Now Radio Caroline has been back for some time on 648 KHz I want to build a very basic MF TRF receiver (preferably as much out of parts I have lying around), I think I've found where I can get suitable tuning capacitors (at least they are still sold) but I get stuck with how to calculate the dimensions of the tuning coil (especially if not using a ferrite rod) and what to use for a detector (will a modern Si transistor even work?)
I have looked at the thread on here but many of the circuits on the last post to be as old as I am and many seem to either use FETS which are becoming harder to find in discrete/through hole size (I avoid SMD for hobby stuff if possible) or germanium devices.
I know there are (somewhat overpriced) kits for kids sold at Amazon and such places, but I'd like to "roll my own" simply to keep my (basic) construction skills active, and also to show my younger friend who also helps volunteer at the local (FM) community radio station how the old stuff works..
Strangely enough, I was thinking earlier today (which is a dangerous occupation for a start!) about a homebrew 'electrics' tester that was built by a then Yorkshire Electricity Board, (would we call him a 'linesman' or an 'engineer'?) chap. Outwardly, just a modest sized wooden box with a few switches and gauges on the outside, and some small bulbs hidden within (visible through some small windows in the box). He used this thing for all manner of 'quick checks' from basic 'live/dead' line, to testing Earth Leakage Trip and a dozen other functions that I have long since forgot.
It even had basic self-test functions to ensure that it was itself working before and after testing live lines.
I do remember him demonstrating it on-site, here, on both single and three phase mains when we first moved in in 1984, and I do believe he was quite (and justifiably) proud of his gadget.
No doubt the Health & Safety bods would have plenty to say about it nowadays........ ?
Now Radio Caroline has been back for some time on 648 KHz I want to build a very basic MF TRF receiver (preferably as much out of parts I have lying around), I think I've found where I can get suitable tuning capacitors (at least they are still sold) but I get stuck with how to calculate the dimensions of the tuning coil (especially if not using a ferrite rod) and what to use for a detector (will a modern Si transistor even work?)
I would say regarding the coil - that's what Langford-Smith is for and as for the transistor detector, it's all a question of bias...
I've got several projects on the go, some digital conversion CRT sets, a neat little mains voltage indicator (the basic unit very cheap at about a quid), and some LED torches (I've been asked to make some more of my "BT2" Box Torches.)
With the digital conversion TV sets I'm looking to collaborate with some folk (and learn in the process), as I am comparitively new to the industry, although I've made myself completely aware of CRT dos and dont's before jumping in. With all three sets I'm having synchronisation issues, and with one of the units I'm having to re-create an input stage (PCW8512 monitor to composite conversion).
I'm fitting these projects alongside the music projects I and my wife are doing, as well as a busy church life, so these projects are not going to happen overnight.
The mains voltage meter was really an idea born out of a curiosity. Living in a remote farmhouse, the voltage goes down during the day to such an extent that the fluorescent light in the kitchen refuses to start. I'm interested in seeing what voltage the light eventually comes on at. It's an old Fitzgerald fitting with a 240V induction ballast.
Hopefully I'll have some pictures to show soon. The idea is to show one of the sets displaying footage of its own history and construction. Unfortunately I don't have a dedicated workshop space at present so it all presently happens on the kitchen table!
As to voltage and resistance standards - I used to work in a calibration laboratory, and was used to working with multi function calibrators made by Datron, Fluke, Time and Transmille. The highest grade voltage standards were the Fluke 7001 with 1.808V and 10V nominal outputs with recorded accuracies of a few ppm. These fixed outputs were used to periodically keep an eye on the 8 1/2 digit multimeters used as measurement standards. Noise, always an issue on mains powered kit, could be a problem, so there was a battery powered 10V standard by Cropico; it ran on a large number of D cell batteries that had to be periodically replaced, but was totally noise-free, although not as accurate as the Fluke 7001. The lab also had a full set of 4 wire resistor standards from 0.001 ohm to 10K ohm. Anyway I've digressed off topic!
Now the Ekco is complete bar another CRT, I'm restarting a monitor project with the MW6-2. Once underway I'll be opening up a thread.
Could you be making it into some kind of video projector? or are you going to make it direct view? I always thought that the projector tubes run at high voltages. I've had the thought myself of creating a large screen green monitor using a green CRT out of an old projection set. The 25KV is pretty scary on these things!
The raster is roughly the size and shape of a projection slide, so it may be possible to use the optics of a slide projector.
I've had the thought myself of creating a large screen green monitor using a green CRT out of an old projection set. The 25KV is pretty scary on these things!
The EHT supply is similar to the early CTV’s that required 25Kv, the CTV’s required around 1.2ma, the MW6-2 specification states to keep the current drawn below 200μa, if you can keep safe with a CTV of the 1960’s/70’s you should be ok with the MW6-2.
I never got to work on projection sets, I saw the pictures and thought they always had a dull look to them but understand when they were designed it was the only practical way for a large screen. They gave a picture of about/the same size as a 21inch CRT and those became available during the second half of the 1950’s.
An engineer I worked with said they had sold only one and a fault they had had a couple of times was the MW6-2 imploding, the glass was retained inside the optical unit.
So I would say you need to protect yourself from that occurance as well as standard high voltage safety procedures.
I've already had a picture of sorts with 5kv, I'm using a TDA1170 for field scan and it only draws milliamps for full height. Line scan again needs little power too at this low EHT. I'm going to try 7kv on the final anode and sort out the line scan then improve video drive
Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
If you are getting a picture with 5Kv it appears that 25Kv will not be required, that’s good because theses crt’s produce soft x-rays at that voltage and they don’t have the type of glass used in CTV Crt’s to stop the radiation, the optical unit contained the radiation.
That’s a good result, the frame is about right. Perhaps ready for its own thread.
Agreed.
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.
Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
The last thing I built was this to generate 405 line sync pulses. I can't say I'm very proud of designing with monostables and I'm certainly not proud of how it looks so it's hidden in a metal box.
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.
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'..!
Hi Marion.
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.
Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
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'.
