K790

"Matthew"



** If it is in a TO3P pack this a will be it:


http://www.donberg.ie/descript/2/2sk790.htm


It's a power  MOSFET.




............   Phil

On Thu, 24 Mar 2005 17:48:25 +1100, "Phil Allison"



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"



**  Quite easily.

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
45 % of maximum power output and is about 40 % of that maximum.

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
40 - 50  watts per TO3P device is the safe limit.

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

On Thu, 24 Mar 2005 19:01:43 +1100, "Phil Allison"



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"



**  Semiconductor counterfeiters mainly go after the service, spares and
hobby electronics markets  -  where the buyers are all utterly clueless
idiots.

 The vast majority of equipment manufacturers are *far too wary*  to have
any dealings with non authorised suppliers   -  plus expect to buy on
*credit*  and pay only if satisfied with the goods  AFTER  they have been
installed in manufactured products and proven to be OK.

So the short answer is  - it is very unlikely.




..........    Phil