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Old 18th Jul 2010, 9:17 am   #181
oldticktock
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Trevor,

So the components that keep dying are just old and fragile and not a by product of my ineptitude, Phew! that's a relief I posted with trepidation on this matter. What confuses me is the HT set at 205V the mains is 150V obviously I need to get up to 240V but then the HT is bonkers

The smoothers look to be orginal GEC fitted, I will check as you say.

Chris

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Old 18th Jul 2010, 9:38 am   #182
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris.
The great thing about this hobby whether you are repairing or making something you will never know what to expect, some resto's will go so smoothly others will be a pain in the a**e, but I don't need to tell you that!
One thing I tell all those new to the hobby is that it IS a hobby it's not a life or death thing and there is always tomorrow.
One thing I still do after being interested in radio & tv and as a tradesman is I still will go to bed with a Practical Wireless or TV from the 50's or a servicing book, Oh dear that sounds really sad.
Anyway keep up the good work, you will crack it, not with a hammer hopefully.
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Old 18th Jul 2010, 11:21 am   #183
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Default Re: GEC BT1156 First Light & Vidor CN4216

Quote:
I juggled the variac trying to set 205V for HT which I did but the mains was about 150V.
I don't see how the HT can be higher than the applied mains voltage.
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Old 18th Jul 2010, 11:35 am   #184
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Graham
It is possible with only 150vac that the valve heaters were not hot enough to allow the valves to conduct so the resultant HT was unloaded.
I would try it on direct mains.
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Old 18th Jul 2010, 11:47 am   #185
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Default Re: GEC BT1156 First Light & Vidor CN4216

Understood the peak value of 150V AC is about 212V, so the unloaded HT could approach that.
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Old 18th Jul 2010, 12:55 pm   #186
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Default Re: GEC BT1156 First Light & Vidor CN4216

with the metal rectifier i have mains at 240V and HT measured at 155v, Testcard on screen is formed and bright.

IN4007 with 49R mains at 190V HT reads at 205V Testcard very poor
IN4007 with 22R mains at 202V HT reads at 205V Testcard very poor

I'm at this point very confused.
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Old 18th Jul 2010, 12:59 pm   #187
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Default Re: GEC BT1156 First Light & Vidor CN4216

With low mains voltage from the variac the valve heaters won't get to the full temperature. This means they won't work properly and they won't draw so much current from the HT supply, which will rise in value.

Apply the full mains voltage and adjust the resistor in series with the diode until you have the correct HT voltage.
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Old 18th Jul 2010, 1:22 pm   #188
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Default Re: GEC BT1156 First Light & Vidor CN4216

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Originally Posted by Station X View Post
Apply the full mains voltage and adjust the resistor in series with the diode until you have the correct HT voltage.
Hi Chris
Start at 47 ohms and give the set a good 5 minutes to properly warm up before testing the HT, there has to be a proper load on the HT line to get an accurate reading, it will be about 300v on initial switch on this is normal with a silicon rectifier, so you need to wait till the HT has settles down.
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Old 18th Jul 2010, 1:33 pm   #189
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Graham,

I tried all sorts and ended up where I originally suggested in post #96 2x220R in parallel =110R that gives me HT of 205V with mains of 240V.

I'm confused as Trevor advised me that it would be way too high so I'm very confused as to what's going on here.

Chris

Edit: Hi Trevor just noticed we cross posted, can you explain because my heads all muddled now. I tried the 47R as you suggested with the mains at 240V but HT was way too high. I then tried combinations and nothing doing so I thought I would try my original plan and it's ok. Please help me understand as this is doing my nut .
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Old 18th Jul 2010, 1:38 pm   #190
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Default Re: GEC BT1156 First Light & Vidor CN4216

Chris.
Now what do you mean by way too high? Have you let the set warm up as I have explained?
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Old 18th Jul 2010, 1:50 pm   #191
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Trevor

244V at 5 mins
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Old 18th Jul 2010, 1:51 pm   #192
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Default Re: GEC BT1156 First Light & Vidor CN4216

Chris.

Could you post that part of the circuit showing the valve heaters, dropper resistor, rectifier etc. please.
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Old 18th Jul 2010, 1:52 pm   #193
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Default Re: GEC BT1156 First Light & Vidor CN4216

http://www.oldticktocks.co.uk/gec1.jpg
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Old 18th Jul 2010, 1:53 pm   #194
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Default Re: GEC BT1156 First Light & Vidor CN4216

Ok.
Is that on C137? Do you still have the set adjusted to 220v & what is the picture like at that HT voltage?
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Old 18th Jul 2010, 1:58 pm   #195
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Default Re: GEC BT1156 First Light & Vidor CN4216

TV set on 240V
Yes measured at that point
picture nice and bright, however the squiggle has returned to the top part of the testcard which was not present before. Tried line adjustment but to no avail.

7 mins in and 242V is where it stays.
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Old 18th Jul 2010, 2:05 pm   #196
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi chris.
Is the Metal rectifer still connected up cos if it is that's why your HT is too high.
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Old 18th Jul 2010, 2:07 pm   #197
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Default Re: GEC BT1156 First Light & Vidor CN4216

No its snipped out one end.

It's not connected to the CRT strap either that's the angle
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Old 18th Jul 2010, 2:09 pm   #198
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Default Re: GEC BT1156 First Light & Vidor CN4216

I reckon that with the voltage selector set to 240V all the dropper resistors are in circuit, apart from R135 which is short circuited. That's R134, R136, R139, R138 and R137. There's also the thermistor R133.

It's hard to read the values of the resistors from the diagram, but I think some have been replaced with different values. Does the measured resistance with R135 short-circuit match that calculated by adding together the values on THE DIAGRAM? You need to pull out one valve to check this.

Another factor to consider is that the HT would have been measured with an analogue meter which could have pulled the value down. In that case a DMM would show a higher value.
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Old 18th Jul 2010, 2:12 pm   #199
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Default Re: GEC BT1156 First Light & Vidor CN4216

I measured resistance before I started this but not with a valve pulled and it was 249R when set on 240V tapping
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Old 18th Jul 2010, 2:14 pm   #200
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Default Re: GEC BT1156 First Light & Vidor CN4216

OK.
Assuming that R137 & 138 (dropper sections) are in circuit and not shorted out I would try a 68 ohm in series with the IN4007, although in 40 years I have never fitted a resistor as high as that as a surge limiter, dont worry though if you land up with 210-215v HT as you seem to still have lack of width so the line stage may not be drawing full current yet. The kink at the top of the screen makes me think the line speed is out a bit still possibly still related to lack of width, perhaps low drive from the osc, pity you can't use that scope of yours, best piece of test equipment you will ever have you know.
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