[Collins] 75A-4 BFO

[Glen Zook]

Try adjusting the "dial drag" on the front panel.  If this is too loose the frequency will shift when turning the passband control.  If it is too tight then it will take a lot of effort when tuning the PTO.  At least that is how my 75A-4 works.

When properly adjusted my 75A-4 is so close that I cannot tell any frequency shift.

Glen, K9STH

Website:  http://k9sth.com


--- On Sat, 7/5/08, wabate <wabate at verizon.net> wrote:

The next order of business is the passband tuning.  It does not track the main tuning well.  The spec I read says that the frequency should not change more than 50 HZ when tuned throughout the range.  Is that realistic?  Mine is much worse than that.  Probably a few hundred HZ. I've read the alignment a half dozen times.  I think I follow it OK.  I tried recentering the knob but that did not help.  I tried adjusting L-31 as the simple approach and that did not help so it looks like I'm in for the "difficult" approach.  I don't have the 6 KC filter so I will use the 3.1 and limit the tuning range to 1.5 instead of 2.5.  I will hook of a frequency counter to the phones terminal and start tweaking.
 
Anyone done this before?  Tips?  I have not seen any write ups on this.