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 →

Used Equipment Sale

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It was a successful well attended evening at the Village Hall in Aisthorpe for the Lincoln Short Wave Club Used/Surplus equipment sale (some junk), with our resident auctioneer Bob G7AVU trying to extract the last penny from the bidders. As usual there was a lot of humor with the usual suspects trying to wind Bob up, and people frightened to scratch their head as Bob would take this as a bid. Steve M5ZZZ was running round the table trying to find the items for Bob to sell and at times struggled to find the items (if only they had been … 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 →

Regional RSGB Club of the Year Presentation

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Steve Boden G4XCK Regional Manager for Region 13 Presenting Lincoln Short Wave Club Chairman Mark M0ZLE with the RSGB Regional Club of the Year Shield, watched on by Ian G4XFC who designed the layout for the LSWC entry and local Deputy Regional Manager Steve Burke M5ZZZ The presentation was well attended by club members and everyone enjoyed the buffet meal provided by our club secretary Pam G4STO and Steve M5ZZZ. A toast was given for our late Chairman Chris Jones G0PIO who suddenly passed away at the end of November last year. It was noted that is was the hard … 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 →

INTERMEDIATE COURSE & EXAMINATION JUNE 2013

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The Lincoln Short Wave Club will be holding an Intermediate License course starting Saturday 1st June 2013. The course will be held every Saturday and Sunday throughout the month of June 2013 the examination being held on Sunday 30th June 2013. Candidates for the course should in the first instance complete the contact form on this website or visit the Lincoln Short Wave Club at The Shack, Village Hall Lane, Aisthorpe, Lincoln. on either Wednesday Evening from 19.30 or Saturday mornings from 09.30. The club Training Officer is Les Clarke  G1LQB he will be happy to take your details and register you for … 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 →