[Hallicrafters] SR-2000 simplified adjustment for 6.5mc I.F.

[Jim Liles]

Good evening:

Since I keyed this up in a conversation on another site, I thought it prudent to share it here as well.  It describes a simplified procedure to align the 6.5Mc I.F. system in the SR-2000 and SR-400 transceivers; one of the most difficult adjustments to get right.  



The factory adjustment process used sweep analysis which I also used for years.  I’ll say it like it is @#$%^&.  Takes a lot of schmoozing.  Adjusting broadband amplifiers historically has been tricky when using sweep alignment.  Not going to explain the details here but will explain them fully on my web site when time is available.

I’ll probably get some flak for that statement but if you haven’t tried sweep analysis for broadband filters try it: even Collins uses swamping not sweep analysis for broadband filter alignment.

On my web site under service notes you will find the sweep analysis and swamping techniques.  I have not added the technique in this letter yet.



Since I wrote the sweep and swamping notes I have developed a super simple and field tested procedure.  It is easy and the results are as good as sweep analysis. 



1.    Remove V12 the Heterodyne oscillator tube.

2.    Band switch 14Mc.

3.    Frequency dial 14.050Mc.

4.    Scope probe 10X on V11AP2.  Will be looking for 6.5Mc at 3V PP.

5.    Tune mode.

6.    Go to transmit.  Don’t worry about Xmit RF settings. 

7.    Adjust T1 and T2 top and bottom slugs for peak.

8.    Set frequency dial to 14.450Mc

9.    Repeat step 7 noting which slugs need adjustment.

10. Set frequency dial back to 14.050.

11. Repeat step 7 at 14.450 and 14.050 until the adjustments do not need changing.

12. If you have been successful you will measure approximately 3 volts PP and when tuning the VFO from end to end the signal will not exceed 3db of ripple at the band edges.



You may wonder what we just did.  That broad band system is made to be 500Kc wide with a 3db skirt using tight coupling and adding a 2200 ohm resistor across each coil winding.  Tight coupling causes the output to look like a Bats wing and the resistor further flattens the shape.  The resultant wave shape rises at the beginning droops in the center and rises again at the end. 



What you just accomplished is peak the wave shape at the normal 14.050 and 14.450 locations which are the normal high points of the peak – droop - peak shape.  



There are photos of the waveform when properly adjusted in the service notes section of the K9AXN web site.



If this is unclear please send a comment so that I can restate it.



Hope you find it useful.



Kindest regards Jim K9AXN