Does anyone want to build anything these days?
That’s a good result, the frame is about right. Perhaps ready for its own thread.
It's just a little fun project with mixed technologies. Got some novel ideas up my sleeve for a video amp and line generation. Incidentally I'm using an LM1881 for synchronization.
I'll start a new thread soon.
Posted By: Peterscott
I'm just looking at the circuit and seeing some similarities with the PCW monitor mod I'm attempting. The set contains the very same 74LS00 chip. Other than that the set contains standard off-the-shelf Television chips. My aim is to feed a composite or S-Video mono signal into the monitor board from a digital converter such as a Roku or Freeview digibox, but I need to supply sync signals to the two time base signals as well as a true analogue signal to the cathode transistor on the neckboard. My initial thought was to bypass the 74LS00 and feed the monitor at two places using either a proprietary video amplifier, as the horizontal and vertical ICs both have sync separator inputs, The good thing about the PCW monitor is that it has some good DC sources at 5, 12 and 24 volts dc to power ancillary circuits and the cabinet is spacious enough without its original processor board to accommodate audio and a couple of digital converters. Maybe we can repurpose the IC to do what your circuit is doing. PCW circuit diagram is located in the library, so I'm told, so no need to post it here. Of course I will require sync pulses at 15.625 kHz for 625 lines. I'm a bit rusty on these old TTL circuits and how they link directly into the analogue circuitry of the sets.
Any help would be appreciated!
This is one of the initial experiments, TDA1170 frame drive, 2vP-P sine wave line drive from phone oscillator!!! and 3v P-P video drive.
Good heavens, Trevor, that's the first time I've ever seen a perfectly folded 'test-card tee shirt'..!
It takes a lot of patience I can assure you.
The intersting thing about that little test was how little drive I needed to give me a scan of sorts, I was using the 3.5mm headphone socket on my smartphone, with the oscillator set to 10,125Khz and sine wave, I was surprised it worked at all 🤓 Adjusting the volume was the width control. I have been toying over the idea of seeing if the TDA1170 will work at line frequencies if so that would be an extremely neat solution, the only problem could be flyback but I may give it a go.
I've now completed the mains monitor and it works very well!
It has become quite a revelation how much our mains supply varies throughout the day. Obviously this will be a factor when restoring old TVs in the future. The lowest observed voltage was 219 and the highest sio far has been 247V. Obviously out here we only have a singke-feed 11kV to the farm site which feeds a 240V transformer on a pole. Being a bit far away from civilisation there is no gas, so all cooking is done electrically. I don't know what effect this would have on older tellies such as Thorn 1500 with resistor-fed power supplies? I guess the valves and CRT heaters will glow a little brighter at 247V, and the picture will baloon a bit. My first project sets are being fed from switch mode wall warts and shouldn't be affected.
I've also found a neat solution for the Zenith chassis monitor based TV, parts are on order. I thought about a solution for quite some time on how to modify this to accept composite video. It turns out that the video signal for this monitor is analogue video with TTL horizontal and vertical synchronising signals. The best approach was to provide a synch separator in the form of the LM1881, which along with a couple of passive components will be mounted on a separate veroboard that will be mounted on the inside of the chassis. I have been advised that the signals should be ok to go straight into the edge connector of this 1984 chassis. When I have something up and running I'll search out the project's original post and add some pics as it progresses. I want it to look retro but be able to receive modern digital signals either through IPTV (via wi-fi) or Freeview, with possible DVR functions so I can play classic telly from memory sticks. There are some other issues to deal with when using multiple digital converters. It would appear that the Roku's composite TRRRS jack socket only outputs at NTSC 525/60, whilst the Freeview gives you a standard UK 625 line PAL signal from its phono or scart socket. This might be solved by using an HDMI to PAL standards converter instead of using the jack socket on the Roku. Dual Standard in 2018? I sort of see what the TV manufacturers had to go to when we had 405 and 625 side-by-side! It made for extra complication! Thankfully, being mono, I've not got to worry about colour(PAL and NTSC)!
Occasionally had this problem but I only had the odd one or two places were this occurred.
The LO in the tuner was usually the first to fail, working ok after the cooker was switched off. The HT would be down a bit but the slightly smaller picture didn’t seem to concern them as long as there was a picture. These sets has silicon HT rectifiers, a valve rectifier would probably need changing early as well.
The mains voltage at my house is very consistent, usually between 249 and 252v, right at the upper end of the 10% tolerance.
Something I'm playing with is a wide band envelope detector and a log amp.
It's interesting investigating various sorts of detectors, the theory behind them and their strengths and weakness and knocking together prototypes to see how well they work. However, building a circuit which works from 100KHz to 50MHz isn't a job for Veroboard.
Then there are chips available from TI, AD and others which perform these functions to a very high spec and only cost a few quid. Then there are ready built modules from China, which cost little more than the chips. I think I'll end up using the Chinese modules.
Hobby electronics as a widespread pursuit seemed to fizzle out in the mid 90s. That was when Maplin seemed to move away from it and the several magazines disappeared from the newsagents' shelves. I think there were a number of reasons. Back in the day a valve radio was expensive, but the technology was accessible and they could be repaired with some knowledge and next to nothing in the way of test equipment. In the 60s and 70s people were building things like darkroom exposure meters and electric organs. Now you can buy almost any gadget you want very cheaply, but the technology is nothing like as accessible. Hardly anyone will be building electric organs these days. Then there's the second hand market. In the 70s and 80s there were a few frequency counter projects in the magazines. Now you can buy a used Racal, with an overnised crystal and much better performance, for less than £30 without trying very hard.
I've got a couple of bound volumes of a magazine called Amateur Work from about 1900. There are several lots of plans for American organs, fretwork projects, electrical projects, metalwork projects and endless discussions about soldering, soldering irons and fluxes. I think there have always been people wanting to tinker and make things. Amateur Work was one way in which it found expression. Hobby electronics in the 60s, 70s and 80s was another - although it began earlier. I'd say these days it was Arduinos, robotics, Raspberry Pi's and 'making'.
Just about everything has been shelved since early January with my wife falling ill very quickly and then passing away on the 26th of January. I had lots of planned ideas and projects before Christmas and was looking forward to this year. It of course has been terrible so far and I as yet have not got my head around the events so far.
I know that I need to come terms with it all as my own health is not what it was and already I have lost weight and feel quite lost. The hobby and my like minded friends could well be my saviour and I hope to visit some this year God and health permitting. I'd like to try and be more positive, I'll never forget Anne nor would I want to but I know she would want me to resume things I used to enjoy.
On a positive note I opened up the shed yesterday and gave it a good tidy, I did get a little comfort doing that so I really do hope that given time I'll back to enjoying my hobby one more and do some projects.
Sorry for going on a bit, it is though good therapy to just write down how you feel in this situation.
 Sorry for going on a bit,  it is though good therapy to just write down how you feel in this situation.
 Never think that Trevor and  you're absolutely right, so please express yourself however and whenever you wish. We're all here for you and will help you to take those slow steps towards healing. 👍