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Old 13th Mar 2021, 5:59 pm   #41
19Seventy7
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Default Re: GEC BT302 Television restoration

Hi all

I’m sure I remember reading somewhere that you can record a 405 line picture onto VHS, play it back in a VCR onto a 405 line TV as long as there’s a VHF converter?

I’ve searched for it on here but I can’t find any results. Is that possible, or am I making it up? If so would anyone be able to record a test card onto VHS? I’m happy to pay for it and can send a blank tape. I’ll be getting a standards converter, but it’ll be a few months away now so would be nice just to get something up for now, even if it’s not perfect, just to see what I’m dealing with

Thanks
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Old 13th Mar 2021, 6:15 pm   #42
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Default Re: GEC BT302 Television restoration

Yes, recording onto VHS was a method that enthusiasts used before standards converters became available; a System A modulator to convert to VHF was still required though. Although this is much easier to make than a standards converter it is still not a simple matter. Also, it was only some early video recorders that happened to work on 405 lines, later ones wouldn't.

The Aurora and Hedghog, although referred to as "standards converters" also have the modulator built in.
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Old 13th Mar 2021, 6:35 pm   #43
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Default Re: GEC BT302 Television restoration

Ah right, won’t work for me then as I’m using a 2000s VCR, and I probably wont be able to make a proper System A converter. It’ll probably we worth waiting then

Thanks for the help, much appreciated
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Old 12th Jul 2021, 6:16 pm   #44
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Default Re: GEC BT302 Television restoration

Hi all

So I've got an update. I've got a standards converter now and hooked it up to the GEC straight away. I've got a funny looking test card. I've never seen anything like this before from a TV so have absolutely no idea what to do or look out for.

All hunts capacitors have been replaced and the two electrolytics. I thought I'd swap the frame output valve over, which has given no improvement, not that I really expected one.

I'm happy with the results so far though!

Any ideas at all? I've had a pretty extensive search on this forum and VRAT but haven't been able to find anything that would relate to this problem.

EDIT: Could the title be changed to GEC BT318 please, I got the models mixed up and have only just realised... Oops!

Thanks
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Old 12th Jul 2021, 6:54 pm   #45
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Default Re: GEC BT302 Television restoration

Have you tried twiddling the vertical hold control?
Also the two pre-sets above it, "height" and "vert. form"
There is probably an electrolytic on the cathode of the frame output, change it.
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Old 12th Jul 2021, 8:23 pm   #46
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Default Re: GEC BT302 Television restoration

Twiddling vertical hold can get me a larger picture, but the image will scroll, this is the only stable image i can get, height and vert form both only seem to adjust the height, and they're both at max in order to get an image this size.

I think I changed that electrolytic, 250uF 50v? I replaced that with a 220uF which did cure a fault of the speaker squealing while the valves warmed up

Thanks
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Old 12th Jul 2021, 8:39 pm   #47
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Default Re: GEC BT302 Television restoration

Something running at the wrong speed in the frame section....could be more than one fault. This is where a scope is useful if you have one. Without one you will have to firstly check that any capacitors you have replaced are a) the right value and b) in the right place. Check resistors in the frame oscillator stages....take note that some values of resistors and capacitors in the frame oscillator may be critical.
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Old 12th Jul 2021, 9:12 pm   #48
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Default Re: GEC BT302 Television restoration

Unfortunately I don't have a scope, which makes things tricky..

I'm fairly sure that all caps are correct in both value and position, as i replaced them one by one. I did connect two to create another value, I put two 0.01uFs together in hopes to create 0.02uF but im not sure if it could've made 0.005uF. Its made out of those yellow poly axial capacitors. I'd have thought this would double the capacitance?

I've also noticed I've fit a 0.47uF in place of a 0.1uF cap, really not sure why. I think that could very well be what's at fault here? I have a .1uF on its way


Thanks
'77

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Old 12th Jul 2021, 10:15 pm   #49
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Default Re: GEC BT302 Television restoration

Two 0.01uFs in parallel will give 0.02uF. If you put them in series you will get 0.005uF.

It's the opposite way round to how resistors combine.
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Old 12th Jul 2021, 10:28 pm   #50
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Default Re: GEC BT302 Television restoration

The 0.01uFs aren't polarised, so i just connected to random ends, though if we were to judge by their writing they're in parallel.

I'd have thought it would double to 0.02uF

Thanks
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Old 13th Jul 2021, 12:57 am   #51
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Default Re: GEC BT302 Television restoration

Quote:
Originally Posted by 19Seventy7 View Post
The 0.01uFs aren't polarised, so i just connected to random ends, though if we were to judge by their writing they're in parallel.
You are correct that the orientation of the capacitors is not important, but that does not determine whether they are in series or parallel.

So for the avoidance of doubt.

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Old 13th Jul 2021, 1:09 am   #52
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Default Re: GEC BT302 Television restoration

Oh thank you! That clears things up massively think I have them in series then, i just twiddled the legs together, soldered them, and then soldered the other legs of each cap into circuit.

I'll take a look at it again tomorrow and see if I can put them in parallel, should be easy enough.

Thanks for clearing that up, much appreciated!
'77
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Old 13th Jul 2021, 3:52 pm   #53
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Default Re: GEC BT302 Television restoration

Deja vu. Check all your components for correct value and positions on board. No scope required. Good luck with it. John.

https://www.vintage-radio.net/forum/...ight=GEC+BT302
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Old 13th Jul 2021, 7:14 pm   #54
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Default Re: GEC BT302 Television restoration

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Originally Posted by Heatercathodeshort View Post
Deja vu. Check all your components for correct value and positions on board. No scope required. Good luck with it. John.

https://www.vintage-radio.net/forum/...ight=GEC+BT302
I remember that thread too, I don't think many people will forget it any time soon..

I've gone through it with the manual and made sure they're all right, just my novice mistake of connecting the .01uFs and the .47uF. Still haven't a clue how i mixed that up. I must've just had it in stock and thought i'd try it

Thanks
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Old 13th Jul 2021, 8:44 pm   #55
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Default Re: GEC BT302 Television restoration

The pic in #44 shows the timebase locking at 100Hz. The field frequency is 50Hz, the same as the UK mains. TVs had basic half wave rectifier with smoothing, some also an HT choke. Although the ht line is dc there might be a small 50Hz ripple, and a slight ripple is often present caused by the field output stage. Although the result may not be visible, if you turn down the volume and listen to the speaker, you will hear the field pulses. Also
the field output transformer may have a buzz at 50Hz that can be heard.
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Old 13th Jul 2021, 8:54 pm   #56
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Default Re: GEC BT302 Television restoration

No you need to swat up on the difference between resistors and capacitors in parallel. Capacitors in parallel increase in value, resistors in parallel reduce in value. Capacitors in series reduce in value, resistors in series increase in value. Don't mess about with the values of capacitors particularly in the frames stages or you will get nowhere. Fit the right values.
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Old 13th Jul 2021, 10:07 pm   #57
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Default Re: GEC BT302 Television restoration

I had only mixed these two as I couldn't find any 0.2uF so the best I could do was fit some together. I'd never done it before so wasn't sure how it'd work. The way i did it I thought would work as it'd be travelling through 0.01uF, and then another 0.01uF thus making 0.02uF, but my logic was wrong. Thats something learnt for sure.

I've replaced the 0.01uFs so they should now be making 0.02uF, waiting on the 0.1uF to arrive though and we'll see how that works out.

Apologies for such a daft mistake, i've definitely learnt my lesson though!

Edit: Sorry Restoration73 I didn't see your reply

Can't say I have heard the buzzing but ill have a listen next time the set is on

Thanks
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Old 14th Jul 2021, 8:24 pm   #58
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Default Re: GEC BT302 Television restoration

Quote:
Originally Posted by 19Seventy7 View Post
I had only mixed these two as I couldn't find any 0.2uF so the best I could do was fit some together. I'd never done it before so wasn't sure how it'd work. The way i did it I thought would work as it'd be travelling through 0.01uF, and then another 0.01uF thus making 0.02uF, but my logic was wrong. Thats something learnt for sure.

'77
Dejavu indeed I am sure we have had this conversation once before in your G8 thread
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Old 14th Jul 2021, 8:52 pm   #59
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Default Re: GEC BT302 Television restoration

Now we're getting confused over values. You said you couldn't find any .2uF. For a .2uF you would need two .1uF in parallel. For .02uF you would need two .01uF in parallel. So do you need .2uF or .02uF.

Make sure the values you use are correct...
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Old 14th Jul 2021, 9:56 pm   #60
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Default Re: GEC BT302 Television restoration

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Now we're getting confused over values. You said you couldn't find any .2uF. For a .2uF you would need two .1uF in parallel. For .02uF you would need two .01uF in parallel. So do you need .2uF or .02uF.

Make sure the values you use are correct...
Apologies for that, that was a typo, I even went back to make sure I had got them all right but missed that one. I do definitely need 0.02uF, which I've made up.

The 0.1uF (to replace the 0.47uF) hasn't long arrived so I'll be fitting it in a second and seeing what difference it makes.

Apologies for that confusion.

Quote:
Dejavu indeed I am sure we have had this conversation once before in your G8 thread
We sure have haha, I had actually recapped this set a while back, way before the G8, but I could never get life out of it, so put it back for a while and worked on the G8 while I could find some more info on this set.

This thread has actually taught me a lot, so thank you all, and that I've also done it wrong in the G8, while they are technically in parallel, I'd misunderstood how it works and had connected the negative leads together, but thread each positive lead of each cap into the two PCB holes, so the negative leads aren't in circuit - I did wonder how it'd work like that...

I'll soon be going over that error.

I'll have to apologise all, I've never really worked with capacitors like this before (other than the G8 and messing that up) so this is all very new to me, so I thank you for your patience too - I know I must be testing it a bit at times... Sorry!

I'll let you know how replacing the caps with the correct values goes

Thanks
'77
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