Projects
Two Valve Short Wave Superhet
Written by Bryce Ringwood   

This is a project for a short-wave radio covering 3.0 to 6.5 MHz (approximately), it therefore covers the 90, 75, 60 and 49 metre broadcast bands, as well as the amateur 80metre band. It is only a two-valve radio, so please don't expect it to be a communications receiver. On the other hand with a decent aerial, it will receive many broadcast stations and the occasional AM amateur transmission that can be heard on 80m. In theory, it should be able to resolve SSB transmissions, but so far, I have had little success. On 90m, you will hear the BBC, Transworld Radio and  RSG. You will also be able to receive VOA, channel Africa and others on the other broadcast frequencies. (Oh dear - so many stations have gone missing since I built this set.)

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Simple Crystal Set Radio Receiver
Written by Bryce Ringwood   

 

Introduction

Crystal set (xtal set) radios were developed at the turn of last century and were used to receive early broadcast transmissions until valve (or vacuum tube) radios ousted them from about 1920 onwards. Nevertheless, crystal set radios have always remained popular with home constructors, who have tried to achieve more and more performance with many fantastic designs.

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1 Valve Regenerative Receiver
Written by Bryce Ringwood   

Introduction

This is a simple one-valve radio for AM reception from approximately 500kHz to 1.8MHz. It should be possible to build it over a weekend and it doesn't require any special tools other than a soldering iron, multimeter and electric drill. Layout of parts is not critical and although I have not tried it with other valves, I suspect that any triode-pentode or double triode may be used. I built it to fill the gap between crystal sets and superhet radios in my collection. I made two of these radios and they both worked really well.

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1 Valve Fremodyne VHF Receiver
Written by Bryce Ringwood   


Introduction
 

During the 1950's, FM broadcasting was introduced in many countries as a means of producing high-quality radio transmission, and also to prevent further congestion of the AM medium wave band. “FM” stands for “Frequency Modulation”. In this mode of transmission, the frequency of transmission varies in sympathy with the sound waves being broadcast. (In an AM transmission, the strength of the signal varies.) Because an FM transmission requires a wider bandwidth than AM, FM broadcasting is done on VHF (Very High Frequency) in the 88 to 108 MHz waveband. (AM  is broadcast on low frequencies between 480 kHz and 1.6MHz). There are other benefits to FM broadcasting, such as the huge reduction in noise and atmospherics, also FM radios work inside steel and concrete buildings, whereas AM does not.

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A Battery Eliminator for Battery Portables
Written by Bryce Ringwood   
 
Note this project is intended to assist with your own design - rather than being a "recipe"to be blindly followed. There are a few simple formulae so that you can adapt the design to your own requirements. Don't get too carried away with the numbers - the supply voltage at my house can be anything between 170 and 320 volts. Capacitors can have a 50% tolerance.  
 
Battery portable radios and table radios using vacuum tubes have  been around since the beginning of the valve era. Prior to World War 2, Accumulators (Lead-Acid batteries) were used for the filament supply, and the high-tension supply might have been provided by either dry-cells or small accumulators in series. This explains why valve filament voltages are often multiples of 2 volts - approximately.  Note that with battery valves, we talk about the ...
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