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 Post subject: Adjusting DC Bias issue
PostPosted: Sat Mar 12, 2016 11:04 am 
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Joined: Tue Feb 02, 2016 12:32 pm
Posts: 7
In the process of adjusting dc bias. Got to step 9. In adjusting VR1, after much CW turning I got to 15mA, but it wouldn't go any higher even after I continued to turn CW. I didn't proceed to step 10 and VR2 adjustment. What now??

Not sure if germane, but at step 4 when I first turned on power supply, the DMM read .09mA, but after a few minutes it dropped to 0.00mA.

73 Paul KC2NYU


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PostPosted: Wed Mar 16, 2016 10:09 am 
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Joined: Tue Feb 02, 2016 12:32 pm
Posts: 7
Jim - sent below email on Sunday afternoon, haven't heard anything back so not sure it got thru to you. I am kind of stymied for the moment on proceeding with DC bias phase setup.

73 Paul
------------------------------------------------------------------------------------

Jim-
- with amp on gave it a good shake- it did not key.
- Turned VR 1-4 all the way CCW ( so "all the way" is about 20-25 full turns? Can you go to far?)
- Keyed the Amp and got 4.97V at the DRV pin closest to DRV
- Turned up VR1 10-15 turns, with amp keyed, measured voltage at Q1 gate. Got 3.57V


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PostPosted: Fri May 06, 2016 8:02 pm 
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Joined: Sun Mar 20, 2016 4:50 pm
Posts: 6
You might have a bad pot (as I did). On mine, VR4 would not adjust at all. Found pot wiper not adjusting resistance at all despite turning the adjustment screw many turns.


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