PSU III transformer information.

[Richard]

Hi Bob, I know little about these but a look at the data sheet suggests a minimum 10mA load. The web design may be good but I wonder if the tiny 4 or 5mA load of Phono is enough? I may be reading the data incorrectly but if it does need a bigger load you could fit a resistor across, 25K would give 10mA loading for example. Perhaps someone more familiar can help

[pre65]

Originally Posted by Richard

I may be reading the data incorrectly but if it does need a bigger load you could fit a resistor across, 25K would give 10mA loading for example. Perhaps someone more familiar can help

Excellent idea Richard. I've did that myself on my single ended Mosfet amp bias supply when low current draw was evident.

25K @ 10ma = 2.5W, so 5W (or more) to be safe.

I'd use a 25W Arcol (only 12.5W unless on a heat sink)

https://www.ebay.co.uk/itm/Arcol-HS2...wAAOSwcmZa51jV

[Richard]

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,
http://www.ti.com/lit/ds/slvs044x/slvs044x.pdf

A good calculator for this regulator here;
http://www.learningaboutelectronics....calculator.php

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.