new ampli with IRF240

[slideman82]

I find I can do it roughly by starting off with bias as low as possible and playing music.
To start with the music is distorted until you tweak the bias to the correct point slowly.

That's the best way to do it... and you'll keep the lower QC... mine don't runaway thermally at quiescent, but starts to warm up pretty fast... and I also tried 4 ohm version, with to-220's, and I didn't fail!

Do the drivers need to be connected to the heatsink?

 

[nigelwright7557]

Do the drivers need to be connected to the heatsink?

I do it without the heatsink connected but watch out for it warming up.

The transistors can warm up very quickly if the DC offset is high or the bias is set too high.

 

[cbdb]

The ccts not wrong there using the R as a decimal point (like the K in 4k7 ) So R14, 15 are .33 ohms and R17 is .22 ohms.

 

[quasi]

I have run IRFP amps with no heatsinks and had no problems at small audio levels.

However if the DC offset is high or the bias is set too high they will quickly destroy themselves.

I dont set the bias to a set current I just set it just high enough to get rid of crossover distortion and have no problems.

With or without a Vbe. With high enough source / drain resistors thermal runaway can be controlled.

I do it without the heatsink connected but watch out for it warming up.

The transistors can warm up very quickly if the DC offset is high or the bias is set too high.

We are talking power amps here yes? Testing without a heatsink using IRFP240's or similar is risky indeed.

Cheers
Q