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3rd Nov 2020, 1:14 pm | #21 |
Heptode
Join Date: Aug 2009
Location: Carshalton, Surrey, UK.
Posts: 735
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Re: Ideas needed to build a new 'old TV'
HI,
this thread is most useful ( as is the mention to the personal televisor Nov 52 in PT ) as I have a 3bp1 crt as part of a frankenscope. The mention of using push pull drive to the crt is a good one.
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Regards Peter B |
3rd Nov 2020, 1:32 pm | #22 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
Does this mean another potential builder?
Adrian |
3rd Nov 2020, 1:49 pm | #23 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
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Re: Ideas needed to build a new 'old TV'
Quote:
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-- Graham. G3ZVT |
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3rd Nov 2020, 10:27 pm | #24 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
OK to answer my own question in post 20 I have oput together the Line timebase circuit with the EF91. The measurements show in the article that a 225 Volt HT is expected, so have stuck with that.
The valve oscillates away happily, so I was reading part of the article on the oscillator wrong, it just needs the sync pulse to bring the trigger forward from a slightly longer natural period. Anyway in my usual style here are a few pictures. Top just showing EF91 Bottom of board, dead bug point to point style again. Anode showing approx 170 Volt saw-tooth from just under 200 Volts to approx 25 Volts DC. This is the g3 pin or suppressor pin. peak at 30 Volts going 100 Volts negative. Finally the screen grid, g2. A lovly point to take off any flyback suppression I would think, rising to a peak of 200 Volts and dipping to approx 75 Volts, sorry for the blurred pictures. I will add another EF91 to provide the see-saw opposite voltage. If I can find three scope probes I will try and take a shot with all three waveforms. The control grid, g1 is opposite the g2 grid from 0 to -4 Volts ish, I know I do not have 4 probes. Adrian |
3rd Nov 2020, 11:25 pm | #25 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
Two more pictures, my third probe is only a x1 so can only monitor the control grid set at 5 Volts per div all the others 50 Volts per div.
First pick here is from the top control grid, screen grid and suppressor grid. Then we have anode and screen grid The flyback is presently 20uS which is just a bit long, should be less than 9uS to be effective I believe, guessing it depends on the depth of discharge of the cap and anode load resistor, which could well change when more of the circuit is in place. Adrian |
4th Nov 2020, 6:33 pm | #26 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
I have done a little bit more today and added another EF91 stage for the See-saw output, Again a couple of pictures one of the test build and the waveforms on the scope. A bit bright.
Adrian Mods perhaps this thread should get moved to the Homebrew section as I think it will turn out more test and build now, but will leave up to you. |
5th Nov 2020, 5:56 pm | #27 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
Added another two EF91's to the test board, this time to try and get the components something near for the frame timebase.
I have also started putting the circuit into KiCad as it is easier to do it as I go along, also gives the the chance to post and be open to suggestions on the circuit and values. The Line sawtooth was approx 175 Volts pp the frame only around 80 Volts pp? I know that I am not supplying any sync into it so not sure what to really expect. Also took a HT current and got 9.4mA up to now at 225 Volts. TV timebase 01.pdf Adrian |
5th Nov 2020, 6:33 pm | #28 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: Ideas needed to build a new 'old TV'
Super set of waveforms, Adrian! Congratulations!
I like the linearity of the sweep itself. Very impressive. |
5th Nov 2020, 9:47 pm | #29 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,195
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Re: Ideas needed to build a new 'old TV'
Hi Adrian, note that the X & Y plates on ES tubes will normally have different sensitivities
(different distances from the cathode), so you do not need as much drive on one as the other. Neat layout Ed |
5th Nov 2020, 11:05 pm | #30 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
Hello Ed.
I have been wondering about the DG7-5, it has a deflection around 0.25mm/V in the Y deflection and 0.16mm/V in the X direction. If with some miracle I do get final voltages of 80 'frame' and 175 Volt 'line' peak-peak when being driven with sync pulses, I think I should get a maximum vertical raster of 40 mm(+-20mm) and 56 mm (+-28 mm) horizontal if my maths is correct driving both plates? So with an overall tube diameter at 70mm and assuming a 60mm visible diameter. I need to cover 48 mm x36 mm so it may just do that. Please correct me if I am wrong. I can still raise the HT volts a bit, other than that I will try and get a DG7-31 or DG7-32, would love to get a blue screen DB but do not see them. The DG7-36 at 2.5KV is a bit high EHT for present plans. Thanks for the kind words Kalee20. The next step is to add another couple of EF91's for Video amp and sync separator, then I will use another copper clad board for others sections. I had a bit of fun driving the HP scope to derive a raster. Adrian |
6th Nov 2020, 3:42 pm | #31 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
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Re: Ideas needed to build a new 'old TV'
Hi Adrian, that looks about right.
I sold some tubes a while ago, but I found the listing and I may have the following around still if I can locate them 4EP7, 4GP11 DG-36, DG7-362; if you are interested. These are older more robust types that may post Ed |
6th Nov 2020, 4:29 pm | #32 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
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Re: Ideas needed to build a new 'old TV'
Quote:
Congrats on your progress and I'm watching with great interest. I also enjoy using the hybrid point-to-point and dead bug construction method. Really handy to return a component to ground wherever you like. Keep it going, looking forward to the next installment!
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6th Nov 2020, 5:06 pm | #33 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
Hello Ed, in the CRT's I am struggling to find information on them only found the 4GP11, the rest II could not see on the frank.pocnet site, unless there are a few wrong digits?
Up to now I will stick with the DG7-5 as I have two of them, probably not the best tube to use as I would imagine it could be a bit dim with the low EHT. But until I start to drive a tube direct it will be hard to determine. Hello Al, I must admit I am a bit concerned about the line waveform, OK it is free running, but the flyback time is a bit long, but await testing sometime next week probably, just added a few more holes to the board for more valves. Adrian |
7th Nov 2020, 11:19 am | #34 |
Heptode
Join Date: Aug 2009
Location: Carshalton, Surrey, UK.
Posts: 735
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Re: Ideas needed to build a new 'old TV'
Hi,
that is very quick progress ! and having the waveforms as well is very useful... my progress is going to be much slower !
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Regards Peter B |
8th Nov 2020, 3:22 am | #35 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
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Re: Ideas needed to build a new 'old TV'
Hello Peter; It will not be long before I have a burn out and take a few days away from it.
Continuing with progress:- I have been playing with a simple sync separator today, struggling with the frame, but managing to get it locking on line, just! I am using the Hedghog II as a video source and feeding this through a simple transistor to provide an inverted signal with the sync pulses going positive, then though cap and a 4K7 resistor to a diode clamp on the input of the EF91 sync separator. Unfortunately the diode is not doing a great deal as the sync level is only scoping at 0.2 Volt and 0.8 Volt video. I did not build any gain into the stage being unsure what levels I should expect from a video detector? This is the present state of it all, starting to look messy. The transistor inverter stage at the top fed from the Hedghog. What I am not sure of is the line flyback, I have shortened it to the point where the pedestal signal would just be starting, this done by a reduction in the anode resistance, unfortunately this has a side effect of dropping the voltage swing on sweep it is now down to approx 130 Volts, if correct a direct result of reducing the resistance with the same grid swing. The following pictures show how it is lining up at present, they show without the pedestal first, then with. I have tried to look for timing information with an explanation of how long the flyback can be. I have seen something at sometime, but can not locate it when needed. I need the same information for the frame also I seem to have a 7ms flyback time and again unsure how this fits in. I know it is going to be a simple TV, but want to reduce errors where I can. Adrian |
8th Nov 2020, 6:26 pm | #36 |
Heptode
Join Date: Aug 2009
Location: Carshalton, Surrey, UK.
Posts: 735
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Re: Ideas needed to build a new 'old TV'
Hi,
at a guess I think you might need a bit more gain in the transistor stage. I would also consider using a 2 stage amplifier ( maybe with a higher voltage rating transistor in the second stage ) in case you get any spikes from the valve part of the circuitry.. it wouldn't be good if the spikes got into the Hedghog2 ! I also found some details of a USA made Pilot Television with a 3 inch crt... from 1948 https://www.antiqueradio.org/PilotTV-37.htm of course this is 525 line 60 hz and fm sound...
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Regards Peter B |
8th Nov 2020, 6:41 pm | #37 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,573
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Re: Ideas needed to build a new 'old TV'
There is one of those TV's on Ebay at present, low starting price but going up quickly. Not really for the UK market as it is listed on the .com site.
If you scan through Practical television on the world history site there are lots of builds, I am also awaiting a PT circuits book from Ebay to arrive, as it should save me some trawling. On this side I will do a bit more tonight as I need to make the frame timebase variable, it is not at present, so adding a POT and some high value resistors. I did find that the flyback time should be OK, I eventually found a 405 line waveform with timings and providing I can stay on or within 17uS on the flyback I should be OK for the start of video, blanking. I will also be taking the supply to 250 Volts DC and see what effect that has on the sweep. I doubt any spikes would get back to the hedghog, but I will keep it safe. this only temporary as I have not included a video gain stage yet. Trying to find a good explanation of the sync separator within the PT magazines. Adrian |
8th Nov 2020, 7:53 pm | #38 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Ideas needed to build a new 'old TV'
Basically once the video was stripped just leaving the sync pulses it was then split two ways, differentiation for line sync and integration for frame sync.
G.N. Patchett did a 4 volume series called Television Servicing, there was also a hardback version that comprised all 4 volumes, it's worth getting if you can find them or the hardback version, contains all the basic info, circuits and waveforms both drawn and oscilloscope. Lawrence. |
9th Nov 2020, 12:34 am | #39 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,573
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Re: Ideas needed to build a new 'old TV'
I was reading through the PT magazines as they started theory articles, and then for some reason I seem to be missing them, must re-read when not tired.
The previous schematic I posted has errors, so need to correct a few things and add the sync separator. That is for another day. I was having major difficulties getting the frame to lock, the timebase was very 'jittery'. It took time before I realised it was down to pickup from the line timebase. Adding a copper-clad board between the frame and line valves settled it enough for me to lock to the frame pulses even with low video input.. This picture is of the inverted video signal to the sync separator and the frame timebase output. So when doing the build I must use screening cans for the EF91's to minimize this pickup and hand capacitance I was also getting. Thankfully I have some. I am working from multiple PT articles, trying to pick sections that are relevant to the build I wish to achieve. It means I can not just copy the circuit but need to make changes as I go and that should mean I need to sit down and work things out for myself, that way I might just learn as I go. The sync separator uses the screen grid to provide the frame sync pulses and the anode output for the line pulses, the valve is not biasing correctly for me so I need to work out why and set a better bias point just above anode cut off. It may be because I have insufficient drive from the sync, not sure a this point. Add a few more copper boards as screening sections, add the video stage and see what happens next? It is all good fun, I think. Adrian |
9th Nov 2020, 8:15 pm | #40 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,573
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Re: Ideas needed to build a new 'old TV'
I have not done any more on the project today other than have a play. This post is really just for a bit of fun, it gives me a bit of faith that the project may actually work, or at least has a chance.
Driving the HP scope from the timebase's and the Z in the 1 volt pp output from the Hedghog. It also shows I needs to work more on the sync separator as the test card can upset it considerably. It was good to see the frame and line locking in action. Adrian |