วีดีโอ

It all depends on what you can find in your area I guess? As-per the video, I am currently listening to a set with a VR137 in it and that works really well, BUT it might be difficult to find one, then you have to find the non-standard base to go with it. My preferred choice must therefore be either the 'ACORN' triode, the 955 or the identical valve in a different larger glass case, namely the JRC9003. There are LOTS of ACORN 955 triodes out there so I'd look for this. Note that there ARE bases for ACORN valves (even though I don't have any here) but I personally wouldn't like to use one as you have to force the little pins down into some strong metal clips... I think they might break... Use my own idea of twisted wire on the valve pins soldered to a piece of veroboard. See my picture in the video to see how this is done. Good luck with making it! Ps Just looked on fleabay here in the UK and found 15 of the 955 ACORN triode currently for sale.

Glad you found the idea useful! I might well try making a short video to give some more details on exactly how this is done. Thanks for the suggestion.

Ah yes. The 'SEX' instruction.... I thought that I might just miss that out for the video :-)

As this project was using the 'universal chassis' we use for several of our projects, the meter is simply there to show us the anode current drawn by the valve or valves. A x10 shunt resistor is used as well, thereby making the meter read from 0 - 10mA rather than 0 - 1mA. In the case of this circuit, you can see that the approximate anode current drawn for both halves of the valve is 2mA. It is also interesting to see how the anode current changes in circuits such as some regenative radios as well as the thyratron oscillator and is actually needed to see the crystal tester working properly.

@ thanks!

Thanx Clare! :-)

Pls. see my reply to your other comments.

All very true David. Indeed it is possible to run valves / vacuum tubes at such low voltages, not necessarily those destined for car radios either. Take a look at the small 2 valve portable short wave set I had published in Practical Wireless, I have also made a YT video of. This uses two 1T4 battery valves and use an 18 volt HT. You might also note that the 'universal chassis' I am using for the experiements, such as the one valve FM radio, double valve short wave radio, thyratron tester etc. etc. are all probably meant for an HT of +250 or +300 volts. However, I have deliberately set the HT on the chassis to a maximum of +90 volts. (As-per the original write up on it) IMHO, this issue about safety is always a difficult one to address. Some people are naturally clumsy and careless with these high voltages, whereas the vast majority are probably not. So aside from offering multiple safety warnings (that may well be ignored by the minority) I don't think there is a lot more one can do, aside from somehow banning everyone from using anything above, say, 12 volts? I recently saw a video on a TH-cam channel explaining how to take an old microwave transformer (circa 2,000 Volts on the secondary) and make burning patterns on a piece of wood with a saline solution. Absolutely LETHAL! I would go absolutely nowhere near it myself.....

Thanx Clare. Considering how simple it is, it's surprising just how well it actually works!

Thanks for the info. Ian. Whilst there are a surprising number of R1155 receivers remaining, very few can be seen still operating with their RDF circuitry.

The loudspeaker used for the test was a small cylindrical cabinet device made by Ariston, called an MSX-03 Micro-monitor. This speaker is actually in use on a daily basis connected to my 1 valve FM tuner, (which uses an additional ECL80 triode pentode to drive the speaker.)

It's really interesting to hear your story about your 1802. Yes, I can definitely see why so many people still like it. Of course in reality, it's somewhat strange architecture was ideally suited for beginners to 'cut their teeth' on, like the really simple but useful DMA access and of course that solitary 'Q' output line. I'm sure that I will return to mine (my three CPUs all work!) to have another 'play' in the near future :-)

@@lishaton Do not hesitate if you can get your hands on a CDP1861 graphics chip. It's very hard to find these days, but all old versions of the Elf used to have one. Simple black and white graphics by adding a single IC to 100 Dollar computer. Ar a time when computers still had no graphics at all. THAT was the Elf feeling. Always building and exploring, never routine.

I shouldn't think there are many of those left today! I actually have a stash of Motorola 6845's display controllers, but have never actually made one of them work as there is so much involved in doing so. Also, as CRT monitors are becoming thin on the ground, it's not exactly encouraging to do so from this department either.

I'm sure it will go well for you Rob. Hopefully you'll be able to check out the video to see how well the valve/tube of your choice should work :-)

@@lishaton Hello Sir, I am still busy tinkering with tubes like EF80 EL95 and QQE03/12 - Of course as a HF amplifier for the FM band BUT I will definitely make an FM receiver!

Thanks for the positive feedback! Your comments make a lot of sense. Although the 1802 is so very different to all of the CPUs I've worked within the past, by the end of the video I began to rather like it - if you read between the lines in my video :-) The basic DMA functions certainly do make it ideal for instructional computers such as the 'Elf'. Whilst you mention the relaxed clock requirements for the 1802, the Z80 is arguably exactly the same, in as much as you can do what you like with it, stop it start it, add another pulse etc. etc. and it doesn't care! Seriously useful if you're a beginner and want to investigate fully what is happening. See my first video on the Z80 if you haven't already. Cheers!

Thanks Clare for the positive feedback :-) Of course your NS SCAMP had much the same I/O facilities to the Cosmac 'Elf'. Lots of switches etc. to enter data and run the thing. Doing it this 'primitive' way, certainly made one realise exactly what is going on inside a computer. Z8001 then next??

Рад, что вам понравилось!

You're welcome! Interesting to hear that your own experiences are much the same as my own. Sometimes it's having those samples programs that give us a clue as to how one is supposed to work with them.

There's apparently still quite a following for the 'Elf' :-)

Interesting question! Certainly if one was going to use it on a 'high' voltage, like one does with a neon bulb for example, one would definitely use a current limiting resistor. However, in the case shown here where the device is running at this low voltage level, then I don't think it is necessary. When building up this circuit, I had no idea what 'HT' to use for the display, although I knew it was very low, so started off by connecting it up to a 0-20V PSU. Using this, I was able to slowly ramp it up and note when the display fluorescent anode started to glow. Around 9 volts if I recall correctly. Taking it slowly up to about 20 volts, (the max . for the PSU) then it was about the same brightness as one would see on one of these displays in normal use. Hence, I don't think at these voltages a limiting resistor is necessary and therefore didn't use any for the demo. you've seen. Hope this helps!

@@lishaton I've seen circuits where sometimes they are used and sometimes not which is why I ask. I think in most cases, the current draw of the anodes/grids is low enough such that resistors are not needed. I suppose one could measure the current to be sure. I've seen 10k resistors being used when driven by NPN, but that is because it is a common collector configuration. Thank you for responding.

Absolutely right! Apologies for that! One just becomes used to there being an A0 with an 8 bit CPU.

Sadly in the last couple of years, the last few big LW transmitters have closed down :-( As of October 2024, in the UK there is just BBC Radio 4 long wave left. I understand that at the moment, there are a couple of others (out of range from here in the UK) include Mongolia, Iceland and Romania. There may be a couple more out there too!

Good question! As our Paraset is only ever effectively used for 'demo' purposes with a low 150-180V HT, we've had no issues in that department. However, if you were to use it with a full whack of 250 - 300V, then I would personally only use air spaced caps.

Thanks Clare - again!

Всегда пожалуйста!

Ah! You found it! It's actually quite a complex bit of circuitry too.

Thanks Felix!

Thank you Clare!

Thanx Clare! busy expanding the thing at the moment!!

Hi John, for your future reference: radarroom.125mb.com/html/contact.html I remember visiting Salisbury Hall in the early days when you only had the prototype Mosquito and you allowed people to go up in the cockpit. (Somebody said recently that you now do this again?) Sadly we don't have a musum as such that one can visit, but we have had one-off visits to view equipment in the past. Please contact me direct and we can find out whether we can help you with more detailed pix or a better video etc. Chris

Thanks for the positive comments.

You have a couple of interesting VHF transistor receivers on your site.

Extremely unlikely methinks... :-)

Interesting tale. When the EE8 set worked for me, it was always a bit internittent because of the horrible springs used for the connections. One always had to bang it a few times to see if that made it burst into life... I think it's fair to say that I didn't manage to make several of the projects work either. Yes, the transistors could well have been vapourised. I have to admit that although I built the radio set, many times over, I hadn't a clue about the circuit diagram and I had no idea how each bit worked either.. A year or two after the demise of the set (in 1966 to be exact), I was given a copy of "The Beginners Guide to Radio" by Newnes books. I still have it in front of me as I type this! The first set I built from this was a one valve radio and it worked! Hence it became the first radio that I'd built outside of a kit. At last I really began to understand a few things!

Most interesting. I hadn't heard of that being done before. These receivers were very popular here in the UK after the war and there still seem to be a lot of them around today. I've always been impressed with the high quality of construction from the US with their equipment, plus the superb maintenance manuals - IF you can find one!

@@lishaton Sadly, I've never owned an American receiver of that era: I was always jealous of my friend's National HRO (so much better than my clapped out British R107 and PCR). Most US sets were masterpieces of precision engineering, especially the tuning mechanisms. ♥

Most interesting observations. All points notes and quite valid. I tend to start using it with the smallest noticeable movement on the meter, then slowly increase this to give a better accuracy until one reaches the setting at which the issue with the frequency suddenly 'snapping' as you say, manifests itself. Back off slightly from this setting and take the reading. Thanks for the feedback!

@@lishaton I think that maybe one way to prevent the undesirable frequency pulling is to add a buffer amplifier after the oscillator, and to connect the output of the buffer amplifier to an untuned coupling loop, which then goes through a diode and through a microammeter to ground. The buffer amplifier will drive the oscillator's output through the coupling loop, through the diode, through the meter, to ground, creating a current readout on the meter. Then, if an LC tank is brought near the coupling coil, it will suck out energy from the buffer amplifier (not directly from the oscillator's LC tank itself), causing less current to flow through the diode and the meter, thus showing a dip. This approach should prevent frequency pulling of the oscillator because the oscillator's LC tank is never coupled to directly; we only couple to the coupling loop on the buffer amplifier. I've seen a similar approach recommended in some articles, and I think the MFJ dip meter also uses this approach. I haven't had a chance to try it myself yet.

If you ever try an example, do let me know how well it worked.

Thank you! :-)

Thank YOU Clare!

Ah! The ARC-5 R28.. Quite an amazing bit of kit to see actually working properly with all its electro mechanical bits :-) I have a second one of these I must try and fix one day, plus the matching VHF transmitter....

It sounds as if your kit was really worth the money paid for it then. I'm afraid that my own EE8 / A20 died many years ago and I'm not sure if anything survived from it. The 'photosI used in the video were from all over the Internet to show what it used to look like. The actual circuits I used for the video, were exact copies from the original 'cards' that were supplied with the EE8. I was given the A20 add-on kit a bit later on which gave two loudspeakers, a third transistor, a few more bits and many more circuit cards. I made the radio and the intercom many times from this!

Thanks Clare! Though I'm sure it could be improved upon with a little work :-)

I think that I was about the same age as yourself when I received mine :-) You are quite right about the AM radio today. Here in the UK, there are very few 'National' type transmissions left. When I built my radio from the kit, it worked really well as we were reasonably close to a main BBC transmitter. You'll no doubt have noticed that for my demo. in the video, I had to use an external aerial AND an earth to make it loud enough to hear it working. At time of writing (April 2024) the BBC, our National broadcaster, is in the throws of permanently closing down our large Long Wave transmitter, which is such a shame, as there are many who live miles from any other transmitter yet can still receive Radio 4 on Long Wave - 198KHz.

Yes, it's surprising just how many useful measuring tasks one can do with a simple bit of circuitry like this!

.

Еще раз спасибо :-)

Thanks Clare! Hopefully someone will find it worth making..

Somente em código de máquina Z80. Você quer dizer para o 8051?

I agree. The whole philosophy behind the 'Radar Room' being to make things actually work, even if that means using artificially created data sources for items such as GEE, Loran and Chain Home, as they are no longer transmitted over the ether.

A good question! In keeping with all my own micro' work, I wrote this in machine code. (I always do things the hard way!) The idea behind using this technique for my videos is to keep things as simple as possible. I remember when I started writing my first few lines of code, I didn't own a computer at that point and knew nothing of assemblers either. For this reason you can see why machine code was the only way forward for me. Obviously for a beginners perspective today, using an assembler must be the logical way forward, as everyone must at least have access to a computer. As far as compiling from C++ is concerned, according to a quickie Google search, there are plenty of them out there that will. Do check this out yourself and see if any suit your purposes. It goes without saying, that there are many assemblers for the 6502 if that's your choice in the end.

Спасибо за ваш интерес!

Positive comment appreciated :-) Thanks!