SR Flip Flop Display: Part 1 - Negative Voltage from Positive Voltage using a Hartley Oscillator 

My goal with this was to make it as close to completely hollow state as I could! The only thing I'm not a massive fan of are the fact that I used LEDs. I really want to remake this with some good VFDs for indicators instead!

@@UsagiElectric Pitty you don't have the power for Nixies, It could display 0 and 1. :)

@@UsagiElectric life really was so much harder before semiconductor devices became commonplace

@@frankowalker4662 He's just 2x MPSA42 transistors away from that. But wait.....THAT can be hollow stated as well!

Thank you for checking them out!

You know, now that I think about it, that was a pretty counter-intuitive way to tackle the problem, but it just so happened that I had some 33k ohm resistors next to me when I was testing it all out, so I gave those a shot, haha. I really need to figure out a good way to measure current, but I did do some testing with different resistors to see how the SR Flip Flop would react. Originally, I used 56k/56k with the -12V wall wart, then with the Hartley Oscillator, I used 56k/33k and we saw about -6V of bias. So, today, I tried 100k/56k and I saw about -8V and the circuit still worked excellently. Next was 100k/68k and measured -8.7V, and again it worked. I then tried 100k/100k and measured -10V of bias, but the multivibrator flip flop stopped functioning. I tried again with 220k/220k and the oscillator was providing -12V of bias, but the flip flop still didn't work. So, it seems that 100k/56k or 100k/68k is probably my best bet. At 100k/100k there isn't enough negative bias to balance it, and at 220k/220k there isn't enough power from the output of the opposing tube to keep the flip flop functioning. While this multivibrator is excellent, I have found that building NOR gates with two diodes and a 33k/22k/4.7k resistor network (i.postimg.cc/bYWcM5FH/Tube-NOR-nb.png) seems to be the most reliable and forgiving way to build logic circuits at 24V with these tubes. So, in the future, as we get into more and more complex circuits, I'll be using that design far more often. But for this display piece, I wanted to keep the design somewhat similar to the original flip flop design because I think that's a cool way to pay homage to the genesis of computing!

By running the heaters in series, I'm essentially doing exactly that! The heater is pretty much just a big dropper resistor, so if I have 24V and four 6.3V 300mA heaters, I can just string them in series and there will be a nice, 6V drop across each one. I could use a big dropper resistor for the heaters, and sometimes that's necessary depending on the circuit design, but the dropper resistor has to be a beefy one. Since I'm using 24V the dropper resistor would need to be about 60 ohms and able to drop at least 6W across it. That's going to generate a lot of heat, and if I'm generating heat, I may as well use that heat to move electrons in other tubes!

I believe that most switch mode power supplies don't tie the DC negative pin to mains earth, which means the positive and negative DC lines are technically floating. In this case, you totally can connect two power supplies in series. However, if the power supplies to connect the DC negative to mains earth, then you can't connect them in series as you would be essentially creating a short circuit across one of the supplies. The right way to do this is to inspect the power supply design and schematic and ensure that it's alright to connect up in series. The way I did it was to just send it and if I burned up a couple wall warts, well, they were cheap and that would have been fun too!

@@UsagiElectric thank you for the explanation 😁 really loving your series about vacume tubes, watching them all one by one currently. Your right, seeing them explode would also have been fun 😂

Thank you very much! I actually go into a lot more detail about electron flow and how negative and positive bias on the grid affects that in some of my previous episodes. In "The Triode Part 2.5" in particular, I talk a lot about how biasing the grid differently affects the behavior of the tube: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-C5WRS28FxUw.html In short though, essentially, when the heater heats the cathode up, a cloud of electrons that are thrown off the cathode form between the cathode and the grid. If the grid has a negative charge on it, that repels the electrons coming off the cathode. If the grid gets a positive charge, now the electrons are attracted to the strongest positive source inside the tube - the plate, which has +24V on it for the circuits we're building (the plate usually has 100V+ on it though, so the positive attraction is really strong). Now, how much grid negative bias is required to put the tube into cutoff and how much positive bias is required to push the tube into saturation differs pretty wildly from tube to tube. I did a massive amount of testing to check out the differences on the previous video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SUy5yNjTYnk.html Let me know if you have any more questions!

Thanks for the explanation! Will check out vid! 🙂

Thank you! I haven't yet actually, but that's primarily because I don't have any crystals in my collection. The Hartley Oscillator is surprisingly versatile and I can get really good sine waves out of them, so in most situations it seems to be a solid alternative to a crystal oscillator!

@@UsagiElectric Thanks for your reply. What about a generic 32.768 kHz watch crystal? There are also some vintage tube-like models around with the frequencies in the kHz range. Alternatively, you can consider the microcontroller oscillator crystals. Yet these are well above 1 MHz...

@@zygmunt418 No problem! Honestly, I don't do hardly any audio related stuff, so needing a crystal oscillator hasn't ever really come up. Though, I would like to build an AM transmitter one day because I live so far out in the middle of nowhere, we don't actually get any AM stations to listen to on the old tube radios I do have. I think for the AM frequency band though, I need quite fast oscillations, like 1MHz. That's a project for the far future though!

Thank you so much! And thanks for the kind words on the quality! It's kind of wild to think that we're going to some pretty insane lengths to build a single flip flop powered from a single voltage source when you can get something like a 74LS173 and get four D Flip Flops in 16-pin DIP package. And even more wild when you realize that the 7400 series of chips are now 40 year old technology! But, it sure is fun playing with tubes, so I'm gonna keep plugging away at it! I have a few ideas of how to tackle the heaters, so we'll explore those in the next episode and then clean the mess of wires up so we have something cool to set on the desk (and if there's time, I'll cut a circuit board for it and make it a proper display piece). For multiplying a single supply, if you can make an oscillator, a lot of options open up. I actually explored using the multivibrator to boost voltage up to about 75V to ignite a neon bulb, and while I got it to work, it didn't work well. But that was with the weird multivibrator oscillator, I've been meaning to try again with the Hartley Oscillator to see if I can get it working better. Perhaps a topic for a future episode! You know, while I was editing this video up, I noticed that the red LED was a little too dim, but it was a bit too late to fix it. In the next episode we'll definitely have something that's brighter and easier to see!

@@UsagiElectric I'm watching these from the latest towards to newest, so I do not know what you came up. I had two ideas: 1. get a wallwart that has a midwinding outlet of +6V. 2. Wire the three tubes in series and drop the excess 6V by a resistor or a lightbulb that can light your logo.

...which never prevented it from being the most common one - by far. Guess whether ANY of your tube TV powered up at all if your CRT filament kicked the bucket. And yes, shorting it out DID allow one to at least LISTEN to a TV show on the zombie set.