Ekco T344

[Radio Tech]

Hello Frank,

The slow appearance of the picture was mainly down to video drive and the culprits were a combination of both resistors that had gone high in value and valves that dealt with video signal, just a matter of replacing the temporary shroud that I made for the LOPT of which I made from cardboard, now made one in plastic, and a 270 Ohm resistor R72 with a better wattage and then back into its case and one more final check.

The heater voltage on the tube sits around 10.5V, tube heater voltage for the CME1703 is 12V, I think the slight difference is due to the mains dropper resistances not being quite what they should be. The values are 33R (reads 37R) 66R (reads 67R) tap between 3 and 4 66R (reads 71R) 12.5R (reads 13R) 25R (reads 27R) 50R (reads 52R)
This was taken from tag 1 on the dropper and working upwards.

Best wishes

Ken

[Nuvistor]

With it being series chain you could check that the current is within limits and check the CRT again. I don't have a Mazda book to hand but the Brimar specification for series heaters tolerance plus minus 5% max.
It's coming along nicely.
Frank

[Radio Tech]

Hi Frank and everyone who contributed to advice,

I have now re built the shroud on the LOPT and with a few other resistors that I found had gone high, and most of the valves in the video signal chain replaced the set appears to be working well. I did get bitten twice by the EHT that hadn't finished discharging though when the set was off and not I might say connected to the mains, 15kV takes a fair while to die away on its own from the anode final of the tube.

Here are two or three pictures of the set, you will notice that the majority of the trouble was around the frame and line time base section.

Best wishes

Ken

[Nuvistor]

Excellent, these sets can produce a very good picture.

[Freya]

Nice result ken, well done. Good looking shroud.

[Lloyd 1985]

That is a good result! Tube looks nice and bright. Nice job on the LOPT housing. One thing I noticed with my T368 was that the base of the EHT rectifier is fitted into a metal bell (I think that best describes it?!), and this 'bell' is at full EHT potential! I was quite surprised at that, certainly one to watch out for if you have already gotten a nip from the EHT!

Is the Metrosil present in your set?

Regards,
Lloyd.

[Nuvistor]

Originally Posted by Lloyd 1985

One thing I noticed with my T368 was that the base of the EHT rectifier is fitted into a metal bell (I think that best describes it?!), and this 'bell' is at full EHT potential! I was quite surprised at that, certainly one to watch out for if you have already gotten a nip from the EHT!
Regards,
Lloyd.

The anode of the U26 is just as bare, just something we accepted and kept away from.
Frank

[Lloyd 1985]

Yes, I just wasn't expecting it, I thought it was plastic, and noticed it was metal when I was cleaning it up.

Regards,
Lloyd.

[Radio Tech]

Hi LLoyd

The metrosil broke in mine and I just took it out, Dave from the museum of sounds of the past who is a retired TV engineer told me to take it out, the metrosil is supposed to give some form of regulation but they never do. I have got the ally shield that covers the area where the EHT section is, just got to put it back.

Regards

Ken

[Nuvistor]

Metrosils didn't get replaced in general, some may have replaced them but I didn't. If they did improve the regulation is was so little most didn't notice.
Frank

[Radio Tech]

Hi Everyone,

Just one final picture of the set in its cabinet and the set displaying the all time famous test card (without the BBC logo).

Best wishes

Ken

[Nuvistor]

Got there, well done, looks good and it must be near 60 years old.

Frank

[Lloyd 1985]

Looks good in its cabinet!

Regards,
Lloyd

[The Philpott]

Excellent, this is why I didn't want to tackle it myself- it took an expert a month of evenings!

I am just glad the tube wasn't u/s.

[MonochromeMarc]

A fine job done and looking good

Marc.