K790

"Matthew"

It's a power MOSFET.

............ Phil

Thanks Phil. It looks like that's it.

Btw, it says: N-FET / 500V / 15A / 150W

My mixer amplifier claims to be 150W per channel. There is 4 of those transistors in my amp. Would it really be 150W a channel?

Thanks.

"Matthew" "Phil Allison"

The dissipation figure of the output devices is related the possible power output from an amplifier using them in a fairly complicated manner:

Most audio power output stages operate in "class B " - which means the efficiency can be as high as 75 % at full power. Efficiency is simply the percentage of DC input power that winds up as output for the loudspeaker - the rest is just waste heat in the output devices.

With a "class B" amp the maximum device heat dissipation happens at about

So - for your 150 watt amp, that maximum will be at around 67 watts output with about 60 watts of heat lost in the two MOSFETS or a mere 30 watts each !!

They will still get pretty hot at that power level but are not at risk of failure.

To obtain the rated 150 watts dissipation a device MUST be mounted on an INFINITE sized heatsink or be fluid cooled like a car engine !!!

For a practical sized heatsink ( even with the help of fan cooling ) about

It helps if is no mica insulation used - ie the heatsink is left electrically connected to the device and must therefore be insulated from ground and finger contact.

............ Phil

Thanks for that Phil. Very helpful.

I am just wondering if my transistors are counterfeit. All they have on them are K790 and a small L4 or L5 writing below it. This amp was made by a very unknown Chinese place and I got it imported from China over ebay.

"Matthew"

The vast majority of equipment manufacturers are *far too wary* to have any dealings with non authorised suppliers - plus expect to buy on

So the short answer is - it is very unlikely.

.......... Phil