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Re: Fender Blues Deville electrical problem

Posted by unclejed613 (A) on December 24, 2006 at 15:10:54

In Reply to: Fender Blues Deville electrical problem posted by moshik on December 16, 2006 at 02:17:16:

check the bias voltages on v3(12ax7). your cathodes should read +34vdc, and even though the dc voltage for the grids aren't shown on the schematic, i'm guessing they should be somewhere around 33vdc (class a operation grid bias is between 0 and -1v according to the data sheet), or maybe a bit lower (since this IS a class ab output stage), since cutoff is -6v. plate voltage should be between 200 (class a operation) and 350 or 400 (class ab operation, where the tube is closer to cutoff).
that's the driver stage. on the output tubes, uou should have 0 on the cathodes, -18-20v on the grids, about 450v on the screens and about
470v on the plates.

pinouts of the tubes:
6L6:
P 3
S 4
G 5
K 8
F 2,7

12ax7:
Ka 3
Ga 2
Pa 1
Kb 8
Gb 7
Pb 6
F 5,9,4

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