. 
Hi Nelson, no I didn't! The weather was too nice here on the east coast to sit inside and play with potentiometers. Definitely will do it though.
correct bias
Hi! i am confused. hope someone can help.
i can´t bias my F5 to 0.6 v (R11/R12). when i have .36 v the voltage at R3/R4 is 4.6 v. what is wrong?
the temperature of the heatsink (which is 300 x 150 mm per channel) is after (2 hours) 46 celsius, the transistors about 72 celsius.
thanks, mario
Hi! i am confused. hope someone can help.
i can´t bias my F5 to 0.6 v (R11/R12). when i have .36 v the voltage at R3/R4 is 4.6 v. what is wrong?
the temperature of the heatsink (which is 300 x 150 mm per channel) is after (2 hours) 46 celsius, the transistors about 72 celsius.
thanks, mario
hallo andrew,
thanks for your answer. but i don´t understand "Rth c-s". please, can you explain?
thanks, mario
thanks for your answer. but i don´t understand "Rth c-s". please, can you explain?
thanks, mario
Thermal resistance between mosfet and heatsink. What can mean no or wrong paste,wrong type of insulator, loose screws, convex or concave surface of heatsink near mounting point or broken thermometer ;-D
yes, R11/12 are 0.47 ohm (= R47 ohm, right?). other idea?
i think, the insulator between transistor and heatsink is a (pink) silicon-pad, no paste. if the surface is ok, i have to check in the next days.
thanks, mario
i think, the insulator between transistor and heatsink is a (pink) silicon-pad, no paste. if the surface is ok, i have to check in the next days.
thanks, mario
Hi!
meanwhile, i tried some things:
a) decrease/increase R3/4 from 1.1 k to 9k: 1.1k was worst (bias: 0.07v), 9k also bad (bias: 0.12v); best 2.2k with bias o.24v and 4.3v over R3/4
b) decrease/increase R19/20: nothing happened
c) decrease/increase R13/14: nothing happened
d) power supply is +/- 25.7 v
maybe the jfets (sj74/sk170) or transistors (IRFP240/IRFP9240) are the problem?
any ideas are welcome 😕
thanks mario
meanwhile, i tried some things:
a) decrease/increase R3/4 from 1.1 k to 9k: 1.1k was worst (bias: 0.07v), 9k also bad (bias: 0.12v); best 2.2k with bias o.24v and 4.3v over R3/4
b) decrease/increase R19/20: nothing happened
c) decrease/increase R13/14: nothing happened
d) power supply is +/- 25.7 v
maybe the jfets (sj74/sk170) or transistors (IRFP240/IRFP9240) are the problem?
any ideas are welcome 😕
thanks mario
just measured some temps on my F5. sinks baseplates run at 45c right at the middle outputs (2pair version) transformers run at 34c.
ambient is 25c and bias is 1.7A (0.85A pr Device)
looks like i need to pull up the bias some more😀
ambient is 25c and bias is 1.7A (0.85A pr Device)
looks like i need to pull up the bias some more😀