K790

Anyone have information about transistor K790? I'd like some info about it. There is 4 of them in my mixer amplifier.

Thanks.

Reply to
Matthew
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"Matthew"

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

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It's a power MOSFET.

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

Reply to
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.

Reply to
Matthew

"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

Reply to
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.

Reply to
Matthew

"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

Reply to
Phil Allison

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