Ekco T221. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 19th Jul 2016, 11:13 pm

11:13pm:
Returned to the workshop late this evening, I had to go there anyway to dump some stuff in the Biffa bin.
Have disconnected the scan coil leads from the frame output transformer. Sure enough it's safe to say that insulation between the line and frame coils has broken down. Now there is a healthy spark at the U25 anode terminal. That valve is not connected up yet because I've got doubts about the visconol EHT capacitor.

DFWB.

FERNSEH · 20th Jul 2016, 10:09 am

From the 1955/56 R & T servicing book. The circuit diagram of the timebases.
Note position of the line linearity and width controls, between the two sections of the scan coils.

DFWB.

FERNSEH · 23rd Jul 2016, 5:22 pm

Collected the scan coils from Mike's (Mikeymushradio) on Thursday evening. Instead of removing the scan coils from a TMB272 the scan coil assembly was removed from the chassis of an Ekco T327. The later model coils are essentially the same as those in the T221 except the line coils are connected directly in series instead of the arrangement in the T221 in which the linearity and width coils are connected between the pair of line deflector coils.
All that is required to use the replacement scan coils in the T221 is to disconnect one of the line coils from the common connection tag and add another anchor tag for the disconnected lead out wire. This has now been done so now it's the scary part of the job in which the CRT has to come out. Removal and refitting the CRT in the Ekco T221 and T231 was discussed in the Practical Television magazine.
Like many other round Mazda CRTs the glass is very thin, much thinner than the rectangular 14" CRTs made by Mullard and many other firms. It wasn't until 1956 when Mazda introduced a rectangular faceplate CRT, strange because the company along with rival Mullard offered a rectangular 17" CRT in 1953.
The metal CRT securing bands around the periphery of the faceplate are stuck fast and considerable care will have to be exercised to remove them, I've squirted WD40 on the rubber strips between the glass bowl and the metal clamp bands, just leave the fluid to it's job and soften the rubber, daren't use force on fragile CRTs.

DFWB.

FERNSEH · 25th Jul 2016, 10:07 pm

All that effort has proven worthwhile. The replacement scan coils are perfect, just one adjustment to do, the picture is upside down. Plenty spare height and width and the linearity is good.
The Mazda CRM141 displays a really bright picture. Because of that displaced CRT mounting bracket it was a bit of a fight to remove the CRT assembly. However, refitting the CRT into the cabinet was easy because those brackets are now correctly recessed into the cabinet sides.
The set was still in use in 1963. The RF amplifier valve was replaced that year with a Mullard PCC84 which has the date code B3D2, April 1963. It's likely the other tuner valve was also replaced in the sixties, it's a 30C1 (PCF80). After the formation of Thorn-AEI valves and tubes later Mazda valves had a Brimar look about them.

It's desirable but not essential that the EHT smoothing capacitor is present in the circuit. I'm considering restuffing the TCC Visconol capacitor. The capacitor serves as a support for the EHT metrosil, a device to maintain a steady load across the EHT supply.
The attachment shows the CRT assembly of the Ekco T231 the 17" version of the T221.

DFWB.

FERNSEH · 27th Jul 2016, 9:53 am

I've finally worked out the wiring to the scanning coils. Although electrically identical the connections of the replacement scan coil assembly are totally different, hence the upside down picture. After that fault was sorted out the letter "C" on the test card was found to be the wrong way around. Because of the split coils arrangement in the T221 the connections of both line deflector coils had to be reversed.
The scanning coils fitted in very early production models were known to fail. Later coils sets have improved insulation between the line and frame coils. This can be seen in the replacement scan coils.
Other faults found: Frame hold was weak, now sorted. The interlace diode and frame pulse integrating capacitor needed replacement, frame lock is now firm. Excellent interlace, no line pairing.

Sound is a bit better but still could do with bit more volume. IF transformers peak up OK, the fault might well be in the AF stages. The output from the detector drives the 10P13 direct.

The CRT is very good, it's not often one sees a CRM141 so good.

DFWB.

unitaudio · 27th Jul 2016, 12:19 pm

This is beginning to sound very promising. Good to hear the tube's a good 'un.

Regards,
Paul

FERNSEH · 27th Jul 2016, 1:36 pm

I wish I could show pictures but for some reason my cameras will not work on Windows 10. In fact I bought another camera a week ago and that doesn't work either.
However, the set's owner might come around on Saturday to collect the set and he will I'm sure take some off screen pictures for us.

DFWB.

FERNSEH · 30th Jul 2016, 4:42 pm

Today, the owner of the Ekco T221 was hoping to collect the repaired set but unfortunately it wasn't to be so, the replacement scan coils have failed again.
Same fault as before, a low resistance reading between the line and frame coils.
It is now apparent what is causing the problem, the height compensation thermistor in series with the frame coils is positioned tight close to the left side line coil, not a good idea considering the high peak voltages present in the line coils.
Otherwise apart from that design flaw, the line and frame coils are well insulated from each other by means of plastic spacers and cellophane.
The only answer to the problem is to reposition the thermistor or remove it from the FTB circuit altogether and see what happens.

DFWB.

Heatercathodeshort · 30th Jul 2016, 6:58 pm

Your very unlucky with those coils David. I knew about the weakness with the early ones but by the time I entered the trade in the very early 60's the faulty ones had all been replaced. I have the T283 coils if you need them. John.

Heatercathodeshort · 1st Aug 2016, 8:14 am

All is not lost David,
I bit the bullet on Sunday and dragged this T283 out of loft 2. [Easier said than done but I did find some interesting items I had forgotten about..] It was minus a back and the side escutcheon. It was never going to be restored and will be a good donor to a wide range of Ekco models.
I have retained all the useful bits from the chassis including the tube cradle and Mazda ReLife CRM141 CRT and dumped the rest including the cabinet. Life is too short.
The scan coils and mains dropper are on their way to you this morning and I hope you have more success with these. Regards, John.

FERNSEH · 5th Aug 2016, 4:41 pm

Hi John,
The T283 scanning coils have done the trick, the T221 is working again. In the T283 pin 4 of the coils' octal plug is connected to the boost rail and in the T221 the lead goes to the chassis. It was just a simple matter of swapping the wires around.
The picture quality of these sets is suburb, just as I remember almost sixty years ago a similar set on those holiday visits to Hove.

DFWB.

19th Jul 2016, 11:13 pm	#21
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. 11:13pm: Returned to the workshop late this evening, I had to go there anyway to dump some stuff in the Biffa bin. Have disconnected the scan coil leads from the frame output transformer. Sure enough it's safe to say that insulation between the line and frame coils has broken down. Now there is a healthy spark at the U25 anode terminal. That valve is not connected up yet because I've got doubts about the visconol EHT capacitor. DFWB.

20th Jul 2016, 10:09 am	#22
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. From the 1955/56 R & T servicing book. The circuit diagram of the timebases. Note position of the line linearity and width controls, between the two sections of the scan coils. DFWB. Attached Thumbnails

23rd Jul 2016, 5:22 pm	#23
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. Collected the scan coils from Mike's (Mikeymushradio) on Thursday evening. Instead of removing the scan coils from a TMB272 the scan coil assembly was removed from the chassis of an Ekco T327. The later model coils are essentially the same as those in the T221 except the line coils are connected directly in series instead of the arrangement in the T221 in which the linearity and width coils are connected between the pair of line deflector coils. All that is required to use the replacement scan coils in the T221 is to disconnect one of the line coils from the common connection tag and add another anchor tag for the disconnected lead out wire. This has now been done so now it's the scary part of the job in which the CRT has to come out. Removal and refitting the CRT in the Ekco T221 and T231 was discussed in the Practical Television magazine. Like many other round Mazda CRTs the glass is very thin, much thinner than the rectangular 14" CRTs made by Mullard and many other firms. It wasn't until 1956 when Mazda introduced a rectangular faceplate CRT, strange because the company along with rival Mullard offered a rectangular 17" CRT in 1953. The metal CRT securing bands around the periphery of the faceplate are stuck fast and considerable care will have to be exercised to remove them, I've squirted WD40 on the rubber strips between the glass bowl and the metal clamp bands, just leave the fluid to it's job and soften the rubber, daren't use force on fragile CRTs. DFWB.

25th Jul 2016, 10:07 pm	#24
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. All that effort has proven worthwhile. The replacement scan coils are perfect, just one adjustment to do, the picture is upside down. Plenty spare height and width and the linearity is good. The Mazda CRM141 displays a really bright picture. Because of that displaced CRT mounting bracket it was a bit of a fight to remove the CRT assembly. However, refitting the CRT into the cabinet was easy because those brackets are now correctly recessed into the cabinet sides. The set was still in use in 1963. The RF amplifier valve was replaced that year with a Mullard PCC84 which has the date code B3D2, April 1963. It's likely the other tuner valve was also replaced in the sixties, it's a 30C1 (PCF80). After the formation of Thorn-AEI valves and tubes later Mazda valves had a Brimar look about them. It's desirable but not essential that the EHT smoothing capacitor is present in the circuit. I'm considering restuffing the TCC Visconol capacitor. The capacitor serves as a support for the EHT metrosil, a device to maintain a steady load across the EHT supply. The attachment shows the CRT assembly of the Ekco T231 the 17" version of the T221. DFWB. Attached Thumbnails

27th Jul 2016, 9:53 am	#25
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. I've finally worked out the wiring to the scanning coils. Although electrically identical the connections of the replacement scan coil assembly are totally different, hence the upside down picture. After that fault was sorted out the letter "C" on the test card was found to be the wrong way around. Because of the split coils arrangement in the T221 the connections of both line deflector coils had to be reversed. The scanning coils fitted in very early production models were known to fail. Later coils sets have improved insulation between the line and frame coils. This can be seen in the replacement scan coils. Other faults found: Frame hold was weak, now sorted. The interlace diode and frame pulse integrating capacitor needed replacement, frame lock is now firm. Excellent interlace, no line pairing. Sound is a bit better but still could do with bit more volume. IF transformers peak up OK, the fault might well be in the AF stages. The output from the detector drives the 10P13 direct. The CRT is very good, it's not often one sees a CRM141 so good. DFWB.

27th Jul 2016, 12:19 pm	#26
unitaudio Heptode Join Date: Sep 2013 Location: Manchester, UK. Posts: 862	Re: Ekco T221. This is beginning to sound very promising. Good to hear the tube's a good 'un. Regards, Paul __________________ ...No, it's not supposed to pick up the World Service, it's not a radio!

27th Jul 2016, 1:36 pm	#27
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. I wish I could show pictures but for some reason my cameras will not work on Windows 10. In fact I bought another camera a week ago and that doesn't work either. However, the set's owner might come around on Saturday to collect the set and he will I'm sure take some off screen pictures for us. DFWB.

30th Jul 2016, 4:42 pm	#28
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. Today, the owner of the Ekco T221 was hoping to collect the repaired set but unfortunately it wasn't to be so, the replacement scan coils have failed again. Same fault as before, a low resistance reading between the line and frame coils. It is now apparent what is causing the problem, the height compensation thermistor in series with the frame coils is positioned tight close to the left side line coil, not a good idea considering the high peak voltages present in the line coils. Otherwise apart from that design flaw, the line and frame coils are well insulated from each other by means of plastic spacers and cellophane. The only answer to the problem is to reposition the thermistor or remove it from the FTB circuit altogether and see what happens. DFWB.

30th Jul 2016, 6:58 pm	#29
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco T221. Your very unlucky with those coils David. I knew about the weakness with the early ones but by the time I entered the trade in the very early 60's the faulty ones had all been replaced. I have the T283 coils if you need them. John.

1st Aug 2016, 8:14 am	#30
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco T221. All is not lost David, I bit the bullet on Sunday and dragged this T283 out of loft 2. [Easier said than done but I did find some interesting items I had forgotten about..] It was minus a back and the side escutcheon. It was never going to be restored and will be a good donor to a wide range of Ekco models. I have retained all the useful bits from the chassis including the tube cradle and Mazda ReLife CRM141 CRT and dumped the rest including the cabinet. Life is too short. The scan coils and mains dropper are on their way to you this morning and I hope you have more success with these. Regards, John. Attached Thumbnails

5th Aug 2016, 4:41 pm	#31
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco T221. Hi John, The T283 scanning coils have done the trick, the T221 is working again. In the T283 pin 4 of the coils' octal plug is connected to the boost rail and in the T221 the lead goes to the chassis. It was just a simple matter of swapping the wires around. The picture quality of these sets is suburb, just as I remember almost sixty years ago a similar set on those holiday visits to Hove. DFWB.