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Ekco T344 plus another one

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Cathovisor
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@helloekco

You'll enjoy them. Websites like this are great - but I still prefer a book... 🙂 

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Posted : 19/01/2020 10:56 am
freya
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@helloekco

I would have uploaded them straight away for you but since my windows 10 has updated, now my A3 scanner wont work anymore. An A4 isn't quite big enough for the length of the Ekco sheets, they are about an inch more length than A4.

will work something out

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Posted : 19/01/2020 6:28 pm
helloekco
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@freya Thanks, there's no huge rush - it's much appreciated. The joys of perpetual Windows updates... we no longer have any control over how long our hardware goes before it's deemed obsolete.

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Topic starter Posted : 20/01/2020 12:05 am
Cathovisor
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@helloekco

A situation Mac users have tolerated for years.... 

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Posted : 20/01/2020 10:30 am
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helloekco
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I just spent a tedious afternoon going through the service sheet for the T344, producing a component list covering the caps and resistors. My eyes hurt now... I will get the component list uploaded here when I've read how to do that.

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Topic starter Posted : 27/01/2020 12:07 am
helloekco
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I got the Television Explained book, it's a really good read. The second edition I believe, dated at just the right time for my Ekco sets, 1960.

I've stocked up on capacitors, my first job on the TV is to replace any known or very likely bad caps. The main electrolytic can has some leakage at the bottom, and I've discovered what was probably the cause of the smoke when I powered the set up months ago, there's a pair of wax caps on the front of the chassis, the top one has partially melted onto the bottom one.

One thing I'm unlikely to find is the correct mains power connector. Does anyone have any recommendations? It's got two round pins of differing sizes. I was thinking of making up a connector from a block of wood or perpex, drilled out, and containing two of those female connectors often used in car electrics (assuming I could get the correct sizes). I realise another option would be to dispense with the removable connector altogether and permanently solder a two core flex to the TV.

Skipping forward a bit, I've read that when powering up a set for the first time, it can be done with the EHT rectifier removed, to first check that the timebase etc is running. Does this pose any risk to the health of the LOPT?

A general question - what do people use exactly to discharge EHT from the tube. I've read about using an insulated screwdriver, but there are none that claim to insulate up to 15kv! How much risk of shock is there if only contacting the TV at one point (and also when running on an isolating transformer, not that that is relevant to the EHT which has its own).

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Topic starter Posted : 30/01/2020 11:37 pm
freya
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I have made up a couple of the mains plugs using the metal inserts from choc bloc connectors. These are available in the correct sizes for the pins on the mains connector, and you could use one of the screws  to attach the mains lead. These are moulded into resin to create the insulted plug.

For powering up the set, I always have used the directly powering method, its personal choice. If your sets have been kept in dry conditions then there is no reason why you should not power up with the EHT connected. It wont damage anything to disconnect the EHT rectifier. To discharge the EHT, short the EHT anode cap to chassis using a well insulated screwdriver or test lead. Even wear rubber gloves if your concerned. 

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Posted : 31/01/2020 2:38 pm
Nuvistor
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One of the biggest dangers of small BW CRT’s being left with a charge is dropping it whilst carry it. I only ever discharged the CRT if working in that area or replacing one.

 

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Posted : 31/01/2020 5:44 pm
helloekco
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Thanks both, that’s helpful.

I’ve been getting a bit paranoid about the tube implosion risk. I haven’t separated it from the chassis as it looks as though there is enough room to work on the front of the chassis (just). Should I be concerned about e.g. a droplet of hot solder contacting the back of the tube? I thought of covering it with a sheet while soldering.

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Topic starter Posted : 31/01/2020 6:52 pm
Nuvistor
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The bulb area is quite strong, it’s the neck and pip under the base that are the weak points. Of course hit any part with a strong blow can cause much grief.

If you decide to handle the CRT, gloves and goggles are recommended. 

 

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Posted : 31/01/2020 7:18 pm
helloekco
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Thanks Frank. What I am going to do is rearrange my working area, as I’ve realised what a very bad idea is it to have the naked chassis and CRT below a shelf with some stuff on it! 

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Topic starter Posted : 31/01/2020 7:38 pm
helloekco
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I had quite an encouraging evening on this. After replacing the main electrolytics, all the wax paper caps I could see, and a valve, and removing the EHT rectifier so I had less to worry about, I tried applying power.

At first I had some heater chain weirdness. One of the valves glowed bright white so the power was swiftly killed. I took it out and noticed that it was installed the wrong way around with the one next to it (V1 / V2). When I applied power again, nothing. After a lot of messing around measuring heater chain resistance to try and find the open circuit, I suddenly started getting continuity again between valve sockets I'd already checked... God knows what that was about. On a hunch I applied power again and the heaters were back.

I got the voltage up to about 220v on my variac and I got what sounded like quite a healthy line whistle! However, there was a crackling sound which I knew as the sound of something melting, and luckily I could just make out the end of a wax cap that I'd missed, bubbling away in the bottom of the set. So it will have to wait until another day.

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Topic starter Posted : 05/02/2020 12:42 am
freya
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Great work so far !

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Posted : 05/02/2020 2:48 pm
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helloekco
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I had a bit of a disappointment tonight.

After replacing the melted wax cap I got the set powered up on full voltage for a good few minutes, no signs of smoke, and a nice line whistle. Crackling from the temporary speaker I've wired in, so it sounds as though the audio amp is working of sorts.

I went ahead and refitted the EHT rectifier, but nothing from it - no heater glow. I remove it and checked the heater for continuity and it's OK, but I left it there for tonight, so I haven't yet checked the anode with a neon screwdriver in proximity for instance. I don't think the whole LOPT is at fault because there was a strong blue glow from the line output valve, V16.

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Topic starter Posted : 06/02/2020 12:04 am
Nuvistor
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A strong blue glow, there can be a bit a blue glow but a strong one too me seems a problem. Depends can how strong.

If you have a scope check the line drive frequency and expect about -35 to -40 volts on the output valves G1, measured with something like an Avo 8.check the screen feed G2 components.

There may be a resistor in the U26 base for the heaters, possibly O/C.

 

A neon for testing a valve  line stage, I better not say what many of us did to test the stage. ? 

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Posted : 06/02/2020 9:31 am
freya
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Hi Chris,

 

A strong blue glow from the PL38 is not normal, also can you confirm if you have the set connected to a signal. 

 The reason I ask is that if your line frequency may be off by a long way and you may not see the EHT rectifier heater glow.

 

Stephen

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Posted : 06/02/2020 9:32 am
Nuvistor
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Another thought about the EHT rectifier, I am presuming it’s a U26 not U25. The valve bases can corrode and go green, if it’s a McMurdo type the individual socket clips break off.

 

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Posted : 06/02/2020 9:36 am
freya
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I should have said 30P4 not PL38 ? 

 Notice my avatar has a U25 that's got a nice blue glow about it.

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Posted : 06/02/2020 9:53 am
Cathovisor
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Posted by: @helloekco

I don't think the whole LOPT is at fault because there was a strong blue glow from the line output valve, V16.

There is the possibility that the line output valve is merely 'soft': to my mind, a blue glow points to ionisation rather than an overload. Is it possible to do a quick 'ring test' of the line transformer?

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Posted : 06/02/2020 10:31 am
Nuvistor
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A faulty valve is very likely correct, I didn’t know if there was a spare available so suggested confirming drive etc was correct.

I don’t know how the transformers have stood the test of time but the only two faults I had with them was the housing material crumbling and occasionally had to rewire the heater winding.

 

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Posted : 06/02/2020 10:56 am
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