[Collins] 75A4 sensitivity

[Bill Russell]

This might be a long question.....
I have a 75A4 that exhibits a lot of background noise. I will try and explain.
The 7 deadly caps have been replaced by the previous owner although the 
value is larger than the originals. When I got the radio, it would overload 
very easily. I found that the IF transformer for the AGC amplifier was way 
out of adjustment and I had very little AGC voltage. After alignment of 
this IF can, I now have plenty of AGC voltage and no more overload but the 
gain of the radio seems very high. With the IF gain control set at minimum 
and the s meter sensitivity also set at minimum, I always have a noise 
level of at least S9. When I remove the antenna, the S meter will fall to 0 
but as soon as I connect the antenna its back up S9 or more. When I set the 
AF level for a comfortable listening level on a fairly strong station, the 
background hiss is very annoying. Its not noisy band conditions because 
when I switch to my SP600 or NC303, the band is quiet. As a matter of fact, 
my SP600 S meter will read about S1 but the A4 will read S9 to 10 over!!! 
Remove the antenna and back to 0 on the S meter and the background hiss 
will drop but I think its still noisy.
Any ideas will be greatly appreciated.
Thanks much,

Bill Russell
KC2IFR