[HeathKit-Radios] Help Connecting Heath SB-610 to SB-101 for recv monitor...

[Bob Burns]

Hi 
 
I have my SB-101 on the bench at the moment doing a tidy up after having  
spent the last several days adding 160m as an additional band (not a  task for 
the faint hearted!). My SB101 is now showing the same sensitivity  and RF output 
figures as in the manual so the designers did a good job and  probably did 
not expect a forty year life!
 
1. Putting a 1pF capacitor from the anode of V4 to ground causes the S  meter 
to reduce by about half an S point from S6 using the internal calibrator  
signal - putting my fingers near to the hot end of this capacitor causes  more 
reduction in signal level. This is what I would expect and the effects of  the 
additional 1pF should be correctable by a small adjustment of the core in  T103.
 
If you are getting significant loss in sensitivity then I would check that  
the capacitor that you are using is actually 1pF and not considerably  larger.
 
The sensitivity of the SB-610 is stated to be 800mV at low frequencies so  
you will require a reasonable amount of signal in order to see it. For IF  
monitoring you need to carry out the changes shown in the manual and make sure  
that both IF tuned circuits in the SB610 tune correctly. The tuned circuit at  
the SB610 input sees the capacitance of the coax cable connecting it to the  
SB101 so keep the coax as short as possible.
 
Are you using coax inside the SB101 from the 1pF to the rear panel?
 
2. By the way, I discovered that the cores in the SB-101 RF tuned circuits  
can break very easily and I thought that this was due to weak cores. However, I 
 found that the insulated hexagonal trimming tools have shrunk a little over 
the  forty or so years and no longer fit the cores correctly, therefore 
exerting more  stress than necessary and causing the core to break. The Allen key 
that fits the  standard SB101 knobs can sometimes be used to move a jammed core 
or remove a  cracked core as it appears to be a good snug fit in the core 
center. Otherwise  you have to dig the core out with a sharp scriber without 
damaging the coil  former.
 
Anyone know of a source of newly made trimming tools for Heath  cores?
 
73

Bob 

G3OOU
G-QRP  6907
_http://members.aol.com/rfcburns_ (http://members.aol.com/rfcburns) 



   

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