A linear amplifier I purchased secondhand worked but there had been some work done on it which was quite poor. The Plate RF choke has been damaged at some time in the past, and was repaired by using a soldering iron on the winding in 2 places. The anode suppressors consisted of a number of different types of resistors, and some were actually missing the connection wire and badly charred. The same amplifier had a softstart circuit added using thin telephone or Bell wire for the 240V AC connected to the time delay relay. They were removed and re wired with proper 240V rated, and correct colour cables. The RF plate choke was removed and replaced with a homemade one, using a text book design, and the suppressors rebuilt with better components. Some overheated and badly corroded RF cables were also replaced. This video shows the testing of the new Plate RF choke for self resonance. A choke with a self resonant frequency in any of the amateur bands could become damaged due to the high voltages and currents that occur in the choke.

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