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Old 27th Apr 2022, 10:14 pm   #1
alfatangowhisky
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Question Ekco T368 / T370 LOPT connections

Good evening all.

I know these LOPTs have been discussed a fair number of times already but none of the existing posts seemed to have an answer to my question, which is, simply - what wire goes where?

As we know these LOPT cases like to turn to dust (and to add my 2p worth, I have burned a bit of the remnants and would say the smell that comes off is very similar to old polyester resin - reminds me of a time in my school days where I cut up some 1960s shop mannequins for an art project, and they had the same smell when a saw blade was taken to them). Anyway, I digress.

Since I have been dealing with a very discombobulated casing and at the time thought I had marked all the connections up for when it was time to re-assemble, now coming to the re-assembly I find that I am not 100% sure I have the full picture of which wire from the LOPT windings goes to which solder terminal (having de-soldered them for cleaning).

I have worked from some pictures I have taken and the Trader sheets (so any component references you see me make are theirs), but I find transformer diagrams, especially LOPT ones, to be sometimes a little bit cryptic.

Having also traced back on the chassis to some prominent components I do believe that I have matched the correct wires up, but would appreciate if those who have a working LOPT could please check my attached diagram to confirm, or not.

I have tried to use the wire colours that are in my set, but the grey for example seems to have come making it look like black.

There is no casing - that is still to be made - but in the image I have 'floated' the solder cups in their relative positions.

So, did I get it right?
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Old 28th Apr 2022, 10:50 am   #2
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Default Re: Ekco T368 / T370 LOPT connections

I took this picture this morning of the line output transformer in the Ekco T377. It is the same chassis as the T368 but has a 19" tube. It shows the connections, the only difference being that the black wire on your drawing [bottom right] is a white wire on the T377.
Don't forget to check the 27K bias stabilizing resistor from the HT line to the cathode of the video amplifier. It often reduces in value giving some very odd effects. Hope this helps. Lovely receivers spoiled by the Mazda CME1703 CRT that lost it's sparkle after a couple of years. It lingered on never really getting any worse but the high quality picture never returned unless the tube was changed! Picture of T377 picture. John.
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Old 28th Apr 2022, 2:39 pm   #3
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Default Re: Ekco T368 / T370 LOPT connections

Thanks HKS(John). I am happy with the external wires (to other parts of the set). What I am not 100% confident with is the lacquered wires emanating from the LOPT windings, in relation to which solder 'button' they arrive at.

I think my wire which shows as Black, which was meant to be Grey is in fact a dirty White so is identical to your images.

BTW, my set came with an AW44-88 fitted so high hopes for a good picture.

Will show you when I get it working!


Cheers

Adam
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Old 28th Apr 2022, 2:47 pm   #4
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Default Re: Ekco T368 / T370 LOPT connections

The Mullard AW43-88 will be OK. It was probably replaced years ago. The windings leads should fall into place. John.
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Old 1st May 2022, 10:46 pm   #5
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Default Re: Ekco T368 / T370 LOPT connections

Yes, AW43-88 (typo!)

Well, I have cobbled something together, nothing like John's pristinely preserved example but I hope functional.

Had a bit of a scare when one of the wires snapped, right where it goes into the laminations, as they like to do! But I dug in a little bit and soldered some a new tail on.

The framework is made from a section of a section of pre-punched tagboard: https://secure.presspahn.com/Cart/15...d-298mm-x-45mm

(BTW, good company to deal with for source of Paxolin and material from which they take their name - Presspahn - which I intend to use to make a new cover piece for the legend plate / PCB cover under the hold, height etc. controls which has cracked and crumbled due to heat)

This tag board was cut to size, the original holes widened where needed, and pop-studs, which are used in dressmaking etc, became my solder cups (they normally are closed at one end but I punched through to make them feed-through). These tin very well. They were pressed into the ever-so-slightly undersized holes that I drilled.

I put the wide, most corona-proof sides the back of the assembly and when everything is working to my satisfaction I will spray the front side, which has more sharp edges (from the punching and swaging), with EHT lacquer.

The tag board was mounted into the two bottom original screw points via stand-offs. The reduced size of the rig compared to the Ekco original meant that the leads from the output and efficiency valves did not reach to their new locations so I re-made them with longer wire.


The set had the X-cap replaced and power was applied via a series of limiting lamps. All that I can manage (except speaker hum and less than 100v HT measured at tag 10 running set at 230v with a 150W lamp) is a strangled line whistle (I'd actually struggle to call it a whistle, maybe more like a purr) which can be made to change pitch when rotating the line hold control. This also varies the HT by around 5v from one side of the setting range to the other.

There is a very small spark on both top caps. There is no line sound whatsoever with the 30P4 top cap removed.

Having made sure again that I have all my wiring correct I can only suspect some other timebase component is at fault. Other sets when run under these conditions still do whistle, feebly. This sounds more sick.

More updates when I get chance in the week ahead...
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Old 2nd May 2022, 7:53 am   #6
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Default Re: Ekco T368 / T370 LOPT connections

All the wax caps will need changing. The lack of HT is probably due to the smoothing block reservoir section being O/C. The PY32/33 maybe low but I doubt it especially if it has a PY33 fitted. The low HT if not the main cap is probably due to badly leaking wax caps in the line output stage. Start with the boost cap and line coupling capacitor to pin 5 of the 30P4.
John.
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Old 4th May 2022, 7:08 pm   #7
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Default Re: Ekco T368 / T370 LOPT connections

Smoothing cap (100 + 200) was measuring more like 2 + 4; changing this got rid of the sick line whistle (must have been a lot of AC getting into HT).

Changed all the wax / 'wax in disguise' / crusty Metalmite / crumbly Hunts caps and now I have a frame collapse line so first light!

Seems LOPT connections are all in order.

I also found the attached image (from VRAT I think), showing a Ekco LOPT casing split down the middle and the wiring very visible, eminently useful in convincing myself that I had all the connections right.
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Old 7th May 2022, 12:43 pm   #8
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Default Re: Ekco T368 / T370 LOPT connections

Unusual to get a total frame collapse on the Ekco 300 series. Check you capacitor connections. Did you replace the lot in one go? If not did you get any form of scan after repairing the transformer? J.
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Old 10th May 2022, 6:30 pm   #9
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Default Re: Ekco T368 / T370 LOPT connections

Just to be sure on the connections, here is the T370 lopt part of the diagram with ID for the leadouts.
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Old 10th May 2022, 6:50 pm   #10
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Default Re: Ekco T368 / T370 LOPT connections

Thanks Freya. I can confirm it is all connected up fine.

The frame collapse was due to an exhaused 30PL13. There was maybe 1/8" frame height after 5 minutes but it wouldn't improve so was replaced by a 30PL14 which gives loads of height.

Now running fine sorting out the last bits like a bit of top foldover. CRT is wonderfully sharp with plenty of definition on the test card.

Is a 30PL14 considered a suitable replacement for a 30PL13 ? It isn't listed as such yet has nearly the same characteristics, and the same pinout and construction looks identical.
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Old 11th May 2022, 8:38 am   #11
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Default Re: Ekco T368 / T370 LOPT connections

Just in case you missed it, don't forget the frame lin preset in the top right hand corner of the P/C board. J.
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