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Old 2nd February 2010, 04:23 PM   #6901
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Quote:
Originally Posted by cviller View Post
I ordered some 2SJ618/2SK3497 from digikey, but I'll have to wait a while before I get them. I'm looking forward to play around with them - they are relatively new, so there is not much info on them on the forum.
Looks interesting -- forward conductance is nearly twice the IRF parts -- but input cap is a lot higher as well.
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Old 2nd February 2010, 04:25 PM   #6902
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Post 6883 A Wayne... he shows heatsinks intended for LED lighting products... I'd not run fans myself, since they add noise to the room. One might get away with a squirrel cage blower running off a much much much slower (&quieter) motor, and ducted to run air up and along the fins. It doesn't take that much air to greatly improve the effective heat transfer... one could turn the thing on with a thermal switch too...

One could approximate their size by "unwrapping them" and figuring the thermals for a 3" high and X" wide heatsink of similar fin construction... probably still not enough heatsink.

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http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
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Old 2nd February 2010, 04:25 PM   #6903
cviller is offline cviller  Denmark
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Yeah, so I might not use two pairs for the F5s.
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Old 3rd February 2010, 04:45 AM   #6904
erpiii is offline erpiii  United States
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One could approximate their size by "unwrapping them" and figuring the thermals for a 3" high and X" wide heatsink of similar fin construction... probably still not enough heatsink.

_-_-bear[/QUOTE]

I'm trying to find out what the power dissipation is on those heat sinks... I know the highest output for one of the arrays that can go on that heat sink is 56 watts. So, if I can get some dissipation numbers on those arrays, then maybe some assumptions can be formulated. Does anyone have any figures on what the max dissipation is on the output devices in the F5 at around 25C?
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Old 3rd February 2010, 11:20 AM   #6905
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by erpiii View Post
Does anyone have any figures on what the max dissipation is on the output devices in the F5 at around 25C?
it's all in the pdf.
dissipated power = bias current times voltage across the FET.
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Old 3rd February 2010, 02:49 PM   #6906
erpiii is offline erpiii  United States
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HI Andrew!

Okay... I'll bite.

"the F5 is a push-pull ClassA amplifier that when biased to 1.3A can deliver ~2,6Apk of ClassA current to the load.

If the load is 8r0 then the maximum ClassA power is 27W ([2 * 1.3]^2 * 8 / 2)"

Andrew T.

"BTW,
27W is equivalent to 54Wpk. i.e. both are 20.8Vpk and 2.6Apk into 8r0."

Andrew T.

Does this mean both devices +/- are at 54Wpk? For a total of 108W per channel? Does that mean both channels would dissipate 108Wpk?

Mr Pass says that the F5 power consumption is 180W 8ohm @ 25W

How do these numbers relate?
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Old 3rd February 2010, 03:52 PM   #6907
AndrewT is offline AndrewT  Scotland
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do you want output power to the load?
or
do you want dissipated power to the heatsink?
Don't confuse the two.
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Old 3rd February 2010, 04:15 PM   #6908
erpiii is offline erpiii  United States
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Quote:
Originally Posted by AndrewT View Post
do you want output power to the load?
or
do you want dissipated power to the heatsink?
Don't confuse the two.
It would be the dissipated power to the heat sink... I'm trying to relate it to other heat sinks... If I can find out their dissipation as well.
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Old 3rd February 2010, 04:18 PM   #6909
AndrewT is offline AndrewT  Scotland
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post6905 reminds one of the way to arrive at dissipation power.
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Old 4th February 2010, 06:21 AM   #6910
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Default Choke Loading an F5

What happens when the output of an F5 is choke loaded (with a big @ss choke)?

I know the output impedance changes to whatever the parallel inductor is...but is a coupling cap (always) required as well?

Thanks in advance,

Chris

p.s. threads of interest that deal with similar questions:

Choke Loads for Zen/Aleph Amps
Choke Loaded Zen

Last edited by chrismercurio; 4th February 2010 at 06:30 AM.
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