[Hallicrafters] Troubleshooting an SX-71

[Rodney Bunt]

This behavior is indicative of a poorly tracking tuning capacitor.
 
I have seen this on a Hammarlund SP-200. Where there was a miss alignment between the mixer and RF

stages, it would align only at one place on the band top or bottom or middle but never over all of

the band. Use the "blades" on the tuning CAP to trim this.
 
Because there are three tuning caps....
 
1. adjust the Oscillator segment to track the dial scale for frequency. Set top, set bottom, and 
adjust blades (bend in or out) to adjust linearity against the dial scale.
 
2. inject RF signal generator at grid of mixer, adjust "MIXER" cap segment to obtain good output 
across the bands
 
3. Inject RF at grid of RF tube and ajust RF cap for same...( good output across band.
 
4. Adjust antenna matching for good broad response for each band segment....
 
Rodney
VK2KTZ


--- ARDUJENSKI at aol.com wrote:

> (SX-71) It is apparent that on every band, however, that there is more  
> sensitivity at the upper end of the band than at the lower end.  This  
> might be poor alignment, but because it is the same for all bands,  I 
> was wondering if it may be part the receiver's design? Any good  references 
> raddressing peculiarities with the SX-71? I did GOOGLE search and  checked the 
> archives
>  
> Alan  KB7MBI
> Woodinville, WA
> Member ARRL / ARCI / ARS / FISTS /  NAQCC
> 
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