Ekco TMB272 restored - UK Vintage Radio Repair and Restoration Discussion Forum

grindrod · 13th Mar 2006, 12:13 pm

I have been given one of these sets by a friend who has a local TV shop, a customer gave it to him when he delivered a new set!!

It is dusty but there are no signs of any repairs, I have cleared out most of the dust and disconnected the EHT reservoir capacitor ready for a gentle power-up on the Variac. It is date stamped 20th July 1956 on the chassis and tuner.

Are there any known issues/weaknesses with these sets? The circuitry looks fairly standard with an extra bit of switching for the FM radio function.

Does any one have a spare McMurdo connector? I have one configured for AC operation but would like to get hold of one that I can configure for Battery operation.

Cheers, Martin

Heatercathodeshort · 13th Mar 2006, 8:03 pm

Hello,
These sets follow the standard EKCO chassis of that period [1956] but use 6.3volt valves and an elaborate power supply. You will have to replace most of the 'wax' type capacitors and the decoupling capacitors to the screens and cathodes of the i.f. amp valves. Don't do this straight away and get something on the screen first. You may put more faults on the set if you do it all at once. One thing at a time and switch it on to check the results after every replacement. The tube will be ok [Mazda CRM93] I have never seen a bad one. The weak spot is the line output transformer CASE. It is made of plastic and tended to break down on the top between the U25 connections causing burning. It is easily repaired if faulty. The windings will be O.K. A sweet sickly smell will be apparent if it is starting to die. Other than that it will work. First class sets like all Ekco's and gives a super bright picture. Alas the mains connector is very difficult to locate. Running the set on 12volts will flat a car accumulator in a very short time. I believe its about 7 amps. Hope this helps. Regards John.

Danny · 13th Mar 2006, 10:28 pm

Hi these are relible sets if you do the above repaires if you have the mains connector then thats the bonus but if you find a battery conector then i would go strait out and do the lottery because with luck like that you would be a winner! the frame curcuits tend to vary on these sets but shouldnt be to dificult to sort out. oh wilst on the frame if you get cramping then check the little metal diode.
Danny

grindrod · 14th Mar 2006, 9:59 am

Good news everyone! I wound the set up to about 50V on the Variac and left it for the reservoirs to reform, everything looked fine so I wound it up to full supply stopping every 50V for a while.

The line timebase burst into life and a fuzzy horizontal line appeared, obvious fault; no frame timebase.

I disabled the line timebase by removing the G2 feed to the EL81 and went hunting in the frame timebase with the scope.

First observation, the anode of the blocking osc was at 50V even at switch on with a cold valve; leaky decoupling cap. Once replaced the timebase burst into life.

Second observation, the cathode of the O/P stage was at 20V which was double what it should have been, check G1 and find large DC component on it; another leaky cap. Once replaced all the voltages and waveforms looked correct.

Re-enable the line timebase and ta-ra a lovely bright linear raster!

As a precaution I then replaced all the other waxy horrors in both the frame and line timebase.

The screen displays good bright flashes as I rotate the tuner so I will do a DC check on the IF stages and video O/P stage tonight as a precaution.

There is no sound at the moment but that shouldnt be too hard to find.

Hopefully a full report tomorrow

Martin

Heatercathodeshort · 14th Mar 2006, 9:09 pm

Hello! Great news Martin! I told yer so! Ekco made the best televisions of all time. There were other very good makes but Ekco were my favourite. Very easy to get going and the CRM93 was one of the rare Mazda tubes that 'held up'. I think you will find that application of a signal will produce a picture. If it 'cogged' replace the capacitor between the video amp and the sync seperator grid. Keep us informed! Regards John.

grindrod · 15th Mar 2006, 3:37 pm

Just a quick update, did a test with the Domino converter last night that revealed that the gated AGC wasn't working (more waxy horrors I suspect!) so I had an overcontrasty picture and inoperative contrast control.

Sound worked much to my astonishment! There had been no hum or hiss audible, I subsequently found the audio output stage cathode bypass electrolytic missing, just a couple of stubs of lead left!! Hence the low gain.

Timebases are lovely, 9.25kv EHT, linear scans and a nice bright raster!!

I am busy tonight so next installment will be after the weekend.

Cheers all, Martin

grindrod · 23rd Mar 2006, 11:00 am

Hi everyone, latest update!! Having had a weekend away from the workshop (competing in a long distance motorcycle trial on a 1953 James J9!!) I finally got a chance to have another look at the Ekco.

Gated AGC problem was the usual waxy horrors, however, after replacing them I then found the contrast setting highly unstable, a check with the scope revealed no problem with the timing, but wild changes of the video signal. I looked at the signal to the video detector and found large bursts of oscillation. A quick check by removing one of the tuner valves and checking with the scope showed that the first video IF was oscillating. I replaced the 3nF decouplers with 2.2nF HV disc ceramics (didn't have any 3nF!) and hey presto! IF stages all calm.

DC measurements on the video IF stages were all spot on but the voltages around the video output stage showed a low emission valve. Sure enough, after an hour or so the picture started to turn negative as the AGC cranked up the IF gain to compensate for failing video output (the gated AGC senses the back porch black level at the anode of the video output stage).

Oh poo! I don't have any 6F1's in the valve stock!! As a quick fix I swopped the second video IF valve (also a 6F1) with the low emission video output valve. I didn't want to use the first video IF valve as it runs at 15mA anode current and the AGC setting pot is in series with it's anode supply so a low emission valve in this position would upset the AGC alignment.

At last I had a usable video system and the results were quite pleasing, bright stable picture with plenty of contrast with just a hint of sound on vision, the gated AGC works superbly,very important as most of my Sci-Fi B movie collection contains lots of dark scenes!!

I installed the missing cathode decoupler on the ECL80 AF output valve and now have plenty of good quality audio.

All in all a good result, the set works very well, good picture, excellent sync and good sound, and it stays stable over several hours of use. I have ordered a couple of new 6F1's from Colomor to bring the video chain back up to 100%. I will do a full alignment with new valves fitted that will hopefully correct the slight S on V.

Next task is to see if I can get the FM radio working correctly, should be straight forward as it uses the same signal path as the TV with just a change of detector, I will let you know!!

Cheers, Martin

Heatercathodeshort · 23rd Mar 2006, 8:34 pm

Hello again Martin,
Well done with your Ekco! Don't expect too much from the F.M. radio. It will work but selectivity is not too good with todays over congested F.M. band. I had a horror of a fault on A TMB272 last year due to corroded valveholder BASE on the EB91/6AL5 ratio detector valve .........They were crumbling and I was rapidly loosing the will to survive. They are easily replaced from a spare holder saving the need to replace the complete holder. Just a thought if all else fails!
Happy days for me. These sets were only 8 years old when I first worked on them! Regards John.

13th Mar 2006, 12:13 pm	#1
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Ekco TMB272 restored I have been given one of these sets by a friend who has a local TV shop, a customer gave it to him when he delivered a new set!! It is dusty but there are no signs of any repairs, I have cleared out most of the dust and disconnected the EHT reservoir capacitor ready for a gentle power-up on the Variac. It is date stamped 20th July 1956 on the chassis and tuner. Are there any known issues/weaknesses with these sets? The circuitry looks fairly standard with an extra bit of switching for the FM radio function. Does any one have a spare McMurdo connector? I have one configured for AC operation but would like to get hold of one that I can configure for Battery operation. Cheers, Martin

13th Mar 2006, 8:03 pm	#2
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco TMB272 Hello, These sets follow the standard EKCO chassis of that period [1956] but use 6.3volt valves and an elaborate power supply. You will have to replace most of the 'wax' type capacitors and the decoupling capacitors to the screens and cathodes of the i.f. amp valves. Don't do this straight away and get something on the screen first. You may put more faults on the set if you do it all at once. One thing at a time and switch it on to check the results after every replacement. The tube will be ok [Mazda CRM93] I have never seen a bad one. The weak spot is the line output transformer CASE. It is made of plastic and tended to break down on the top between the U25 connections causing burning. It is easily repaired if faulty. The windings will be O.K. A sweet sickly smell will be apparent if it is starting to die. Other than that it will work. First class sets like all Ekco's and gives a super bright picture. Alas the mains connector is very difficult to locate. Running the set on 12volts will flat a car accumulator in a very short time. I believe its about 7 amps. Hope this helps. Regards John.

13th Mar 2006, 10:28 pm	#3
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: Ekco TMB272 Hi these are relible sets if you do the above repaires if you have the mains connector then thats the bonus but if you find a battery conector then i would go strait out and do the lottery because with luck like that you would be a winner! the frame curcuits tend to vary on these sets but shouldnt be to dificult to sort out. oh wilst on the frame if you get cramping then check the little metal diode. Danny

14th Mar 2006, 9:59 am	#4
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Re: Ekco TMB272 Good news everyone! I wound the set up to about 50V on the Variac and left it for the reservoirs to reform, everything looked fine so I wound it up to full supply stopping every 50V for a while. The line timebase burst into life and a fuzzy horizontal line appeared, obvious fault; no frame timebase. I disabled the line timebase by removing the G2 feed to the EL81 and went hunting in the frame timebase with the scope. First observation, the anode of the blocking osc was at 50V even at switch on with a cold valve; leaky decoupling cap. Once replaced the timebase burst into life. Second observation, the cathode of the O/P stage was at 20V which was double what it should have been, check G1 and find large DC component on it; another leaky cap. Once replaced all the voltages and waveforms looked correct. Re-enable the line timebase and ta-ra a lovely bright linear raster! As a precaution I then replaced all the other waxy horrors in both the frame and line timebase. The screen displays good bright flashes as I rotate the tuner so I will do a DC check on the IF stages and video O/P stage tonight as a precaution. There is no sound at the moment but that shouldnt be too hard to find. Hopefully a full report tomorrow Martin

14th Mar 2006, 9:09 pm	#5
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco TMB272 Hello! Great news Martin! I told yer so! Ekco made the best televisions of all time. There were other very good makes but Ekco were my favourite. Very easy to get going and the CRM93 was one of the rare Mazda tubes that 'held up'. I think you will find that application of a signal will produce a picture. If it 'cogged' replace the capacitor between the video amp and the sync seperator grid. Keep us informed! Regards John.

15th Mar 2006, 3:37 pm	#6
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Re: Ekco TMB272 Just a quick update, did a test with the Domino converter last night that revealed that the gated AGC wasn't working (more waxy horrors I suspect!) so I had an overcontrasty picture and inoperative contrast control. Sound worked much to my astonishment! There had been no hum or hiss audible, I subsequently found the audio output stage cathode bypass electrolytic missing, just a couple of stubs of lead left!! Hence the low gain. Timebases are lovely, 9.25kv EHT, linear scans and a nice bright raster!! I am busy tonight so next installment will be after the weekend. Cheers all, Martin

23rd Mar 2006, 11:00 am	#7
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Re: Ekco TMB272 Hi everyone, latest update!! Having had a weekend away from the workshop (competing in a long distance motorcycle trial on a 1953 James J9!!) I finally got a chance to have another look at the Ekco. Gated AGC problem was the usual waxy horrors, however, after replacing them I then found the contrast setting highly unstable, a check with the scope revealed no problem with the timing, but wild changes of the video signal. I looked at the signal to the video detector and found large bursts of oscillation. A quick check by removing one of the tuner valves and checking with the scope showed that the first video IF was oscillating. I replaced the 3nF decouplers with 2.2nF HV disc ceramics (didn't have any 3nF!) and hey presto! IF stages all calm. DC measurements on the video IF stages were all spot on but the voltages around the video output stage showed a low emission valve. Sure enough, after an hour or so the picture started to turn negative as the AGC cranked up the IF gain to compensate for failing video output (the gated AGC senses the back porch black level at the anode of the video output stage). Oh poo! I don't have any 6F1's in the valve stock!! As a quick fix I swopped the second video IF valve (also a 6F1) with the low emission video output valve. I didn't want to use the first video IF valve as it runs at 15mA anode current and the AGC setting pot is in series with it's anode supply so a low emission valve in this position would upset the AGC alignment. At last I had a usable video system and the results were quite pleasing, bright stable picture with plenty of contrast with just a hint of sound on vision, the gated AGC works superbly,very important as most of my Sci-Fi B movie collection contains lots of dark scenes!! I installed the missing cathode decoupler on the ECL80 AF output valve and now have plenty of good quality audio. All in all a good result, the set works very well, good picture, excellent sync and good sound, and it stays stable over several hours of use. I have ordered a couple of new 6F1's from Colomor to bring the video chain back up to 100%. I will do a full alignment with new valves fitted that will hopefully correct the slight S on V. Next task is to see if I can get the FM radio working correctly, should be straight forward as it uses the same signal path as the TV with just a change of detector, I will let you know!! Cheers, Martin

23rd Mar 2006, 8:34 pm	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco TMB272 Hello again Martin, Well done with your Ekco! Don't expect too much from the F.M. radio. It will work but selectivity is not too good with todays over congested F.M. band. I had a horror of a fault on A TMB272 last year due to corroded valveholder BASE on the EB91/6AL5 ratio detector valve .........They were crumbling and I was rapidly loosing the will to survive. They are easily replaced from a spare holder saving the need to replace the complete holder. Just a thought if all else fails! Happy days for me. These sets were only 8 years old when I first worked on them! Regards John.