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Old 29th December 2012, 11:45 PM   #81
buzzforb is offline buzzforb  United States
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Ikebana!
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Old 30th December 2012, 12:08 AM   #82
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Old 30th December 2012, 02:06 AM   #83
6L6 is offline 6L6  United States
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One output transistor?
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Old 30th December 2012, 02:30 AM   #84
buzzforb is offline buzzforb  United States
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Nope. There are two, just hard to see. 200 ohms will not do it, so i have to use bigger pot or put resistor in series. Didnt feel like messibg with it after i couldnt get bias up, so i will finish tomorrow. All else is good, functioning as expected. Tomorrow should go quickly.
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Old 30th December 2012, 04:37 AM   #85
Nelson Pass is offline Nelson Pass  United States
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Quote:
Originally Posted by buzzforb View Post
Ikebana!
Looks like my bench. But neater.

Don't be afraid to use clip leads....

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Old 30th December 2012, 01:13 PM   #86
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OK. Irritated now. Cant figure out what is wrong. Cannot bring bias up past about 1V. If I check the FE independent of the output transistors, all is fine. Attaching output transistors, I have 56V across Jfet until i bias it up and then everything levels up and I have 27V across both top and bottom fets. From there it goes nowhere. cat bring gate voltage pass about 1V. What is stealing my current? I have the negative input shorted to ground. Can get the offset close to zero, then it starts to wonder. Dont have the feedback point bypassed with cap, so ill try that to stop the wandering output.
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Old 30th December 2012, 01:30 PM   #87
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gimme exact schm which you're using , voltage across LTP drain resistor , voltages across Rs-es in output and output offset

it's wise to start troubleshooting with just one output pair , same as 9V1 zenners between G and S of outputs (you can pull it out later)
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Old 30th December 2012, 01:31 PM   #88
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buzz,
maybe R27 needs to be tweaked. That's what I did with the Mini-A with R100's.

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Old 30th December 2012, 01:48 PM   #89
buzzforb is offline buzzforb  United States
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Tea,
your schematic is too small to see.
ZM,
I am using the schematic from earlier in the thread given to 6L6. Fe is fine as far as I can tell. Found a little clue when testing bjt in ACS for Vdrop. When i connected one probe to the output and one to the gate of the bjt, all the sudden bias came up. I am assuming this points to bad bjt.
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Old 30th December 2012, 02:05 PM   #90
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