hot soldering iron. Clear thermosetting plastics are unusual, the Wikipedia entry doesn't give a lot of information http://en.wikipedia.org/wiki/Thermoset. We are all familiar with urea-formaldehyde and phenolic based plastics such as Bakelite and AFAIK this is never transparent. Polyester resin? Seems a bit unlikely in 1957. Maybe a clear version of Melamine (as used in Formica) but I've never seen that elsewhere.

Heatercathodeshort · 25th Feb 2008, 10:00 am

The Plastic cased transformer introduced in later versions of the model T161/T164 in 1951 and used until 1953/54 in the T205/T217 series never gave the slightest problems. This was the 'Arched Bridge' style. With the introduction of the T221 in 1954 the problems started with the redesigned case. It was never resolved and the problems continued with the last of the true Ekco vertical chassis receivers in 1963. I believe the arched versions were made of Perspex, the clue being the simple 'bent' construction.
I doubt if there is anyone alive that knows the true answer to this but if I'm wrong I suspect they are by now Gar Gar, living in a small bungalow at Southend-on-Sea.
Regards, John.

8th Nov 2007, 9:47 am	#1
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Ekco T311 LOPT With thanks to John Wakely (HKshort) I have made a start on my Ekco T311. I visited him the other day and he said that the set would basically be OK so he clipped out the mains filter cap and plugged it in. Most of us would use rather gentler procedures with a variac and/or lamp limiter but John (and Gerry!) are made of sterner stuff and will have none of that sort of thing. After sorting out a dodgy on-off switch the heaters lit up and a minute later up came the line whistle. There were no signs of distress anywhere. We could draw sparks from the EHT rectifier anode but it was AC at the cathode too. We didn't have a spare U25 or known good silicon diode to hand so that's as far as we got before we ran out of time. The first job is to rebuild the LOPT. It's electrically OK but as is common with these, the plastic casing is in very poor condition. Mine is disintegrating and totally beyond redemption. Not sure what sort of plastic. It looks like it was once clear or amber and doesn't readily melt when touched with a soldering iron. There's no way I can replicate the moulding so it's a case of fabricating something. I'm plannning to use fibreglass PCB material which is electrically and mechanically up to the job. Not sure about the best way to join the top to the sides. I want as little metal as possible in there so Araldite is a strong possibility. I've also got to work out how to dismantle and refit the anti-corona tags which seem to be riveted together in some way. Other things include how to mount the LOPT itself which will probably be a mixture of glued on bits of fibreglass, nylon bolts and probably a few cable ties. It all sounds like a horrible bodge. Does anyone have any good ideas?

8th Nov 2007, 8:03 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Ekco T311 LOPT Hi Jeffery, try your local B&Q if large, or a model shop. They often have "metals/ materials bars, rather like the racks that store wooden beading. There is usually a wide variety of plastic rods, squares and angles in handy lengths that will allow you to fabricate what is needed. Failing that RS has a variety of insulating materials available at a price. I've seen several of these transformer mouldings and always thought they were perspex, but if the are thermoset it is unlikely. They have probably degenerated due to the ozone. There is a branch of a national company Brisbay Plastics in our area. They also have a wide variety of plastic materials, manufacture signs and advertising items in plastic. If they have a local branch you may be lucky. Ed

8th Nov 2007, 10:14 pm	#4
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	Re: Ekco T311 LOPT Jeffrey, Paxolin board around 3mm thick will take a thread very well - you can screw the whole assembly together then. Failing that Superglue works well on GRP - if you visit a model shop they do a slightly thicker glue that has good gap filling properties - this is vital for the porous edges of cut GRP Cheers Sean __________________ Engineers make things work and have spare bits when finished

9th Nov 2007, 12:34 am	#5
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT I'm part way through making a replacement using GRP. I found a length that was just the right width in my box of bits. I've found I'm missing one of the anti-corona contacts so one of the less important contacts will just be a solder tag. I also need to find a way to re-rivet the hollow rivets on these. Assembly will be with a mix of nylon spacers and araldite. The LOPT will be held in position by 4 nylon screws that project through the side cheeks into small recesses in the LOPT itself. The original plastic is strange stuff. It's all in the bin now but it seemed layered, rather like mica. It disintegrates almost as you look at it.

9th Nov 2007, 2:36 pm	#7
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T311 LOPT Here are two pictures of the Ekco TMB272 line output transformer casing I made last year. The restoration of two TMB272s appeared last year on the Forum on the 26th June. DFWB. Attached Thumbnails

9th Nov 2007, 3:54 pm	#8
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT Dave, thanks for the photos. I've just about finished my LOPT rebuild now and should get it back in the set soon. Apart from using GRP mine is a fairly similar design. Neither arrangement is pretty though yours is better than mine because it's transparent. OTOH mine won't suffer from melting while soldering or from the heat while running.

9th Nov 2007, 5:10 pm	#9
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT Here's the rebuilt LOPT with a NOS U25 (actually a Mullard valve, also marked KY50 which is not even listed in TDSL). I just hope it still works after all that mucking about. Attached Thumbnails

9th Nov 2007, 6:41 pm	#10
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT There was a scare when I thought the overwind was o/c but I think it was just bad soldering on to the the rather mucky bit of wire projecting from the overwind. Turned on the set and I've got about 7.5kV of EHT which I think is only half what it should be. Nothing seems to be suffering so it's probably not the boost cap or shorted turns on the LOPT. I suppose I ought to check the HT volts and the LOP screen resistor. Rather than do faultfinding I suppose I should re-cap the set now. Not sure I'll have much time for it over the weekend but I hope I'll be able to write it up as a success story one day.

9th Nov 2007, 6:56 pm	#11
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T311 LOPT Hi Jeffrey, That's an excellent job, you'll experience no problems with the transformer. With regards to the Mullard KY80. In the late 60s Mullard marketed valves which were made by Mazda. The valves were assigned with the European type number system. Another example is the Mazda 30PL1 which was given the type number PCL801. You'll notice a curious symbol on the valves which looks like an U. This indicates a third party supplier. DFWB.

23rd Feb 2008, 10:58 pm	#13
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT Success! With some help from John Wakely (heatercathodeshort) my T311 is now giving excellent pictures. The LOPT rebuild was 100% successful and I recapped the timebase chassis last year before it got thrown off the bench. I was down at John's again today. We turned it on and got a raster immediately after warmup. Some kind of picture too. Changed some of the waxed caps on the signal chassis, a bit of very expert tweaking from John and the picture was superb. The only other work we did was to put the correct value cap in the frame timebase where a wrong value I'd fitted was giving a stretched bottom. John also kindly found me a good used U191 boost diode because he felt the old one was looking a bit past it. The NOS spare I'd brought with me was down to air The electrolytics are all original and we reckon that they're all OK. Even the radio worked! Not very well, but the signal down there is poor. May be rather better at my place. This set is a credit to Ekco. John reckons that Ekco made some of the best sets in the 1950s and he should know, he's probably serviced more sets of that vintage than I've had hot dinners. If my set is anything to go by, I'm inclined to agree with him.

24th Feb 2008, 9:41 am	#14
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT John Wakely's comment on these LOPTs was that the windings were fine but the plastic was rubbish. It's a strange plastic, looks like perspex but thermosetting. It crumbles to dust and delaminates almost like mica. Mine was pretty rough. He's seen these LOPTs working with the plastic totally collapsed and causing fires as a result, all with the set still working.

25th Feb 2008, 9:10 am	#15
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Ekco T311 LOPT Does anyone know what this plastic actually was? Looks like perspex but it's a thermoset, totally immune to a hot soldering iron. Clear thermosetting plastics are unusual, the Wikipedia entry doesn't give a lot of information http://en.wikipedia.org/wiki/Thermoset. We are all familiar with urea-formaldehyde and phenolic based plastics such as Bakelite and AFAIK this is never transparent. Polyester resin? Seems a bit unlikely in 1957. Maybe a clear version of Melamine (as used in Formica) but I've never seen that elsewhere. Last edited by Mike Phelan; 9th Mar 2009 at 4:45 pm. Reason: Removed reference to deleted link.

25th Feb 2008, 10:00 am	#16
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco T311 LOPT The Plastic cased transformer introduced in later versions of the model T161/T164 in 1951 and used until 1953/54 in the T205/T217 series never gave the slightest problems. This was the 'Arched Bridge' style. With the introduction of the T221 in 1954 the problems started with the redesigned case. It was never resolved and the problems continued with the last of the true Ekco vertical chassis receivers in 1963. I believe the arched versions were made of Perspex, the clue being the simple 'bent' construction. I doubt if there is anyone alive that knows the true answer to this but if I'm wrong I suspect they are by now Gar Gar, living in a small bungalow at Southend-on-Sea. Regards, John.