resistors for LT317 heater circuit

chokesrule

Member
2010-06-25 4:24 pm
Hi I am yet again tweaking my srpp lampizator...I have been reading Morgan Jones' Valve Amplifiers.....I changed the cheap rectifier diodes in my crc heater circuit to his suggested schottky diodes and heard a dramatic difference....so now I have decided to build Jones LT317 regulated heater supply (page 359)....it uses 150r and 600r to adjust the voltage to 6.3v.....Do these resistors need to be 5watt???The tubes are 6n6p and have a heater current of 750ma..sorry there are no pictures I have neither scanner or camera
 
Hi I am yet again tweaking my srpp lampizator...I have been reading Morgan Jones' Valve Amplifiers.....I changed the cheap rectifier diodes in my crc heater circuit to his suggested schottky diodes and heard a dramatic difference....so now I have decided to build Jones LT317 regulated heater supply (page 359)....it uses 150r and 600r to adjust the voltage to 6.3v.....Do these resistors need to be 5watt???The tubes are 6n6p and have a heater current of 750ma..sorry there are no pictures I have neither scanner or camera

Resistors can be 1 Watt... when you want to be really cautious make the 600R 2Watt. Voltage drop across these resistors is very small...
 

Arnulf

Member
2009-02-02 9:41 am
These resistors have rather negligible current running through them, voltage drop across the series is identical to output voltage. They can be as small as you want them to be (1/4 W is perfectly fine). Since regulator will try to maintain 1.25V between the output and adjustment pin, one can calculate presice value for current from the value of upper reference resistor and this voltage drop by using the well-known U = R * I formula.

If this was a CCS-type heater supply (there would only be a single resistor in that case) it would have to be pretty hefty. Not so in your case (CVS).