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The BA-3 as preamp build guide
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Old 28th May 2019, 07:10 PM   #1441
nanchangbob is offline nanchangbob  United States
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I was just looking at 6L6's build and I noticed the MOSFETs are turned around, I know on some MOSFETS the drain and source can be reversed but I'm guessing it can not on these?

Does anyone have a part number for those heatsinks?
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Old 28th May 2019, 07:20 PM   #1442
nanchangbob is offline nanchangbob  United States
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I looked at the datasheet and I see the problem
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Old 28th May 2019, 08:50 PM   #1443
Zen Mod is offline Zen Mod  Serbia
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The BA-3 as preamp build guide
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just wanted to say that I'm better seeing details on your avatar than on pic you posted

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Old 11th June 2019, 04:31 AM   #1444
budwiser is offline budwiser  United States
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Uhg, do I have a problem. Hooked up across R11, R10 and R12 as instructed. After turning pots, only R11 is showing any activity. Got to .25 volts on R11 and still no activity across R10. R12 has stayed at zero. Am I doing something wrong.. afraid to go any higher. Should R10 increase proportionately to R11 as I turn P1.
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Old 11th June 2019, 05:49 AM   #1445
Hikari1 is offline Hikari1  United States
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R10 and R11 is your bias.

What you are referring to as R12 is your DC offset. But you do not measure ACROSS R12. You measure after R12 and ground. Plus probe of your meter on output leg of R12 or input leg of C3 and negative meter on ground...you can use the ground pad of the PCB.

I'd start with the pots back at zero and start the biasing procedure over again. Because you are not measuring the DC offset you don't know what's going on yet.

Don't be afraid to turn the pots until you get a reading across R10/11. But try to null the dc offset as you go...it's kind of a back and forth game with the pots. The mosfets won't turn on until they reach a specific voltage so sometimes you need to turn a pot a lot until a reading shows up on R10/11.
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Old 12th June 2019, 01:32 PM   #1446
budwiser is offline budwiser  United States
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Worked like a charm. Thanks



Quote:
Originally Posted by Hikari1 View Post
R10 and R11 is your bias.

What you are referring to as R12 is your DC offset. But you do not measure ACROSS R12. You measure after R12 and ground. Plus probe of your meter on output leg of R12 or input leg of C3 and negative meter on ground...you can use the ground pad of the PCB.

I'd start with the pots back at zero and start the biasing procedure over again. Because you are not measuring the DC offset you don't know what's going on yet.

Don't be afraid to turn the pots until you get a reading across R10/11. But try to null the dc offset as you go...it's kind of a back and forth game with the pots. The mosfets won't turn on until they reach a specific voltage so sometimes you need to turn a pot a lot until a reading shows up on R10/11.
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