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- Posted on
March 24, 2005, 6:23 am
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** 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
They will still get pretty hot at that power level but are not at risk of
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.
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
** Semiconductor counterfeiters mainly go after the service, spares and
hobby electronics markets - where the buyers are all utterly clueless
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.
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