Category Archives: Home Brew

The LSWC 2018 Construction Contest

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Wednesday 21st saw the LSWC hold their annual Construction Contest for the Joe Rose Memorial Trophy. Last year saw us two different versions of ATV transmitter. One being for home use including a partly assembled water cooled power amplifier (For an update see below) built by Adrian M0NWK. The second, and also the winner for last year, being a fully portable transceiver in a case built by Jason G7KWP. Adrian M0NWK This year Started off with a similar theme. Adrian M0NWK, started off by showing us his Arduino powered controller for a comtech 23cm ATV transmitter.             … Continue reading →

Arduino Satellite Controller Motor Control

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This part of the project is to help you understand how we are going to control the motors of the rotator and we are deviating from the 2rpm motor to a higher rpm to be able to quickly move from one location to another at a higher speed then slow down to be able to follow the path of the satellite. In the previous post I gave links to the parts needed and for this part of the project, we will be using the H Bridge, 2 motors, and the Arduino Nano. I have found a good video which explains … Continue reading →

Refurbishing a Linear Amp (Part Four)

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After serious thought on the layout of the components on this Linear Amp especially the placement of the filament transformer and the position of the RCA 813 valves for cooling, I decided that the best thing to do was to remove everything and reposition it better within the chassis. Initially my thoughts were to sort the amp out and get it working keeping the same layout, but as I progressed I was not happy with the layout, so this has now actually turned into building a 1kw Linear Amp from some recycled parts as I am now modifying a lot … Continue reading →

Refurbishing a Linear Amp (Part Three)

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Because of finding dangerous faults during this project, this Linear Amp was not a refurbishment but a complete rebuild. I would advise others not to do this work unless they are experienced in what they are doing, as inexperience could result in DEATH as LETHAL VOLTAGES are involved. For reference, this linear is not pretty and is being brought back to life as a working project and will only be used safely in my shack, it will not be entered into any beauty contest. I changed the way the valve bases had been fitted to provided better ventilation by removing … Continue reading →

Refurbishing a Linear Amp (Part Two)

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Refurbishing the Linear Amp was still in progress, and because I was changing the old filament transformer for a proper center tapped transformer suitable for the amplifier, I had to change the circuit to take this into account. Another modification to the amplifier was the cathode bias circuit as the old circuit did not have one. R5 is a 50K 10 Watt resistor that biases the valve at cut of when not transmitting keeping the valves cooler and D5 is a 5 volt 10 Watt Zener Diode which biases the valve for transmission. For those not familiar with the grounded … Continue reading →

Refurbishing a Linear Amp (Part One)

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This is a series of articles doing a step by step refurbishment on an old homebrew HF linear amplifier. It has to be taken into consideration that when the Linear Amp was built everything at that time would be valves which were more forgiving unlike the transistors of today. The amp was 2 X RCA813 valves wired in grounded grid configuration and the input was fed directly to the cathodes of the valves with no matching network. (this was common in the old valve days) The first step was a visual examination of the linear and I was suspicious about … Continue reading →

Electrolytic’s! DON’T BLOW YOUR FUSE!!!

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Electrolytic’ Capacitors may smooth out our ripples but they do need some TLC or they will blow your equipments main fuse. They do benefit from a regular top up of electricity but some are neglected and need a little bit of extra TLC to bring them back to life. This short article is covering the poor neglected electrolytic capacitors that have not had an electron pass through them for a very long time and is to give you advice on giving them that extra TLC. More information on electrolytic capacitors can be found on the Wikipedia. While this topic is … Continue reading →

2.5 KV Voltmeter

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Having recently started being interested in HF Linear Amplifiers I needed a voltmeter to measure the High voltage on the anodes of the valves, I have a Bradley meter but it will only go up to 1.2 KV and I needed a 2.5 KV voltmeter to monitor the voltage on the Linear Amp that I was building. I had a 100uA meter in my junk box with a scale of 0 to 25 so I though that I would use that with a series resistor, (forget what it says on the scale as this can be easily changed) so the … Continue reading →