[Hammarlund] HQ-170A S meter problems

[Joe W2KJ]

Have been chasing my tail trying to solve a problem with my
HQ-170A S meter.  Perhaps the great minds on this list can
help me out.

After warm-up the meter pointer is pinned to the left side of
the meter.  Only huge signals will move it upwards to the
right.  I cannot get the S meter to zero out at all nor can I
get it to "unpin" using the S meter ZERO ADJUST pot.

I have checked all the usual suspects, tube, resistors around
V13, etc.  Have replaced V13, the 12AU7A with several others
(checked OK on B&K 747B tester) and still have  the same
symptoms.

Interestingly, when I swap the 12AU7A for a 12AT7A, the meter
unpins and the pointer settles to about mid-range.  It will
swing upwards to the right on normal strength signals!!  The S
meter ADJUST pot will move the pointer left and right but
still will not zero the  meter pointer.

I have checked all the past digests with no luck as to what
might be causing the above problem(s).  Sure hope someone has
been able to solve this anomoly and can help me out.

                                vy 73, Joe W2KJ