Tony,

Thank you! I'll try your suggestion of placing additional caps in
parallel with the existing bypass caps.

Incidentally, I found a spare set of 6146 tubs, installed them in the
SB-401 and tuned-up on 80 meters. Even though I didn't neutralize the
tubes, the '401 exhibited the same behavior I described above. This
suggests the problem is not with the tubes, but with some other
component.

Yeah, come to think of it, little or no grid current isn't anything
much to worry about. The 6146s are pentodes. Their grids shouldn't
draw much power, in any. I think the narrative in the manual is
misleading.

-Dave, K3WQ

Hi Dave

when you'll have done the test, please let me now as I am curious to know
whether the extra capacitor helps.

The screen capacitor is the most critical one because, if the screen does well
shield the plate from the grid, the neutralization bridge gets obviously
altered.

Yes, there should not be much grid current. Anyway, if you get the RF output
power you are supposed to get, you may forget that grid current issue and you
would be all set.

73

Tony, I0JX
Rome Italy