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Old 21st December 2019, 05:36 PM
Richard Richard is offline
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Join Date: Dec 2005
Location: Notts
Posts: 5,114
Default Re: PSU III transformer information.

Hi Philip, yes reading some more, the LM317 divider will also be part of the load. Using 240R at R1 results in 5mA or using 120R at R1 results in 10mA. Phono 3 uses 4.2mA.

LM317 TI data sheet here,

A good calculator for this regulator here;

Morgan Jones also covers a floating HT supply using the LM317. To lower the current/heat in the divider he uses R1 at 1K and acknowledges that without load the output voltage will rise (as the divider alone will not be loading sufficiently). With many amplifiers this would be ok when connected but with the tiny load of Phono 3 it would be worth Bob checking the total load.
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