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Old 28th October 2013, 06:46 PM   #2531
6L6 is offline 6L6  United States
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You will probably run out of heatsink before you run out of transformer. You may need a fan.
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Old 28th October 2013, 07:02 PM   #2532
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2A bias and +/-32V rails = 128W dissipation pr ch. the 5U chassis should handle that.
transformerwise. 300VA pr ch will be minimum. so 800VA will for sure do the job
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Old 28th October 2013, 07:05 PM   #2533
Mallard is offline Mallard  Germany
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Ok, thanks 6L6.
What are the typical bias values other F5T builders?

Most likely I will use the 1Ohm source resistors and try to bias as high as possible by beeing able to touch the heastsink for more than 10 sec.

And will see what the result is.
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Old 28th October 2013, 07:34 PM   #2534
6L6 is offline 6L6  United States
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Quote:
Originally Posted by AudioSan View Post
2A bias and +/-32V rails = 128W dissipation pr ch. the 5U chassis should handle that.
I thought we were talking about 2A/device (2A*32=64W, *4 =256W/channel)

Sorry.
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Old 28th October 2013, 07:40 PM   #2535
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that would have been hot as a dual mono amp 500+W.
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Old 28th October 2013, 07:41 PM   #2536
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Quote:
Originally Posted by Mallard View Post
Ok, thanks 6L6.
What are the typical bias values other F5T builders?

Most likely I will use the 1Ohm source resistors and try to bias as high as possible by beeing able to touch the heastsink for more than 10 sec.

And will see what the result is.
that WILL result in a burned up amp. it is NOT the heatsinks that limits your bias. it the point where the diodes starts cunducting.
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Old 28th October 2013, 11:55 PM   #2537
Mallard is offline Mallard  Germany
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Sorry AudioSan, I just need to collect what I've learned from you

When I use two 0.68Ohm resistors in parallel and adjust a 340mV bias then I will end up at roughly 2Amps per channel? And in your point of view the 5U chassis can handle that?

Quote:
Originally Posted by AudioSan View Post
it's 2A pr ch. 1A pr device.
dual 0.68ohm resistors is just about right. then he will have 340mV at 2A pr ch.
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Old 29th October 2013, 12:16 AM   #2538
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correct.
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Old 10th November 2013, 04:04 PM   #2539
aft is offline aft  France
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Hello,

I'm planning to go for that f5T journey (V2, no cascode, stereo based on last board from diyaudio).
I'm already preparing and have collected usefull informations but still have doubt about matched components.
Can somebody explain :
- What active components need matching whithin a channel ?
- I can remember that the Aleph-x was requiring matched resistors, is that the same here ?
- Is there a need for matching between channels ?

Thanks. Raoul
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Old 10th November 2013, 04:13 PM   #2540
Zen Mod is offline Zen Mod  Serbia
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-if possible , input Jfets need to be of same Idss ; if going to multi output pairs route , all N need to be matched , and all P need to be matched
-if you buy Metal Oxide ones , they're already in enough low tolerance ; if using white ceramic ones (wirewounds) , buy more and measure them (with ccs , measure voltage drop)
-preferably , but not so important

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