Radionic Regen
 

Just for fun I put together a valve regen receiver using (mostly) components from Radionic construction sets. It runs off 12 volts for both filaments and HT. The output stage is in the style of a late 50s / early 60s hybrid valve/transistor car radio. Medium wave is fine but because of the lack of screening and fine tuning it's no fun to use at higher frequencies. I think I might add a metal front panel, fine tuning, some screening and maybe a ground plane and see how it goes. You can see it in more detail here:
https://www.youtube.com/watch?v=dwLHzm9sfcc

Re: Radionic Regen
 

That's superb Tim, well done!

If you could fold it into a box shape and add some LEDs l bet some steampunker would pay hundreds of pounds for it!

Congratulations.:thumbsup:

Re: Radionic Regen
 

Visually, adding metal plates to it would lose a lot. It's stunning as it is.
Maybe a glass display case to keep the dust off it?

David

Re: Radionic Regen
 

Thanks for all the kind words.
I tend to agree that metal plates would spoil the look.
Perhaps someone on here could quickly invent a transparent screening material? :)

Re: Radionic Regen
 

How about Star Trek's 'Transparent Aluminium'!;D

Re: Radionic Regen
 

Can those 807s withstand such a high HT?Their lives might be shortened by a hundred years with this sort of abuse.:)
Great project though. Anything to be gained by using e.g. metal 6L6s?( won't look as good though)

Re: Radionic Regen
 

Yes I'm sure metal valves would help, but amazingly it seems that 'transparent aluminium' has already been invented!
"ALON® or Aluminum Oxynitride is an amazing and unique transparent advanced ceramic that is polycrystalline (made from powder) with a cubic spinel crystal structure. In the popular media and in the Star Trek community, it is commonly referred to as Transparent Aluminum. Surmet is the only company globally, that manufactures ALON®."
I can't find any mention of it's screening properties though. My gut feeling is that compounds of aluminium don't behave like the metal when it comes to RF. Does anyone know? (Bound to be too expensive anyway!).

Re: Radionic Regen
 

Wow, that is a really creative and interesting looking radio with lots of attention to detail. I have never seen a radio built like that, it is very impressive.

I have always been totally enamored with the hybrid car radio style audio design. Part of this is that the input impedance to the grid of the driver valve (typically an EF98) can be 10 meg ohms, and the class A output stage can drive a 4 ohm speaker, that is a huge impedance transformation, from just the two devices aided by the transformers despite the base current hungry output transistor.

I liked the hybrid and 12V HT valve idea so much I once built one, using an OC16 as the output stage. The only snag I found was that the ECH83's triode wasn't too good over 12MHz, so I had to abandon it for the L/O and use an MPF102 for the 5.7 to 18.2 MHz short wave band. The coils were hand wound, except the Miller IF cans.

Its also fun to work on "12V valve gear" where you don't get zapped! There is a photo of the superhet radio I made here:

http://worldphaco.com/uploads/THE_EF98-OC16_RADIO.pdf

Re: Radionic Regen
 

That's a beautiful looking radio! An absolute cracker.
I stumbled across the hybrid car radio audio approach recently and it appealed to me straight away. I tried to use negative feedback over both stages as in the Philips N3G82VT but it it seemed to increase distortion! I settled on a design based on the circuit in the Mullard 'Reference Manual of Transistor Circuits' (1961). Mine uses an EF98 driving a 2N3055. I thought I might change to something more authentic like an OC16 or OC26 later on but I didn't want to lose a vintage transistor while experimenting. I've tried the radio using Denco range 4 coils (5MHz-15MHz) and it's certainly lively but frankly a nightmare to operate because of the lack of screening.

Re: Radionic Regen
 

Screening happens through conductivity. Conductivity simply shorts electric field components. Conductivity allows alternating magnetic field components to create circulating eddy currents and the mag field from these currents cancels the arriving mag field on one side, and creates a reflection on the other.

No conductivity, no screening.

Metals have freely available electrons to do easy conductivity. In metal oxides, the electrons are a bit tied up and not available for conduction.

Of course, in Startrek, they only have to re-tune their transporter to emit a beam of Nurgulon particles (or some such) and they can convert any material into an electric conductor.

By the way, Faraday screens have slots to disrupt eddy currents, so they only stop electric fields, and let magnetic fields straight through, making them useless for radio screening. Doesn't stop lots of peple sticking the name Faraday in front when they really mean an ordinary screen. It's a bit like saying 'colander' when they mean 'saucepan'.

David

Re: Radionic Regen
 

That's a fabulous looking piece, from the age of 14 I've always wanted to build a regen set but have never got around to it - maybe one day and I hope it turns out half as good looking as yours

Re: Radionic Regen
 

There are also magnetic shields made of magnetic material with a high initial permeability. They act as a low reluctance medium for the path of the magnetic flux, diverting it away from the space to be shielded. Often these are used to minimize mag fields getting into audio transformers or unwanted deflection of CRT beams, which is why many scope CRT's have Mu metal shields. If amazingly good shielding is required, two or three concentric shields will do it. This type of shield also makes for a good electrostatic shield too.

Pretty well any conductor makes a good electrostatic shield though, and you can have a good electrostatic shield, without a magnetic shield, if the shield is not a closed loop, like those used between a primary and secondary of a power transformer where the ends of the foil are insulated (or they would make a shorted turn).

Re: Radionic Regen
 

A fine mesh, brass would be in keeping.

Re: Radionic Regen
 

Any metal will transmit some light, if you can get it into an even layer just a few atoms thick. For instance, the front of an EL panel is metallised on the inside, a few atoms thick, and it conducts well enough to maintain the same voltage over the surface while still transmitting nearly all the light from the electroluminescent material. (The current drawn is tiny.)

How about using half-silvered glass? :idea: With no illumination from within, and therefore nothing to transmit (any light coming in through one of the half-silvered panels and out of one of the others will be doubly attenuated, once on the way in and once on the way out), it would just look like a plain mirrored box. Switch on some bright lights inside the box, though, and you would be able to see the insides clearly, the transmitted light swamping out the reflection.

Re: Radionic Regen
 

Then you will end up with a David Copperfield style magic show.

Re: Radionic Regen
 

I had a Pye TRC 1000 using only an OC16 output transistor in my Vauxhall Cresta - it worked a treat.

Peter

Re: Radionic Regen
 

Tim
Would you elaborate on the transformers used in the hybrid EF98 / OC16 output stage in your build? I recall that Argus25 used a genuine purpose designed transformer in his stunning creation,did you maybe repurpose yours from another application?
I have had a long term interest in this tech but leaning toward S'het designs and have two PYE TRC1000 car radios but would not wreck either for its transformer.
Your build certainly looks very appealing and is wonderful visually-well done there.

Mike

Re: Radionic Regen
 

Hello Mike
For the driver transformer I used an original Repanco TT20 (measured turns ratio 22:1) which was intended for this role. For the output transformer I used the low impedance secondary of the well known RS Universal Output transformer (still available) as an autotransformer with tappings A and D used for the load and tappings D and C connected to the 8 ohm speaker. I left the primary (high impedance) side disconnected. This gave me an impedance ratio of about 4:1 which worked nicely, but left the speaker with a constant 9ma of DC current. I felt I could live with that.

Re: Radionic Regen
 

Great stuff Tim

I have been thinking of a hybrid build as I have several of both pre TO3 types of OC16 stud mount Transistors of the type used by Argus25 and even predating the type he used.
Had thought of having the transformers specially wound but your iteration sounds very good.

Mike

Re: Radionic Regen
 

Silvered glass will stop electric fields, but it's useless at magnetic fields in the RF range.
To screen mag fields you either need conductive metal thicker than the skin-depth at that frequency or else you need a ferromagnetic material. Normal aluminium boxes are thick enough to screen RF, but at the lower frequencies of mains fields, the thickness needed (skin depth is frequency dependent and conductivity dependent) would be impractical, so CRT screens are usually made out of good magnetic 'conductors' like mumetal.

THere is a snag to mumetal on CRTs... it can get permanently magnetised, just from getting a knock and being in the Earth's magnetic field, od from being worked. So you need to thermally anneal them after manufacture before they can be used.

David