A couple of week's ago I found an amplifier using the 2SK1530/2SJ201. But later in the text I found out you can use the IRFP240/9240. But then even later in the text they even said you could use IRF540/9540.

Could anybody please tell me why you can use these transistors with no modifications, and what could possible be the difference.

It is posible in some schematics. I replaced few years ago some FET ( lateral Hitachi MOS-FET ) from an pro amplifier ( Carvin - FET450) with IRFP240/9240 and it work very well.

But I don't think is OK for every schematics. Anyway you can try to replace and work with a single pair. If it will don't blow in the first 10 second you have a chance.

Regards !
The 2SK1530/2SJ201 are Tosiba Lateral MOSFETS. These are designed specifically for Audio. They have a negative temperature coefficient and do not suffer from secondary breakdown/thermal runnaway, thus not needing temperature compensation via mounting the Vbe multiplier transistor on the heatsink. If this IS done it might cause crossover distortion before or after the amp has warmed up depending on where the bias is set.

The IRF device are HEXFETs (D-MOS) and do suffer from secondary breakdown and it is adviseable to use temperature compensation with these. Not only is the capacitance different, but so is the Vgs ON, thus they need a higher voltage bias than the Toshiba/Hitachi devices.

I've seen an amplifier (Hybrid) that the designer gives referances to using both lateral or IRF devices and this design includes a Vbe mupltiplier but no mention of transistor mounting is included. However there is a suggestion for changing bias set ups (I.E. different R values) to account for the differing bias needs and to make ajustment easier. The OPS is a Source Follower.

These are the main differences I see between these two types of transistors aside for the price. The Lateral types are much more expensive, but more rugged and OPS designs for these can be more simple.

I would be wary of dropping IRF devices in place of lateral in any amplifier that doesn't have Temp. compensation. This could be disasterous (particularly with Source Follower configurations), with the simpler Japanese designs such as the MJ amp or similar. However if the OPS is a Complimentary Feedback type with driver transistors using a Vbe multiplier it is conceavable that you could swap the two and only have to tweak the bias.



the toshiba 2SK1530 only have negative temperature coefficient above a bias current of 8 Amps has you can see in his data sheet.

As 8 amps is not pratical in a power amplifier theiy need temperature compensation via mounting the Vbe on the heatsink.
as the bias currents usualy used are much smaller.

The Hitachi family of mosfets (2sk133,2ski34,2sk135 and his equivalents 2sk1056,2sk1057,2sk1058 and the respectives complementarys) are the only ones that i knew that have a negative temperature coeficiente above 100mA.


Jorge Santos