[Heathkit] Heathkit Digest, Vol 109, Issue 17 SB Series Filters

[G3OOU at aol.com]

Hi All
 
The SB series CW and AM filters only have four crystals (whereas the SSB  
filters have six) so the adjacent channel and stop band rejection will not be 
as  good. I have opened up some SB series filters to repair them and 
discovered dry  joints, fractured tracks and some of the toroids had loose turns 
due to no  retaining varnish. Most of the internal PCBs had not had the 
solder flux cleaned  off although this appears to be less of a problem due to 
good sealing.
 
If your filter(s) show significant ripple, possibly due to ageing, try  
putting a temporary 3.395MHz tuned circuit across the input and then the output 
 connections and see if the ripple can be reduced by adjusting the tuned 
circuit.  Crystal filters generally tend to be more sensitive to variations in 
their load  impedance rather than their source impedance.
 
73

Bob

Bob F Burns
C Eng,  FIET, MSE
Amateur Radio Callsign: G3OOU
Registered RSGB  Instructor
G-QRP Member No: 6907; Zone: 14, QRA: IO91WH; WAB:  TQ25
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