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Vintage threads from the first ten years
| previous: Ken Gilbert Andrew, is the secondary a center t... -- 11/20/1999 5:49 PM |  |
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Re: Bias circuit design?
 11/21/1999 8:43 AM |
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Andrew | Re: Bias circuit design? Hi Ken, Thanks for the reply. The amp is a rebuild of a Deluxe Reverb. I ordered the trannie custom wound locally, speccing 650V/ct and showing a bias tap @ 50V. Unfortunately they interpretted that as 50V measured from one end of the secondary (i.e. 275V from the CT) Argh... Ok, so I started looking at an older Marshall that derives the bias from the main secondary winding, and pretty much copied what they had in there, and connecting to the 275V (since there's a wire there, I figured I might as well use it!) Problem is I only get about -10V max available to the actual bias point (junction of the 2x220k's to the grids of the 6V6GT's) The AB763 schematic calls for ~-35V I think (though dunno if that's at mid point of adjustment or what?) I'm assuming it *is* mid point, which means I should see ~-50V available at max. One other thing that has me worried: what voltage are the caps in the Marshall bias circuit rated for? What do you reckon? I'm thinking of ringing the trannie winders back to see how much they'd charge me to rewind it the way I really wanted, as I'd much prefer to stick with the original circuit. Cheers Andrew |
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