Ekco T141 strange fault - UK Vintage Radio Repair and Restoration Discussion Forum

Freya · 15th Nov 2022, 10:04 pm

Anyone seen this behaviour before? set was fully re capped back in 2017 working perfectly every day until recently.

https://1drv.ms/v/s!ApN5zU4cheybpUqS...Er0om?e=L3eMqm

thermionic · 16th Nov 2022, 7:51 am

Hi Stephen.

Line oscillator / Line sync problems, I think I would be swapping valves. Does the T141 have a self oscillating line output stage?

Is it intermittent, or there as soon as the set has warmed up?

Hope you’re well, cheers.

Simon.

Heatercathodeshort · 16th Nov 2022, 12:03 pm

It could be a H/C intermittent short in the CRT. There are also a couple of brown sqaure 100pf silver mica caps in the line oscillator that give trouble, the sort that look like mini dominos. It's an odd fault for an EKCO. Also try a couple of SP41 line osc valves, they can be a bit fussy. John.

Freya · 16th Nov 2022, 3:38 pm

Tried a proper low capacitance heater isolation transformer with no change, the line oscillator remains steady when the problem is displayed. The capacitors on the line oscillator have been changed for silver mica. It gets worse when the backs on and up to temperature.
I am beginning to wonder if the insulated heater winding for the U24 EHT rectifier is breaking down onto another supply within the transformer.

Heatercathodeshort · 17th Nov 2022, 9:19 am

I don't think so. The effect would be very audible if there was a leak. It may be in the video amplifier. J.

Freya · 17th Nov 2022, 5:11 pm

Ok, so swapping the tube over into another set has moved the problem into that set proving John was correct in post #3, although not sure why the independent low capacitance heater transformer did not make any impact though.
Thanks John

thermionic · 17th Nov 2022, 8:00 pm

That’s disappointing and also slightly strange!

I would have expected your experiment with the heater isolation transformer to have made a difference.

I wonder if something strange is going on between grid & cathode? A small bit of crud come adrift somewhere?

If you have a Megger, maybe try a resistance test between grid and cathode & see what you get. (250 Volt range first, maybe)!

Cheers. SimonT.

15th Nov 2022, 10:04 pm	#1
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Ekco T141 strange fault Anyone seen this behaviour before? set was fully re capped back in 2017 working perfectly every day until recently. https://1drv.ms/v/s!ApN5zU4cheybpUqS...Er0om?e=L3eMqm __________________ Stephen _________"It`s only an old telly" ___

16th Nov 2022, 7:51 am	#2
thermionic Heptode Join Date: Apr 2003 Location: Cornwall, UK. Posts: 989	Re: Ekco T141 strange fault Hi Stephen. Line oscillator / Line sync problems, I think I would be swapping valves. Does the T141 have a self oscillating line output stage? Is it intermittent, or there as soon as the set has warmed up? Hope you’re well, cheers. Simon. __________________ The honesty of imperfection..........

16th Nov 2022, 3:38 pm	#4
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: Ekco T141 strange fault Tried a proper low capacitance heater isolation transformer with no change, the line oscillator remains steady when the problem is displayed. The capacitors on the line oscillator have been changed for silver mica. It gets worse when the backs on and up to temperature. I am beginning to wonder if the insulated heater winding for the U24 EHT rectifier is breaking down onto another supply within the transformer. __________________ Stephen _________"It`s only an old telly" ___

17th Nov 2022, 9:19 am	#5
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco T141 strange fault I don't think so. The effect would be very audible if there was a leak. It may be in the video amplifier. J.

17th Nov 2022, 5:11 pm	#6
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: Ekco T141 strange fault Ok, so swapping the tube over into another set has moved the problem into that set proving John was correct in post #3, although not sure why the independent low capacitance heater transformer did not make any impact though. Thanks John __________________ Stephen _________"It`s only an old telly" ___

16th Nov 2022, 12:03 pm	#3
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco T141 strange fault It could be a H/C intermittent short in the CRT. There are also a couple of brown sqaure 100pf silver mica caps in the line oscillator that give trouble, the sort that look like mini dominos. It's an odd fault for an EKCO. Also try a couple of SP41 line osc valves, they can be a bit fussy. John.

17th Nov 2022, 8:00 pm	#7
thermionic Heptode Join Date: Apr 2003 Location: Cornwall, UK. Posts: 989	Re: Ekco T141 strange fault That’s disappointing and also slightly strange! I would have expected your experiment with the heater isolation transformer to have made a difference. I wonder if something strange is going on between grid & cathode? A small bit of crud come adrift somewhere? If you have a Megger, maybe try a resistance test between grid and cathode & see what you get. (250 Volt range first, maybe)! Cheers. SimonT. __________________ The honesty of imperfection..........