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boxdoctor · 12th Feb 2018, 10:56 am

Mention of sound distortion reminds me about one of these sets I had on the bench in about 1975, with sound distortion when the battery voltage fell below about 12 volts.
The problem turned out to be self-oscillation of the power regulator transistor which was of the later silicon type. It only oscillated (at H.F.) in a narrow band of supply voltages around 12 volts. A ferrite bead fitted directly onto the emitter pin of the reg. completely cured the fault. Tony.

12th Feb 2018, 10:56 am	#9
boxdoctor Rest in Peace Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 785	Re: Marconi 4816 1590 survivor! Mention of sound distortion reminds me about one of these sets I had on the bench in about 1975, with sound distortion when the battery voltage fell below about 12 volts. The problem turned out to be self-oscillation of the power regulator transistor which was of the later silicon type. It only oscillated (at H.F.) in a narrow band of supply voltages around 12 volts. A ferrite bead fitted directly onto the emitter pin of the reg. completely cured the fault. Tony.