[Hallicrafters] Using to wider filter from the SR-150 (2.7kc) in the SR-2000 (2.1kc)

[James Liles]

Hi Mike:
I have swept a number of SR-150 filters and they indeed average 2.7kc.  Can find no reason for Hallicrafters to have printed misleading data in the operations manual.  A good reference is page 11 of the SR-150 Performance specifications document i.3.    (-3 db limit at 400 cps to 600 cps) and (-3 db limit at 2700 cps to 3200 cps).  There were no filter variations from the "A" to "C" level which is the most current.   

The following information will clarify the installation of the SR-150 "2.7 kc filter into SR-2000 which uses a "2.1 kc" filter.   First, if you are a contester, don't do it.  It sounds great but 2.7 kc is a bit wide.  

The difference between the filter circuits is as follows.  L14 and L15 in the SR-150 are adjustable from 40uh to 240uh.  L15, the filter source in the SR-2000 is the same inductor as used by the SR-150 but L16, the terminating inductor is 17uh to 39uh and the capacitor that parallels it is 300pf --- much higher Q and different impedance than the terminating circuit in the SR-150. 

You can go two ways here.  Simply drop the SR-150 filter into the SR-2000 and accept approximately 3db to 6db of filter ripple or replace the terminating inductor with the one removed from the SR-150, copying the capacitor and resistor.  Leave the input termination alone, it does not appear to affect the filters performance.  The termination is the cause of the filter ripple. 

I believe my post a few years back did not reference the termination or filter ripple.  The filter ripple was measurable but quite undetectable to the ear. 

Kindest regards Jim K9AXN