Working on a Power Supply (my first) for a headphone tube amp, And having a problem with the Heater supply. Thinking of doing something with a pair of 5842s. The Transformer was taken out of a SS amp and does not have a 6.3v winding. I have a 5 or 10. So I used some uf4007 and built a bridge rectifier on the 10v and comes out at 13v. then added a lm317 and getting 6.8v when I hook it up to my meter. But when I connect it to the heater pins on a tube, the voltage drops to about 0.4v. What am I missing?
LN317
the heater cold resistance is much lower than under working conditions. Therefore it can be, that this lower resistance is causing a current limit / short circuit protection of the LM317. Start up currents of tube heaters are much higher than the rated ( operation) currents.
the heater cold resistance is much lower than under working conditions. Therefore it can be, that this lower resistance is causing a current limit / short circuit protection of the LM317. Start up currents of tube heaters are much higher than the rated ( operation) currents.
As tubesteve mentioned - cold filament resistance is much lower than a hot one, and you may consider slow turn-on circuit for LM317. Another approach is to combine voltage regulator followed by current regulator based on two LM317s. It limits filament current to a defined value, ergo for lower resistance, voltage drop is also lower. Voltage regulator + lower resistance equals higher currrent.
I use the pre-regulator and current regulator to supply DHT filaments in a power amp.
http://www.diyaudio.com/forums/powe...tracking-pre-regulator-current-regulator.html
I use the pre-regulator and current regulator to supply DHT filaments in a power amp.
http://www.diyaudio.com/forums/powe...tracking-pre-regulator-current-regulator.html
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