Building a 1920s crystal wireless set

It's great fun building you own electronics and making them with ancient components is a little more changeling, but still fun.
the build
First off you'll need a chassis or box to build it in , in this example I've used a 1923 'Mo..phone' box, (can't read writing on front, lol) that was about £15 on line including postage, some damage will bring the price down, but it's fun repairing the box too.

Fixing a support after partition made.

This one came with silver plated hinges and a lock and key, normally they will be brass or anodised steel. Originally the black baseboard would have been Ebonite, an early form of rubber moulded sheet, used later to toughen tires edges for cars, but not available anymore, but PVC sheets in black can be found on line and they are much easier to cut. This box had slots inside for a partition wall for the headphone/coils box on the right side. I cut a piece of hardboard to fit in those slots.

 Next you'll need a circuit diagram. This is one of the most simple and commonly used in early wireless receivers, 1920-24.  From left to right a receiving or aerial coil, bridged with a variable tuning capacitor (if a fixed one is used only one frequency would be picked up, similarly with varying lengths of wire for a coil with a fixed capacitor will give you different frequencies too!. Next is the crystal or diode, followed by a capacitor that removes the broadcast frequency, this is not needed if long headphone cables are used as they have the same capacitance (around 200pf) and finally the headphones, about 2 thousand ohms in resistance, modem types are not suitable as they are around 8 ohms.
How it works

Fig A - A transmition signal at a given frequency is generated at the transmitter as a sinusoidal waveform.

Fig C. The strength (or amplitude) of this signal is varied by an audio waveform (Speech of music) this makes the transmition signal now look like this.

Fig D. When the signal if fed through the crystal diode it can only travel in one direction, so the negative part of the waveform is removed. The human ear can detect positive or negative signals (b/w 50 hertz -15 thousand hertz) but not when going at full waveform (the top part is a mirror image of the bottom part) so they both cancel each other out to the ear.

Fig B. show that the waveform when defused by the capacitor across the headphones (200pf)

This diagram show the circuit drawn a pictures of real components rather than circuit symbols. So as you can see you'll need 5 components and need to wire them like here. Next you'll need to lay out the components on the ebony base with a balanced layout, this is jut to make it easier on the eye, looks more professional. Capacitors in the early days were referred to as 'condensers' and the fixed one shown here is 100pf or 0.001uF. Two ways of displaying the values.

When buying old components on line the most expensive part is the crystal diode sometimes called the detector. But a reasonable price is about £20, a guy in Italy makes new ones for around £35 with postage. A used 1920s tuning capacitor is around £10, similar price for headphones and aerial coil. The coil needs to be around 100 ohms resistance or about 1.5 micro henry for medium wave with 300 pf tuning capacitor. I buy box loads of old parts, that brings the cost down. The fixing bolts are no longer made, so shop around for them too.  The wiring, to keep original looking is 18 gauge SWG tinned copper wire, and where wire cross I use fibre coated sleeving.

The big brass tuning capacitor I used had a slow motion gear, so on the coarse spindle I wrapped some 18 SWG wire to use as a pointer and later painted it red. The numbered dial came form an old chassis I found once, you can make one on you PC. The coil socket cost me £5, but you can also use speaker sockets instead. I've made around 5 of these types of radios so far, some with valves and others without, but the most collectable types are the crysal sets as you need little knowledge to to them going, just a length of wire for an =aerial and a good earth (radiator or gas pipe, etc)