How to build a Portable valve radio?

[Matthias Gladstone]

Evening all,

One of the things I want to build for Lincoln, and as a summer project in general, is some form of portable radio. The general criteria are:

• Must be portable (battery powered)
• Must be fairly simple to build (electronics wise)
• Would be nice of it used thermionic valves somewhere
• Range of channels is not an issue, as long as it picks up some signal or another

The basic idea is to have it as the backpack which supports my two samurai/pirate back banners.
I'm not completely inexperienced with electronics - i've just sat an engineering module in it - but i'm a bloody long way from an expert, and to be honest, I don't really know where to start.
Having said that, my rough idea so far is to use a crystal radio as a base, possible cheating with modern electronics (Transistor?) in the tuning, then using a simple valve-amplifier to amplify the signal and send it through the speakers.
Does anyone have any thoughts or ideas that might help? Ideally, i'd like to have an original design, rather than standard maplins kit sort of job, even if that does mean copying and melding together circuits from other radios.
Is it true that valves need a seperate high-volate circuit to operate? If so, I do have a small lead-acid battery I could step up, if the current could be made to alternate somehow.
cheers,
-Matt

[Mnemoria]

You may find this
http://www.crystalradio.net/tubeplans/index.shtml
of interest as a starting point - the three jpgs linked under the heading "Miniature-Tube Set Works On Flashlight Cells" in particular

[Otto Von Pifka]

truthfully, I would just use a modern radio board under the baseplate and bullshit in a tube radio on top.

look at the insides of real radioes for the basic shapes and features you need to cobble together.

the valves can be mimicked and backlit with LEDs and really be safer and simpler.

perhaps you could get one of those crank up emergency radioes they seem to be selling everywhere? incorporate the crank on the side of the base box and the radio section under the fake crystal/tube set.

I know they make some bigger, more expensive ones that do 8 or 9 different radio bands.
a bit overkill but it would be fun to tune some shortwave noise for effect.

[Horse Brass]

If you really want working valves in your circuit, I'd reverse your idea, and use battery powered valves for the tuning, and a hidden transistor amp to drive a speaker. Valves use higher voltages to get a reasonable amount of power out of them, like you need to drive a speaker. The tuning stages are working with a small signal anyway, and can get away with lower voltages. Or you could use headphones.

For an idea of what a home made portable radio would have looked like in the 30's and 40's, have a look at these Hikers radio plans from old magazines. Mnemoria has already given you the other site I'd have linked.   Or just google for 'one tube radio' or 'one tube regen' and you'll find dozens of other sites.

Now if you want some inspiration on how a steampunk radio should look, Tom Kipgen's site has things that make me wish I could build radios that look half as good!

[elShoggotho]

Does it even need to be powered? You can catch broadcasts with a crystal radio, if need be.

[Matthias Gladstone]

It did; in the end, I found a 1960's transistor radio set that fit the bill; i'm currently modifying that instead. The problem I had was finding the right valves - plenty about, but either too expensive or not the right type.
-Matt

[chainmailleman]

You will need upwards of 150 volts DC to get the valves to work properly. You could build a small vibrator circuit with a step-up transformer to overcome this issue using a small 12-24 volt battery. Other than that there are many schematics for valve radios, even here on brassgoggles. (some by me)