[AMRadio] KW restoration and need a bit of help on this one

[Donald Chester]

I put my plate current meter from filament transformer midtap to ground.  I 
return the grid bias supply/grid leak to the filament transformer.  That 
way, the plate current meter reads plate current only and the grid current 
meter reads only grid current.  I use a pushpull final with separate grid 
and plate current meters, so this requires two separate grid leaks, one for 
each tube, a separate protective bias supply for each tube, and of course, a 
separate filament transformer for each tube.

For the class-B modulator I put the meter from filament xfmr to ground, so 
it reads total cathode current, but that reading is less critical than the 
plate/grid current of a  class-C final, and under normal operation the grid 
current to a class-B modulator is only a tiny fraction of the plate current, 
so it makes little difference.

I never liked putting the plate current meter between the hv transformer 
midtap and ground, unless the filter caps are returned directly to the 
transformer.  Otherwise, the charging current of the filter caps shows up on 
the meter, and with large enough caps, could actually damage the meters on 
startup.  The bleeder needs to go to the fil xfmr as well, or else the meter 
will read plate current plus bleeder current.

Don k4kyv

_________________________________________________________________
Check out MSN PC Safety & Security to help ensure your PC is protected and 
safe. http://specials.msn.com/msn/security.asp