[Drake] TR-4 S-Meter sensitivity help

[Bill Abate]

Hi all, After months of the rig sitting idle, I decided to 
tackle the S-meter circuit again.  The rig is a TR-4CW, SN 
44XXX.  When I first got the rig a few years back, I aligned 
it and fixed a few minor problems.  The rig was working 
fine.  Sensitivity was about .5 uv for 10 db on 40M.  S-9 
was about 140 uv.  Cal produced about 20/9.

About a year ago the s-meter suddenly went stingy.  Cal only 
produced about S-8 on 40M.  A check with the sig gen showed 
the sensitivity was OK.  Went into the circuitry and checked 
V11, V12, V15, V4 and V17.  I could not find any components 
out of spec and tube substitution did not help.

The sensitivity pot is at max sensitivity and it takes 1000 
uv to get S-9.  RF sensitivity is slightly lower at 1 uv for 
10 db.  Anybody been down this road before?  Any suggestions?

Thanks,

Bill, K3PGB