[Collins] 75A-4 Low sensitivity on 11 - 10 - 10 Meters

[Jim Walker]

Hello:

 

I am in need of some trouble shooting advice. My 75A-4's sensitivity
while in
The 11/10/10 meter positions are very poor. Other
band positions produce excellent signals in all modes along with strong
calibrator marker signals. The calibrator on the three high bands is
barely discernable.
The 11/10/10 T-7 coil and C-16 variable capacitor are functional. I have
gone through the manual's RF alignment
procedure several times and have also changed out V2 to no avail. I put
in the best 12AT7 into V4 that I have.  The antenna Peak trimmer
produces ambient noise increase on each band but the signal are way low
compared with the SP-600, R-390, 75A-2 and the ICOM 746.  Should I be
suspicious of C-22, the 24 mmf (pf) padding capacitor?  I do have low
plate (175 v 190)  and screen voltage (140 v 175) on the 6DC6 (which I
also checked and substituted) but R11 reads 33.6K and R6 is 4.7k.  The
grid resistor R11 measures 1.15 meg in circuit. Any other suggestions?

 

 

Jim 

KZ5AW