The Redruth Radio Receiver KIT AM and HF AM bands One Transistor Easy Build


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This is a kit you need to solder the components. Build instructions can be downloaded from but hard copy included.

One Transistor design not an Integrated Circuit – be amazed at the quality from just a single transistor.An easy well laid out board makes this an idea biginners project. Quality board with solder mask- quality teflon variable tuning capacitors.
This is for the board and all components -you will need to provide  a pair of standard earphones with 3.5mm jack  and a short aerial for AM band and longer for the HF band. 
This is a one transistor micro power design you can use the on board CR2525 battery button cell,
power is switched off when earphones are disconnected. The earphones are not supplied, but any  standard type not crystal earphones will work.  
Brass stand offs included but not the plinth. 
Kit contains silk screened board with solder mask, two crocodile clips for ease of connecting earth and aerial to the pads on the board. External tuning pins should you wish to further extend the frequency range with a vane type variable capacitor.
Frequency Range 800k –  3.6MHZ and 6MHZ –  27MHZ. Fitting an external vane type capacitor can increase the Frequency range – just connect across the pins provided.
This radio gives crystal clear reception good separation with the correct aerial.
Tuning is by two on board variable  capacitors. 
Button cell holder provided for 3 volt cell.  ( batteries not included) Pads are also mounted on the board for external  power supply. 
Full assembly instructions provided. 
Other ranges could be provided by changing the two onboard inductors.
This receiver can also be powered by a 3 volt 100mA solar cell  ( not Provided in this listing). You would need to remove the on board cell when using a solar cell. 
During the day the radio will work on AM with usually just a short indoor aerial or earth connection. For HF  reception of long range signals an  earth connection may also be  required. 
There are no coils to wind. 
This is a very simple one transistor ( Darlington)  receiver using the minimum of components. The sound quality is excellent but reception will very much depend on atmospheric conditions. For worldwide reception an external aerial will greatly enhance the performance of this radio. This works on standard modern headphones.Headphones not included. 
Please email should you require further information. 
Overseas buyers you only pay one postage charge regardless of the amount of kits. Free UK postage.

Redruth radio instructions

Redruth Radio Receiver Assembly Instructions

Fit D1 and D2 these are the same, observe the line on the diode with the line on the board.
Fit R1 100K resistor ( Brown Black Black Orange )
Fit L2 the 270uH inductor for the AM band. (Red Violet Brown ) AM band
Fit L1 4.7 uH inductor for the HF band. (yellow Violet) HF band
Fit C2 The disc ceramic capacitor marked 104
Fit the Transistor, the flat on the transistor is marked on the board and faces outwards.
Fit C1 the 10uF electrolytic capacitor, observe the polarity.
Fit the tuning capacitors.C4 this is the Brown one it rotates continuously and is used for coarse tuning control. These can be fitted either way and are not polarity sensitive.
Fit the tuning capacitor C3 brass one this is for fine tuning control.
Fit the battery holder for CR2025 /2032 – 3-volt cell. The clip is at the top of the board. There is an alternative pad for external 3-volt battery supply. Remove cell when using an external supply.
Fit the 3.5mm stereo jack socket. Ensure this is parallel before soldering and pushed in so the strain relief plastic lugs are secured in the holes on the board.
Fit the 2-way switch for band selection.
Fit the two pin header on the earth and aerial tabs for fitting an external variable capacitor this will lower the bottom frequency of each band.
When the board is complete, connect a short aerial and switch to band 2.Band 2 will be the strongest band during the day and is best for testing the receiver. HF reception is best in the evening or with a longer aerial and earth during the day. You will have to experiment with the aerial and earth connections when signals are stronger, particularly in the evening. Removing the earth can stop stronger signals breaking through.

Two crocodile clips are provided for connecting an aerial and earth to the board.
The Circuit Explained.
This is what is called an Audion circuit. The transistor is doing both the detecting and the amplification. This has the advantage of minimum components and the output can use lower impedance headphones. The radio will work with any standard 32 Ohm stereo headphones. The socket is not designed for a mono earpiece. An indoor wire aerial will work well , but for more sensitive HF reception you may require a longer outdoor aerial. The transistor used is a Darlington driver transistor which gives the maximum output of a single transistor package. The radio will work with other NPN type transistors. A pin header socket could be soldered and different types of transistors fitted if you wanted to experiment.
The aerial input is marked A and the Earth is marked E on the circuit board. The two diodes are used to drop the voltage down to 2 volts and to protect the circuit if the battery is accidentally connected the wrong way. The power consumption of the radio is microamps so a cell will last a long time even if left switched on.
Use stereo phones only. Mono phones will short out the output.
Removing the headphones removes the power from the circuit- remove headphones to preserve on-board battery life. Remove external power supply if using to preserve battery life when radio not in use.
These instructions can be emailed to you in color for reproduction. If you require further information please email.
Expanding the frequency range of the receiver. It is possible to connect an extra external variable capacitor across the E and A terminals to expand the range of the receiver or use the two pin header If the onboard capacitors are left in the circuit they can be used for fine tuning with an external variable capacitor.
Frequency Range Band 1 HF 6 Mhz to 27.5MHZ These are approximations, tolerance of components may vary the frequency range.
Band 2 AM 800 kHz to 3.6 MHZ


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