Tag Archives: high voltage

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)

Lincoln Shortwave Club Posted on by

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 →

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 →

Valve Linear Amp Safety

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Valve Linear Amplifiers WILL  KILL!!!  If you make a mistake there is no SECOND CHANCE, so you have to be VERY VERY careful before you start working inside them. I am writing this because of some stories I have heard that frighten me, as we are talking about HIGH VOLTAGE in excess of 2.5 THOUSAND VOLTS with high current which is a lethal combination. and I hope that I have managed to scare you into taking notice of the safety measures which should be adhered to. I have worked with mains voltages and above since the age of 16 and … Continue reading →