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Ekco T344 plus another one

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Till Eulenspiegel
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Hi Frank,  the PL36 could be used as a substitute for 30P4/19.  If there are any non line timebase components anchored on certain tags on the valve socket these must be removed. I remember in T330 models if a PL36 was plugged in the vision AGC didn't work. 

Till Eulenspiegel.

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Posted : 06/02/2020 9:06 pm
Nuvistor
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I think the 30P19 was a direct replacement for the 30P4 but I do remember the PL36 was a problem. From memory this set used a printed circuit board for the line output and boost diode, not sure if that makes removing connections more of a problem.

Like most of the sets of this era the makers had sorted out how to get the best performance and they gave a really good performance.

i  can’t remember if I used 30P19 to replace a PL36, I was lucky the boss allowed me to have a comprehensive set of spares. He did the job before me and how having the right gear and spares made life much easier. A bit of a nostalgia trip but he was a really good bloke, died March 1979. 

 

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Posted : 06/02/2020 11:10 pm
Till Eulenspiegel
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Hi Frank, in the KB VC series either the PL36, 30P19 and Brimar PL302 were fitted  in production.   30P19 replaces 30P4 direct, except in the Murphy V310 with the self oscillating line output stage. Fit 30P4MR.

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Posted : 06/02/2020 11:25 pm
Till Eulenspiegel
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Hi Chris,   for your T344. If you would like a NOS PL36 FOC to try out in the set you are welcome to one.   Got some Mazda PL36 valves here which were made in the DDR.   Send me a PM if you are interested.

Till Eulenspiegel.

 

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Posted : 06/02/2020 11:42 pm
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helloekco
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Hi,

I probably overstated the 'strong' blue glow of the 30P4 - only internally inside the anode, much like something such as an EL34 in an amplifier. But it seems to vary a lot when the horizontal hold is adjusted, which I didn't try yesterday, going to practically nothing at some settings.

I did apply a signal to the set tonight when testing it, but I can't tell right now whether it's set to the correct channel as the cabinet and knobs are put away in the attic! My modulator is channel 1 only and I'm not sure whether the TV's channel selector stops at channel 1 or rotates past it, I tried changing it a few times with a pair of pliers but it's tricky; I didn't get any sound coming through.

I tried the neon screwdriver thing and I was quite shocked (not literally) to discover how far away the tip could be, while getting a bright glow from the lamp! So I think it's safe to say the EHT voltage is quite healthy. (Frank, did the other way involve making an arc with a screwdriver? ? )

Luckily I have the other set to borrow valves from, but I tried each of the 3 associated with the LOPT and they didn't make any difference. Obviously I have no idea whether those are any better.

However, I think it is possibly just the line frequency that's out. If I turn the horizontal hold completely anti-clockwise so that the whistle is at its highest pitch, with the room light turned off, I can just about make out the EHT rectifier heater glowing - and there is a very clear blue ring inside. I definitely think it's doing something, because in frustration I gave the base of the rectifier socket a prod with a screwdriver and there was a spark! That's what led me to look more closely. I've attached a photo, unfortunately it's only taken with my phone and it doesn't make out the heater, just the blue glow. When I'd finished I checked for warmth from the rectifier and there was none; what kind of current does the heater draw on these, should it get hot like other similarly sized valves? (I was surprised when I realised that the heater winding is merely a couple of turns around the outside of the transformer!)

IMG 0987

 

Unfortunately my scope is too buried beneath stuff to dig it out tonight, but I think the next thing as you suggest is to check the line output frequency.

@Cathovisor - what do you mean by a ring test of the LOPT?

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Topic starter Posted : 07/02/2020 1:01 am
helloekco
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I didn't see all the later replies until I'd posted the above, the valve I tried from the other set (T344F) was indeed a Mullard PL36! I'll have to check whether that has modifications.

I also forgot to say in the previous post that the pins on the rectifier were indeed quite green, but I gave these a good clean with Deoxit, and the socket too. The socket heater pins seem to have good continuity.

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Topic starter Posted : 07/02/2020 1:05 am
Nuvistor
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The U26 has a 2v 0.35ma heater and max anode current is 0.2ma, it will not be much hotter than the surrounding area.

The 2v heater is why there are only a couple of turns around the LOPTX core, the TV sets that use an EY86 with a 6v heater obviously will have more turns. The heater winding is at EHT so needs well insulated wire.

 

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Posted : 07/02/2020 9:31 am
Cathovisor
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Posted by: @helloekco

@Cathovisor - what do you mean by a ring test of the LOPT?

I mean this - www.radios-tv.co.uk/333-2/

Because it's an inductive device, if you apply a fast-rising signal to it, it will resonate - or, 'ring'. If anything exists to damp that resonance - for example, a shorted turn - the 'ring' will be greatly diminished or even absent.

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Posted : 07/02/2020 11:46 am
Till Eulenspiegel
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Circuit diagrams of the line timebases in both versions of the Ekco T344.

EkcoT344 flywheel sync
EkcoT344 diect sync
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Posted : 07/02/2020 2:32 pm
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freya
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The full manual for all versions is in the data library.

 I may have a transformer should it prove faulty but would need the SA number to verify a match.

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Posted : 07/02/2020 4:00 pm
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helloekco
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Posted by: @cathovisor
Posted by: @helloekco

@Cathovisor - what do you mean by a ring test of the LOPT?

I mean this - www.radios-tv.co.uk/333-2/

Because it's an inductive device, if you apply a fast-rising signal to it, it will resonate - or, 'ring'. If anything exists to damp that resonance - for example, a shorted turn - the 'ring' will be greatly diminished or even absent.

Great article, thanks. I'm going to try and avoid that for now though, as I'd rather not take the transformer out of the set if possible. It looks a bit tight for space to disconnect it and leave it in situ. Also, I don't have a known good one to refer to, although it looks as though a problem one would be fairly obvious from the rate of decay vs the wavelength.

I got the scope on grid 1 of the 30P4 line output valve and this is what it showed:

Photo 07 02 2020, 23 56 50

The voltage looks about right (-30v-ish), the frequency just about high enough (the scope was set to 100u sec / cm), although the horz hold was almost as far as it would go anti-clockwise, but should those waves be flat like that? The flat part is at 0v. The scope was set to AC, I don't know whether that should make a difference.

Given that waveform, I'm tempted to go around some of the other caps and the resistors on the timebase board - I only changed the obvious larger paper ones.

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Topic starter Posted : 08/02/2020 1:34 am
sideband
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If you try the ring test and get a nice healthy 'ring', just as an experiment make a loop of wire just big enough to loop around the transformer and with the ring displayed on the scope, short the ends of the loop together and see what happens to the ring....only one shorted turn will make a dramatic difference......

That was one of the first things I was shown when I entered the trade at 17. 

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Posted : 08/02/2020 8:00 am
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Nuvistor
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This is the waveform at G1 of a similar circuit, it’s from a later Bush TV135 dual standard. The wave shape is near identical to yours. Ekco rarely gave scope waveforms, not many of us had them in the late 50’s early 60’s. 
The flat portion of that wave will be the grid cathode circuit clamping the voltage, hence the -30 odd volts.

Hope I have that correct, digging into the past for that information.

If your line osc is off frequency it would be worth sorting that out.

 

224B1AC3 F2E0 4BCC B510 A4E5F76FC5A9
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Posted : 08/02/2020 9:39 am
Till Eulenspiegel
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The drive waveform should be negative going, that is, below the zero line indicated when the scope input is switched to D.C. -30V P - P is too low. Also, I notice that the top of the waveform is rather "flat". Check the 0.01mfd coupling capacitor again. Scanning repetition rate should 100micro-seconds. 98.8 when synchronised to a 405 line signal. 

Till Eulenspiegel.

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Posted : 08/02/2020 11:26 am
Nuvistor
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Ah, perhaps I read that incorrectly, I thought it was -30v on the grid measured with an Avo, yes P-P is too low. I seem to remember about -40v measured with an AVO was nearer correct.

The P-P voltage on the RBM diagram is 150v.

 

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Posted : 08/02/2020 11:33 am
Cathovisor
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Posted by: @nuvistor

The flat portion of that wave will be the grid cathode circuit clamping the voltage, hence the -30 odd volts.

Hope I have that correct, digging into the past for that information.

Spot-on, Frank ? 

"Leaky-grid" detectors wouldn't work otherwise!

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Posted : 08/02/2020 11:54 am
helloekco
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Thanks for that Frank - in my ignorance I assumed that I would be looking for a perfect sawtooth on that waveform. And yes, it was roughly just under -30v to the peaks, so I think I have something to go on there.

Till - yes it was that flat part of the waveform that I thought looked wrong. I will check the coupling cap to start with.

I'll also hook up a 10khz signal to the second trace on my scope for comparison and check this again. I was using my valve scope for this and its accuracy is dubious (I had a hell of a time getting the trigger stability to hold for long enough to take that photo - perhaps my next project after the Ekcos).

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Topic starter Posted : 08/02/2020 3:41 pm
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Till Eulenspiegel
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The line output valve functions as a switch and is turned off at the start of the forward scanning stroke. It's on the latter 60% of the forward scan the valve is turned on hard and current ramps up in a linear manner in the line output transformer. The first 40% of the scanning stroke is derived from reclaimed energy from the flyback. The U191 diode is used for that function.

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Posted : 08/02/2020 5:56 pm
PYE625
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Slightly jumping the gun a little maybe, but when you do get the line stage operating as it should (not far off me thinks ? ) you may find the full EHT could be a problem for the Metrosil if it looks anything like mine did....

rsz img 2618

 

It is a device mounted in a plastic tube to the left of the chassis viewed from the front.

rsz img 2610

If it is broken or in poor condition, the EHT could arc inside the plastic tube. I completely removed the one from my set as it was corroded and falling to bits. The Metrosil is meant to regulate the EHT level, but in reality, it will not greatly affect performance if it is removed.

If, on the other hand, your one is in good condition, then of course leave it in place. It will help to discharge the EHT when the set is switched off.

Another thing to be mindful of is the fact that the metal shroud on the base of the rectifier U26 will sit quite nicely at full EHT (around 15kv) waiting to give you a nasty tickle if your hand (or any conductive object) should be too near.... I speak from bitter experience !

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Posted : 08/02/2020 11:14 pm
PYE625
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Posted by: @helloekco

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.

Please DO NOT go near the line stage valves or transformer with a neon screwdriver. It may conduct heavily at the high voltages and give you a nasty burn.

Don't want to teach my grandmother to suck eggs, but thought I better say just in case anyone who is reading may not know the high voltage risks involved.

 

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Posted : 08/02/2020 11:34 pm
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