Scratch Build – In Progress Valve Radio Conversion: Thermionic Logic - 26/01/14

Cheers guys. Just need to stop being lazy and finish it now.

 

Mod of the month nominee ! well deserved and well done. The project is looking really stunning now.

 

Well I never. My gast is well and truly flabbered!!!!

Thank you so much for the nomination. Have a smile on my face so wide my boss thought I had been slashed!

 

Got my vote

The only thing better than your radio conversion I've seen this year is a 50s TV conversion

I love seeing old things brought back to life

 

Thanks very much for your support guys. maybe now I can can convince Mrs Boo to let me buy a new motherboard and CPU to replace my dodgy AM3+ setup! Something black and gold would match in rather nicely...

 

There is a small aspect of my build that has had me stumped for a while now. The original radio had a magic eye valve to the left of the tuning dial. These tubes were a fantastic piece of kit, showing variations in signal strength by altering the shape of the output illumination.



My perfect scenario would have been to install an LED replica of the valve which indicated power and changed 'signal strength' with HDD activity or CPU load. This however is an unachievable dream as my electronics skills are extraordinarily basic.
The original valve was no longer operational and replacements are very difficult to get hold of as well having limited lifespans of around 1000 hours. Combine that with not having enough room to install the transformer and control circuitry necessary for the valve and its obvious that using an original item is not feasible.

I'd be happy enough with a static power light but want something a bit more interesting than a green LED.

You can see the round window where the magic eye should to the left of the tuning dial in the image below.



So do you guys have any suggestions for me as to what I could use?

 

ive seen some small keyring size plasma plates that you could possibly fit in behind that hole, you wouldnt see the whole plate and couldnt really control it by cpu usage or anything but it would give you that kind of effect

 

You could use Tachduino and control multiple LED's with it.

 

I was actually looking at a small plasma ball that I found on google but couldn't find a retailer. Not 100% sure it fits with the build though.

The problem there would be blending the individual LED's to look like the magic eye output. Could maybe use an acrylic tube with an opaque core to diffuse the light?

 

Actually, you can buy ready-made circuits that use a magic eye as CPU activity indicator:

http://www.elektor.com/magazines/2010/january/usb-magic-eye.1191254.lynkx

Control over USB (it is shown with a different type of magic eye, but any type works). Note how tiny the circuit is, which includes the transformer and is fed by USB power.

There is also a circuit diagram for a magic eye as HDD activity indicator:

http://homebrewing.com.pl/komp/KOMP_en.html

Here it is in action:



Magic eye tubes are not that hard to get hold of, and not expensive. EBay does a teeming trade. Some are brand new in the box --never used surplus stock.

 

Nexxo, that could be the answer. The valve my radio used was an EM11, of which few appear on ebay but as they are no longer being made they tend to be used and untested. Did see one or two new in box ones but they sold for nearly £100. There seem to be more of the EM84 type valves on the go, as used in the first circuit, but they are viewed from the side rather than from the top so would be of no use.

As this circuit would provide the perfect result though I think it would be worth spending the time trawling ebay to find a suitable valve (or three) to use with it. If the Russian 6E5C valve would work on that circuit then they are relatively inexpensive.

Thank you for that.

 

If you go with the first circuit, the top-view equivalent of the EM84 appears to be the 6E5S / 6E5G / 6G5G magic eye tubes. They go for about $15,--.

In principle every tube should work --their pin layout may just vary a bit, but that is easily worked around. All tubes come with a pin layout schematic. Just make sure you get something with a diameter reasonably close to the original.

 

PCB is designed for a 9-pin socket but 6E5 is a 6-pin valve so that wouldn't work. Need to find a 9-pin top view valve or get a custom PCB made (not in my current skill set).

 

Well, the kit is open source so you can download the PCB file. It could be modified in Eagle or software like that and then made to order. Heck, I etched PCB's myself, old skool in a tray of (mild) acid when I was a lad. I could give it a go when I get some time (which may be a little while). Pin layouts for the EM84 and the 6E5S substitute are both available on the web.

The rest of the components are off the shelf except for the pre-programmed microprocessor which can be ordered separately (but the program is again open source, if a forum member wanted to program one for you). The whole thing cannot take much to put together.

 

Wouldn't the circuit and programming need to be completely redesigned for the 6-pin setup? I am rubbish at electronics. Could solder it all together ok but circuit design is a mystery to me.

 

On the EM84 only seven pins are actually in use. Most will be just to feed power to the tube. There is only one that regulates the intensity/shape of the glow, and that is the only pin driven by the programming (marked GRID on the diagram below). So it doesn't matter which tube it drives, as long as the pin layout fits.

The 6E5S is an eight-pin tube with all pins in use, but there are conversion diagrams. Below is how you adapt an EM11 circuit (which is identical to the EM84 circuit except for the pin layout) to 6E5S for instance (don't worry of it does not make sense to you; it makes sense to me. ):



So it is not a difficult job to do. Change the order of the pin connections, add one resistor.

 

I would probably not mount the valve base directly to the board anyway so if I could just use the pins I need and disregard the others then that would be easiest.

 

You could buy a tube experiment socket PCB from eBay:



And then hook up the wires from the driver PCB in the desired positions. Easy.

 

Been looking into this circuit. I am struggling to find some of the components (I don't really understand what they are asking for) and cost of parts alone is looking at over £100 with shipping. My worry is that I get it all and it still doesn't work with the 6E5S as voltages may be subtly different.

....

...I'm scared!!! lol

 

The only part that is not off the shelf is the preprogrammed microchip. The rest could be bought in any electronics store. The tube voltages are all identical. The 6E5S has a different voltage on the grid, but the extra resistor compensates for that.

Of course £100,-- may be outside of your budget, so YMMV, but the circuit would be fine.