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    Identifying the B+ and Bias tap in the MK IV, and other questions about VTA MK IV boards

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    Identifying the B+ and Bias tap in the MK IV, and other questions about VTA MK IV boards

    Post by Guest on Sat Sep 25, 2010 10:51 am

    I just bought a pair of VTA boards for my MK IV's. I am trying to determine which of the 2 wires that connected to the OEM bias circuit is the B+, and which is the bias tap. I was thinking the B+ is the red/black, and the green/yellow is the bias tap. Also the two green filament wires from the power transformer that were tied to the 2 & 7 pins of the octal; and then two twisted wires going from the 2 & 7 pins on that octal to the 4 & 5 points on the OEM board are now to be connected to the VTA board at points 4/5 & 9. Does it matter it matter which of the two green wires goes to 4/5, and which goes to 9. I can't detect a difference in color between the 2 wires, there may have been at one time but now I can't see any difference now. Thanks for your help! Roy is away until the 26th

    Bob Latino
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    Re: Identifying the B+ and Bias tap in the MK IV, and other questions about VTA MK IV boards

    Post by Bob Latino on Sat Sep 25, 2010 7:08 pm

    Hi Michael,

    The RED/BLACK wire is the power transformer's bias tap.

    The GREEN/YELLOW wire is the center tap for the 6.3 volt AC line and is grounded.

    The two GREEN wires carry 6.3 volt AC to the tube heaters. It doesn't matter which of the two GREEN's goes to pins 4/5 and which to pin 9.

    Bob

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