25th Apr 2018, 9:54 pm | #101 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
L33 & L34 have a resistance of 20 + 8 ohms, from the Ekco sheets. I wonder if you have crossed over the ends of two windings perhaps by accident.
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Stephen _________"It`s only an old telly" ___ |
25th Apr 2018, 10:02 pm | #102 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Yep, all the HT circuitry is shorted to chassis
So far I have traced the short all the way back to - dare I say it - The coil! I'll keep you posted Edit: well the good news is the short continues past the coil so the coil can be deemed as okay Edit 2: I found the short, I soldered one of L34's wires in the wrong place Edit 3: I took a photo before I removed the old coil and it looks like the old coil was wired in the shorted position too. No idea how or why? |
26th Apr 2018, 6:53 am | #103 | |
Heptode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
It would be a good idea to have another U191 to hand, because after a 'cherry red event' a valve will often have significantly lower emission. Lets hope it still works well enough for you to properly get first light on the CRT. Cheers Andy
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26th Apr 2018, 4:59 pm | #104 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
It was wrong to drawing, one of the windings was connected to the wire that goes straight through the middle of the linearity coil to the chassis!
I'm now getting a nice big arc from the U26 anode although the valve itself is still not lighting... Peter |
26th Apr 2018, 5:06 pm | #105 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
So its suspect U26 holder or winding breaking down.
You could use an EHT diode in place of the U26, or delve into the U26 holder and wind a new coil using the inner core of coax cable.
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Stephen _________"It`s only an old telly" ___ |
26th Apr 2018, 8:10 pm | #106 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Well I rewound it using inner coaxial cable and the valve does not light, I even tried using the spare U26 I have and still nothing. I can't see how anything is preventing it
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26th Apr 2018, 8:26 pm | #107 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
With the U26 base disconnected from the the valve, can you measure the ac on the relevant pins. Make sure your winding is providing sufficient voltage.
Take care to to keep away from the u26 pins themselves whilst doing it.
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Stephen _________"It`s only an old telly" ___ |
26th Apr 2018, 8:29 pm | #108 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Hi Peter,
Well it sounds like there is a lot more energy around now, but maybe still not enough to light the U26 heater. Can you measure the screen volts and grid volts of the 30P4? Also what does the HT measure now there is a bit more load? Most important, what are the boost volts? Double check the wiring & connections to the width, linearity and both line scan coils. Make sure it agrees with the circuit diagram! Cheers Nick |
26th Apr 2018, 9:08 pm | #109 | |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
30P4 screen = 215VDC 30P4 grid = [-21VDC] I'm not really sure where to measure the boost voltage so I have a number of values. sorry if it causes any confusion. Boost cap (LOPT side) 250VDC 660VAC Boost Cap (HT rail side) 220VDC 500VAC |
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26th Apr 2018, 9:17 pm | #110 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
The voltage between the ends of the EHT winding (one of which is close enough to earth as makes no odds, by comparison) is very high, but the voltage across the heater winding (one end of which is connected to the high-voltage end) is much less. As long as both connections of your test meter are securely clipped to the heater connections, and you don't touch the meter and there is nothing made of metal within a distance of about a centimetre for every kV, it will be fine.
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26th Apr 2018, 9:26 pm | #111 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
With the U26 disconnected from the valve pins the EHT will not be present on the base, take the U26 away and do the test.
The coil you made only provides the AC needed for the heater which is at EHT potential when connected to the valve. All HT and Boost measurments should be taken as DC I think you need 1 extra turn on the winding.
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Stephen _________"It`s only an old telly" ___ Last edited by Freya; 26th Apr 2018 at 9:32 pm. |
26th Apr 2018, 9:34 pm | #112 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Sorry I'm still unsure, do you mean the wires I have circled in the picture?
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26th Apr 2018, 9:43 pm | #113 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
The winding that powers the U26 heater is a single turn of wire wrapped round one limb of the transformer. It is not connected electrically to any other winding and is completely isolated. BUT, with the U26 installed, it assumes the potential of the rectified EHT ie 16KV. This is because the cathode of the rectifier is connected to its heater. Therefore the insulation on the heater winding needs to withstand 16kV.
So without the U26 plugged in, there would be no high voltage on the heater winding. However, there would be little point measuring it with a conventional meter as it will have pulses of energy at 10Khz and the meter won't give a meaningful result. The U26 top cap, which will be dangling in free space without the valve inserted, will have a very high voltage on which would certainly kill your meter!! Your voltage readings still confirm that the line stage is not operating correctly!! The boost volts, measured on the LOPT end of the capacitor, (meter set to DC volts) is still way too low: only just above the HT of 220V. The screen of the 30P4 is too high as is the HT, indicating that the line stage is not drawing enough current. Until the line stage is working absolutely correctly, the U26 heater will not light as there will not be enough energy induced into the heater winding. Cheers Nick |
26th Apr 2018, 9:44 pm | #114 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Better to connect a 2.5v torch bulb across the winding you have circled. It should light quite brightly. The heater of the U26 is only 2V.
If the lamp does light I suspect that the voltage correcting resistor inside the base is probably O/C, disconnected or incorrectly wired. It is not a conventional resistor, just a loop of Eureka resistance wire. You may have mistaken it for a short length of non insulated wire. Quite understandable. John. |
27th Apr 2018, 10:59 am | #115 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
According to the voltage measurements it looks like there's something amiss with V16's screen circuit, only pulling just over 1mA.
Try connecting a DC voltmeter between the screen's tag on the valve holder and chassis, disconnected V16's top cap and apply power, if the voltage starts to drop below 120 volts switch off immediately. Lawrence. |
27th Apr 2018, 1:16 pm | #116 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
I just tried that and immediately after turning it on I heard a loud crackling noise, sounded very ominous not sure where it came from
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27th Apr 2018, 1:26 pm | #117 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Lawrence. |
27th Apr 2018, 1:34 pm | #118 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Luckily I tried turning it on again and I'm still getting an arc from the LOPT so that didn't go bang, still unsure what did though but I don't think I'll be able to take that measurement right now
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27th Apr 2018, 2:54 pm | #119 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Do you reckon the 0.003 Hunts cap between the 30P4 screen and the chassis is the problem?
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27th Apr 2018, 3:11 pm | #120 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
I don't know but if it's a Hunts I would replace it anyways.
The measurement I suggested was to see if the screen grids electrode connection was intact. Lawrence. |