EEVblog #833 - Mailbag

[EEVblog]

Christmas Mailbag!
Warning:
Someone thinks atheist Dave won't get saved by Jesus, so tries to convert him to Christianity!



SPOILERS:
Tandy PC-6 Pocket Computer
Service Manual: http://www.pisi.com.pl/piotr433/manuals/pc6sm.pdf

Silego GreenPAK4 Mixed Signal Development Kit:
http://www.silego.com/buy/index.php?main_page=product_info&cPath=58&products_id=388

Isolated USB to RS422/RS485 converter board. The isoUSBRS422
http://www.alperyazar.com/projects/isousbrs422/v1/home
Vintage components
Airbag system car occupant sensor.
An audiophool valve Hi-Fi headphone amplifier

[pickle9000]

Awesome ending (last 10 minutesish), totally laughed my gut's out.

[Felicitus]

At 9:41, the device in the image shown is a Korg Electribe SX-1, which uses tubes for a richer sound. Tubes have a "warmer" distortion than regular distortion circuits when driven into saturation. This is no audiophoolery, but actually a widespread technique and well-documented. Beginners should read the Wikipedia article.

[Muttley Snickers]

Another great mailbag and a good variety of some very useful devices......

Wishing everybody all the best, we have had some good times this year......

I think I ate way too much......

[rrinker]

Never had the PC-8, but I did have a PC-4. The neatest thing I did with it was to make a launch controller for model rockets. The supplied launch controller used like 4x AA batteries and had like a 3 meter wire. We used to take turns launching, because it looked much cooler standing further back. Plus the AA batteries were good for maybe a half dozen launches. I had the PC-4 plus the cassette interface, which had a relay for controlling the tape motor. I took a large project box (all from Radio Shack, in those days) and put in two holders for D cell batteries, four in series and the the two groups in parallel, and added a hefty relay with a protection diode across the coil. Two safety switches, one shut off power to the rocket and the other cut off the tape control from the PC-4 to the relay. I wrote a simple countdown program so we could set up a rocket, start the program, and then both stand well off and watch the launch. Great fun. Probably my first 'use a computer to control something in the external world' project.
 My favorite was probably the miniature pen plotter they had for the PC-1. An actual 4 color pen plotter, not a thermal or impact dot matrix printer. Amazing miniaturization by Sharp.

[vk3yedotcom]

That valve was a 6J9.

Here's slightly longer teardown by a keen EEV viewer



"as the Aussie bloke says 'we're in like Flynn'!"

As if the heater glow wasn't enough, note the cringeworthy use of LEDs used to give artificial lighting.

I've had good results using 12 volts plate voltage even conventional valves like the 12AX7 but audio output is low and requires something like an LM386 to amplifier.

[Pentium100]

I really dislike the blue light on the tubes, unless it's the fluorescence on the glass, in which case I like it. The tube glows by itself, there is not need to stick a LED under it.

Also, there are some low voltage tubes, primarily made for car radios, I do not have any though. I do have some low power tubes intended to be used in battery powered radios (heater - 2V 60mA), though they need ~100V anode voltage. I may at some point do a portable headphone amp or something with them, once I have built all the "normal" amps that I need .

I hope Dave does some "Fundamentals" videos on tubes - his explanations are much easier to understand than the text books.

[Stonent]

I really dislike the blue light on the tubes, unless it's the fluorescence on the glass, in which case I like it. The tube glows by itself, there is not need to stick a LED under it.

Also, there are some low voltage tubes, primarily made for car radios, I do not have any though. I do have some low power tubes intended to be used in battery powered radios (heater - 2V 60mA), though they need ~100V anode voltage. I may at some point do a portable headphone amp or something with them, once I have built all the "normal" amps that I need .

I hope Dave does some "Fundamentals" videos on tubes - his explanations are much easier to understand than the text books.

Maybe it's using Cherenkov Radiation?

https://en.wikipedia.org/wiki/Cherenkov_radiation

[coppice]

The car seat occupant sensors I've seen are simple switches connected to one of the seat springs. Those stprings stretch so much that very positive reliable switch operation is trivial to implement.

[Pentium100]

Maybe it's using Cherenkov Radiation?

Actually, some power tubes (for example 6AS7G or 6L6G) have a very faint blue glow. It is caused by some electrons missing the plate and striking the glass. There is also a blue glow on the inside of the plate, but it usually only visible when the cathode has not fully warmed up because the orange light from the hot cathode is much stronger than the blue glow.

[boffin]

From the 22nd second I knew this was going to be a good one.

Have a great festive season Dave.

[rollatorwieltje]

Those pseudo tube amplifiers always amuse me. So much trouble just to use a shitty generic valve, and then they use 2 jellybean opamps as output stage... Not to mention the hv switchmode psu close to the audio path.

Wonder if I could use this big boy for a headphone amplifier

[george graves]

I don't know jack about tubes.  Wouldn't mind a DJ rant/video about them.  The whole "Christianity" thing was cringe worthy.  Yikes.  Even as a Christian I was yelling at the screen "Please don't - please don't - it's Dave, he's just going to make fun of you - he lives for this kind of thing - it makes him happy inside!  You're making his day right now!"

[Salas]

I don't know jack about tubes.  Wouldn't mind a DJ rant/video about them.  The whole "Christianity" thing was cringe worthy.  Yikes.  Even as a Christian I was yelling at the screen "Please don't - please don't - it's Dave, he's just going to make fun of you - he lives for this kind of thing - it makes him happy inside!  You're making his day right now!"

Truth is the wandering ... the game of the world. Technique and reason are just newer myths to end previous myths, all are facets of the game. Players and the game making dents one to the other. Humanity is just the talking part of the cosmic game. Nothing is ever conclusive, the future is unwritten. Humans are not fundamentally reasonable beings as a living part of the cosmos for a... reason. The reason is that nothing will ever appear conclusively structured because it is what it is whenever it manifests randomly. So lets not sweat it, when reason makes some people cruel or myth makes some other people cruel its just what they should not be following. Play fair and enjoy. Games are for fun. Merry Christmas to all.

[HKJ]

The flashlight is not gold, but copper and the sealed bag is to keep the copper pristine until you get it. The two leds is probably because they sell two versions of it one cool white, the other warm white.

[c4757p]

Truth is the wandering ... the game of the world. Technique and reason are just newer myths to end previous myths, all are facets of the game. Players and the game making dents one to the other. Humanity is just the talking part of the cosmic game. Nothing is ever conclusive, the future is unwritten. Humans are not fundamentally reasonable beings as a living part of the cosmos for a... reason. The reason is that nothing will ever appear conclusively structured because it is what it is whenever it manifests randomly.

<img src="wat.jpg"/>

[janoc]

Dave, the card reader is not a SIM card reader but most likely an authentication device. You stick your debit/credit card in it and then the bank's internet banking uses it for challenge/response authentication of login or any other transactions you do. Or even for cryptographic signing. These are quite common with EU banks.

[vlad777]

Dave, I invite you to believe that tubes are cool. Even though these days they are mostly connected to audiophools.
I would like to see a video ,like fundamentals friday, where you explain a little bit of theory of operation and build and
probe simple circuit with a tube.  So I don't have to do it, because I am under impression that you need various and high
voltages for valve circuits , which means buying or winding a transformer.
So simplest explanatory circuit ,with a tube ,connected together and probed would be nice and useful to watch.

[tchicago]

Hey, Dave, Merry Christmas!

I'm an atheist too, and I do enjoy Christmas. It is a colorful and happy time of the year, so I take best from it. And I do hate those atheist activists who go around and file lawsuites against the stores and malls that put out the Christmas decorations or say "Merry Christmas".
Besides Christmas I also enjoy many other elaborate fiction stories. Star Wars, especially when the new episode comes out, and I celebrate that too.
Same about James Bond. I also like Battlestar Galactica, Futurama and American Horror Story. I'm not a big fan of Star Trek, but the recent remakes are pretty enjoyable. I totally don't understand Lord of Rings. But I'm definitely not going to go out and make fun of Star Treck or LotR fans, as they take it rather seriously.

There are many fictions stories around, and I like many of them and I also like the certain aspects of some of the rest. But it does not much make sense to take to much fuss about those stories I don't like.

Christmas = lots of lights, LEDs, DC-DCs, PWM, sequencing, fun!

[Pentium100]

So I don't have to do it, because I am under impression that you need various and high
voltages for valve circuits , which means buying or winding a transformer.

Most of the time you need a low voltage (usually 6.3V) high current power supply for the heaters (can be AC or DC) and a high voltage (200-400V usually) low current supply for the plates (DC only). If getting a proper 220V/220V or similar transformer is difficult you can always connect two similar transformers back to back (say, 220V -> 12V -> 220V) to get the plate supply. Some tubes are designed for higher voltages and low currents, some are made for lower voltages and higher currents. For example, an ECC88 can be used quite well at 60V or so.

[vk3yedotcom]

So I don't have to do it, because I am under impression that you need various and high
voltages for valve circuits , which means buying or winding a transformer.

Not always.

6.3 volts is easy to generate from a 12 volt DC supply and an LM317 regulator or similar.   Or you could use a valve like a 12AX7 with the two filaments in series (use the right connections otherwise you will blow it!) or 2 x 6.3 volt valves in series so no regulator is needed. Excessive voltage reduces lifespan so aim for as close to 6.3 or 12.6v as possible.  Maybe two series dropping diodes if your power source is 13.8v DC? 

As for HT you could just use the same 12v DC (in some cases), several 9 volt batteries (3 will give 27v) or experiment with DC-DC converters.  The current required for experiments will be just a few mA.

[Artlav]

Merry Incoming, everyone.

Oddly enough, it took me until a few months ago to realize Christmas was actually a religious holiday in the western world.
Here we celebrate New Year, and it looks exactly like Christmas with a different colour scheme.
But below the superficial it's two completely different holidays - New Year is secular and don't have a trace of religion in it other than the calendar itself.
So, it's literally merry for everyone, with no fear of offense.

P.S. Nope, these tubes aren't genuine Russian ones. Not even close.

[tszaboo]

Dave, I wish you Happy Holidays. I'll tell you the truth. I'm an atheist, just like you.
But, every now and then, I'm being asked about my religion, I prepare to the worst. People don't ask questions about that, unless they are from far away, cultural difference, they are just curious. I'm talking about the other question.
Saying, that you don't believe is the bad answer. Saying, that you know, there isn't one deity is a wrong answer. Because then there is a bullseye on you, you are a free target, someone who can be converted. Conversation goes badly, because they believe, and you need to give facts, and proove stuff.https://en.wikipedia.org/wiki/Russell%27s_teapot
So every time that question is asked, I answer:
Yes, I believe in the Flying Spaghetti Monster.
No burden of proof, no trying to convert. You get to make fool of them, using their own rules.

[Brumby]

If nobody has put their hand up for the headphone amp, I will.

[Muttley Snickers]

If nobody has put their hand up for the headphone amp, I will.

A trap for all players, the conditions stipulated first comment (Youtube) not first post (Forum), I fell for it as well and got beaten by an hour.