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PJL · 17th Feb 2017, 11:41 am

You will also get hum if the output valves are not reasonably well matched. Push pull amplifiers rely on the cancellation of HT ripple in the output transformer. Measure the voltages across R45 and R46 to confirm the PX4's are passing roughly the same current.

17th Feb 2017, 11:41 am	#148
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Restore a Beau Decca You will also get hum if the output valves are not reasonably well matched. Push pull amplifiers rely on the cancellation of HT ripple in the output transformer. Measure the voltages across R45 and R46 to confirm the PX4's are passing roughly the same current.