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Old 12th January 2018, 01:43 PM   #15791
wdecho is offline wdecho  United States
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F5 power amplifier
Mighty Zen, where, how did you find the Iq of 1A6. Like to learn something.
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Old 12th January 2018, 03:37 PM   #15792
Zen Mod is offline Zen Mod  Serbia
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F5 power amplifier
took it arbitrary

set what you like .... say to 55C at heatsinks , measure just to be sure that both channels are in same bracket and that dissipation is still sane ( which will be , except in case that you are using Gargantuan size heatsinks)
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Old 12th January 2018, 04:17 PM   #15793
wdecho is offline wdecho  United States
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Originally Posted by Zen Mod View Post
took it arbitrary

set what you like .... say to 55C at heatsinks , measure just to be sure that both channels are in same bracket and that dissipation is still sane ( which will be , except in case that you are using Gargantuan size heatsinks)
Gotcha
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Old 20th January 2018, 12:30 PM   #15794
wdecho is offline wdecho  United States
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Fired up the F5 but did install .47 resistors but not the current limiting circuit. It is installed on big heatsinks and with .59V bias is running 25C. How high have others biased this amplifier? This is just a project so I am going to turn it up but am just curious how high the other FAB have biased their build. I will turn up till it reaches 55C on the heatsinks close to the mosfets.
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Old 20th January 2018, 12:44 PM   #15795
indra1 is offline indra1  Indonesia
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Originally Posted by wdecho View Post
... just curious how high the other FAB have biased their build. ...
Find a cozy place of your own somewhere between
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Originally Posted by chede View Post
... As a first step I switched the power transformer to 20V secondaries and had rails with 24V-ish voltage, still with the Aleph J. Set bias to 2.0 amps, so roughly 48W per MOSFET, which still worked with my heatsinks....
and here.
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Originally Posted by Zen Mod View Post
I'm not Fearless Amplifier Builder , as Papa certainly is ..... and I'm anyway used to make unnecessary changes to his circuits , so some trace cuttin' and one additional resistor , change of trimpot value , multiturn just because I'm Chicken
And never forget the master FAB principle by Papa here.

Last edited by indra1; 20th January 2018 at 12:49 PM.
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Old 20th January 2018, 01:40 PM   #15796
wdecho is offline wdecho  United States
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How do you adjust a bandsaw blade. You tighten it till it breaks and then back up some.

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Old 20th January 2018, 01:53 PM   #15797
indra1 is offline indra1  Indonesia
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As Papa sez, X*?@! is reserved for the more mature constructor. You absolutely qualify beyond reasonable doubt.
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Old 20th January 2018, 02:16 PM   #15798
AndrewT is offline AndrewT  Scotland
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How do you adjust a bandsaw blade. You tighten it till it breaks and then back up some.

I just love this method.
Precisely clear when too much.
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Old 20th January 2018, 02:30 PM   #15799
wdecho is offline wdecho  United States
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F5 power amplifier
Right now I have the bias up to .9V and it appears to be running cool directly on the mosfets and around the mosfet at the heatsinks. My heatsinks are so big that the are still around 25C. I am yet to see how it sounds but last night I was surprised on how good it sound. I say this because this is one build I have sighed away from because others have said it would be too bright on horns. It was not the case with my horns.

I have plenty of mosfets indra1 so it is not a big deal if I burn up some. Just playing. Whether they last is another matter. I will keep members informed especially on the difference in sound. Supposedly they sound better the more you run them up.

Last edited by wdecho; 20th January 2018 at 02:32 PM.
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Old 20th January 2018, 02:34 PM   #15800
AndrewT is offline AndrewT  Scotland
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Originally Posted by wdecho View Post
Right now I have the bias up to .9V and it appears to be running cool directly on the mosfets and around the mosfet at the heatsinks. My heatsinks are so big that the are still around 25C. I am yet to see how it sounds but last night I was surprised on how good it sound...........
Yet we have a body of opinion insisting that semiconductors must run HOT to perform well.
Run them as cool as you can manage and stay within the electrical parameters required for good audio performance.
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