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Old 28th August 2011, 12:27 AM   #1
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Default Sizing output stage

How much power could one reasonably expect to get with 2 pairs of TO-3 250W 16A Lateral FETs. Like the Exicon ECF20N20/ECF20P20. http://www.profusionplc.com/images/d...s/ecf20n20.pdf

My guess is about 200-225 Watts with good cooling.

So it would be resonable to make a 65-75 Watt 8 Ohm amplifier, with enough power to drive 4 Ohm loads without trouble.

Am I totally off the mark?

Last edited by Neutrality; 28th August 2011 at 12:31 AM.
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Old 28th August 2011, 02:09 AM   #2
jcx is offline jcx  United States
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Default Officailly Class (A)B can be 70% efficient into resistive load

Class A?

for Class AB you can get 2-3x the (real) power dissipation of the Q/heatsink combination - which as a rule of thumb is about 1/2 the manufacturer's power rating with big but practical heatsinks
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Old 28th August 2011, 02:14 AM   #3
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Quote:
Originally Posted by jcx View Post
Class A?

for Class AB you can get 2-3x the (real) power dissipation of the Q/heatsink combination - which as a rule of thumb is about 1/2 the manufacturer's power rating with big but practical heatsinks
Class AB.

Hmm, that was my thought as well, My first guess was around 250 Watts maximum but reduced it to 200-225 Watts because I thought it might be expecting too much of just 2 pairs.

Well, then 90 Watt 8 Ohm, 180 Watt 4 Ohm should be feasible. Or 75 Watt 8 Ohm,150 Watt 4 Ohm, with capability to somewhat drive a 2 Ohm load without the amp blowing up.

Also arent Lateral FETs a little more rugged due to their negative tempco?

Last edited by Neutrality; 28th August 2011 at 02:19 AM.
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Old 30th August 2011, 01:45 AM   #4
djk is offline djk
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A Hafler DH500 will do 600W/3Ω with three pair of the 8A/125W outputs, with two pair of the 16A/250W devices and a good heatsink you should be able to do that too.
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Old 30th August 2011, 09:10 AM   #5
AndrewT is online now AndrewT  Scotland
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for FET output stage, add up the total 25degC power ratings of all the devices in the channel.
Divide by 4.
That is the maximum ClassAB output power into a severe reactance speaker load used for domestic listening.

When using BJTs in the output stage divide by 5 or 6 to get an estimate for the domestic listening maximum output power into severe reactance speakers.

2pr 250W (Tc=25degC) FETs will allow ~250W of maximum power.

2pr 250W (Tc=25degC) BJTs will allow ~160W to ~200W of maximum output power.
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Old 30th August 2011, 09:12 PM   #6
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The lateral FETs have a high self-limiting Rds and can be run harder than a BJT without a fancy limiter.

The DH500 has a total of 750W of outputs and can reliably deliver 600W into a load (when cooled properly). I used them for PA for more than 25 years, they work well for mids and highs, sound a bit muddy for bass.
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