Is the B+ tied to the grid of the 5687 in the cascode? Its not clear on the schematic.
Also thoughts about using center tapped filament transformer, AC heating on output tubes, in place of the balance pot. Should be easy to implement, but how does the sound compare?
The upper grid ( Ec2 as refered to in cascode plate curves ), is attached to an ohmic voltage reference. Fed a regulated current by the CCS 2, it is attached to the low-impedance output for maximum stability. See the CCS2 sub-assembly for the detail. B+ to the top of the CCS, grids to the lower source, and the other end of R-set to the R-bias( V_bias=i_regulated*R_bias ) and with a pair of 5687's V_bias ought to be ~60V. +5/-0 V. As drawn with LND150's i_regulated is ~0.2 mA so ~270k is a reasonable guess. regards, Douglas
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