[Hammarlund] Phasing control null on crystal filter for SP-600

[Bob Young]

I put a new faceplate on my SP-600 which has been recently aligned. I have 
noticed that the nulls are not 180 degrees apart and are very broad on the 
phasing control and I can't even align the knob with the arrow correctly the 
nulls are so broad although I think I matched the marks on the shaft pretty 
well. Is this something I could have perhaps done when I took it apart or 
could it have drifted since it was aligned , it has had a lot of use since 
it was aligned about 6 months ago (it was all gone over and performs well). 
The null was nothing like on my HRO-60 however which is razor sharp and 
exactly 180 degrees apart but it did get rid of the hets pretty well. Does 
this indicate maybe I should realign it, perhaps it drifted off the resonant 
frequency of the 455 crystal? The Hammarlund manual unlike the National 
manual is not very clear on why you are doing things, is L-37 perhaps a null 
adjustment? Thanks,

Bob young
Millbury, Ma