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Old 19th October 2006, 10:07 PM   #1
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Default 12AT7 Linestage design

I was fooling around in TubeCAD and was wondering about the following linestage. It has nice bandwidth and a comfortable gain of just under 3. What do you think?

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Old 19th October 2006, 10:15 PM   #2
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Quote:
It has nice bandwidth and a comfortable gain of just under 3.
And that nice vertical load line should manage to get the distortion below 15%.
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Old 19th October 2006, 10:27 PM   #3
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>curseword<load of feedback

that reminds me on AR line of preamps........ tons of feedback without actual need ;hehe-they sound exactly the same- sound without actual cause

12AT7 have mi in range of 70 ,academically speaking.....and wasting that to 10 db is blasphemy; at least for me.

Ra for first stage is too small
same for second stage
(this is explanation of Sy's post)
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Old 19th October 2006, 10:36 PM   #4
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ouch. ok then, back to the drawing board
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Old 19th October 2006, 10:40 PM   #5
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Rule of thumb: when you decide what gain you want from the line stage, look for a tube with a mu 1.5-2 times higher.
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Old 19th October 2006, 10:46 PM   #6
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Default Re: 12AT7 Linestage design

Quote:
Originally posted by sorenj07
I was fooling around in TubeCAD and was wondering about the following linestage. It has nice bandwidth and a comfortable gain of just under 3. What do you think?

Click the image to open in full size.

Positive feedback to the cathode, it decreases stability.
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Old 20th October 2006, 02:00 AM   #7
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One of the primary reasons to use a cathode bypass cap
is to keep the gain high if you arn`t after a lot of gain leave
the cap out. Eleminating this cap gives you a little local feed
backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.
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Old 20th October 2006, 02:51 AM   #8
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Quote:
Originally posted by woody
One of the primary reasons to use a cathode bypass cap
is to keep the gain high if you arn`t after a lot of gain leave
the cap out. Eleminating this cap gives you a little local feed
backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.

Do you describe how to turn this multivibrator into the Shmitt's trigger?
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Old 20th October 2006, 02:59 AM   #9
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well, here's another crack at a linestage, using the lower-gain 12BH7 tube. I've heard it's more linear than the 12AU7, which was my natural next recourse. I had the plate curves in front of me when fiddling with bias and stuff so hopefully this one turned out better.

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Old 20th October 2006, 03:19 AM   #10
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The grid of the second stage appears to be floating. DC to the plate of the first stage?
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