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Old 22nd January 2011, 07:41 AM   #1
Green77 is offline Green77  Sweden
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Default TubelabSE R31 and R32?

Hello.
Been looking at the schematic for 5 min now and i can't find R31 and R32 (4,7K 1/4W). It's in the partlist. Wrong in the schematic or the partlist?

Thanks/ Daniel
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Old 22nd January 2011, 02:59 PM   #2
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Parts list is correct. Scroll down 2/3 way here till you see "Tubelab SE update".
"Increase the grid stopper resistors on the 5842 (R31 and R32) from 1K to 4.7K ohm. These resistors should be carbon composition if at all possible. The 5842 will oscillate if ..."
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Old 22nd January 2011, 03:02 PM   #3
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They are grid stoppers for the 5842 driver tubes, and, now that you mention it, are not shown on the schematic......

IIRC, the 5842's are prone to oscillation and George probably added these after the schema was posted during subsequent tweaking and testing of the design.

They are located between R8 and the grid of the driver tubes.
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Old 22nd January 2011, 04:35 PM   #4
Green77 is offline Green77  Sweden
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ok, so they will be in serie with rca input and pin 4 on 5842. right?
and r8 goes to ground before R31..
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Old 22nd January 2011, 09:27 PM   #5
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Quote:
Originally Posted by Green77 View Post
ok, so they will be in serie with rca input and pin 4 on 5842. right?
and r8 goes to ground before R31..

Yes, between the top of R8 and pin 4. If you were doing a point-to-point build, you'd want the grid stopper right on pin 4 with as short a lead as you can solder. In this case, it goes on the PCB like any other component.

As mentioned, carbon comp can work better than metal film in this application since they have less inductance. I have MF in my amp presently, but I'll probably try CC very soon.
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