heathkit part # 40-1653

[John A Diefenbach, K1TLV]

Boy!! This is the kind of stuff I like to see in this reflector...a way to improve on something that was 'okay' early on but (maybe) not good enough. Maybe the Heath Company might have improved on the original design but we'll never know.
> 
> From: Chris Iwata <ChrisIwata at AOL.COM>
> Date: 2007/02/14 Wed PM 06:54:26 CST
> To: HEATH at LISTSERV.TEMPE.GOV
> Subject: Re: heathkit part # 40-1653
> 
>  
> In a message dated 2/14/2007 3:39:15 P.M. Pacific Standard Time,  
> mgrandy at TELUS.NET writes:
> 
> Looking  for Heathkit part # 40-1653. This is a 6.8 micro H peaking coil used 
> on the  "C" board (L323) SB-104A. Is this available anywhere or a suitable  
> replacement. I have checked several sources on the internet with no  luck.
> Murray (VE7MGY)
> 
> 
> 
> This coil is Heathkit's attempt to boost the output of Q305 on 15 and 10  
> meters as the peaking coil is somewhat resonant around these freqs. But,  I've 
> found mostly this makes the stage unstable.  Ever notice how if the  housing 
> around this transistor is not grounded just right by those brass spring  clips 
> the rig does strange things on 10 meters?!  
>  
> A better solution is to re-design the Q305 stage as a broadband  amp (like 
> Q304).  Change L323 to 5 turns on a FB37-43 ferrite core. Add  shunt feedback by 
> connecting  680 ohm resistor and 0.1uF ceramic  in series between base and 
> collector of Q305  (in the same fashion as R301  and C301 on Q304). Change R309 
> to 4.7 ohms to realize a little more gain to  combat the feedback and change 
> C308 to 0.1uF. These mods make the stage more  stable and also provides more 
> even output for ALL bands and makes Q305 a more  consistent source for the 
> subsequent band pass filters. All because of the  feedback. If you can't find the 
> core, swipe a ferrite bead from another board  (Counter board has way too many) 
> and run 4 turns through it, that's what I  did.  These ferrite beads are 
> similar to FB43-301.  If your  transmitter output is running a bit low from these 
> mods, lower the value of  R318 to compensate.
>  
> If you are a purist who thinks Heathkit design was golden, I might  have the 
> peaking coil laying around somewhere. If you want to go this route  get back 
> to me, but before that try substituting a ferrite core or ferrite bead  for 
> L323. This alone may be sufficient, and actually either one is better  than the 
> original peaking coil anyway  ...
>  
> Chris, KL7DM.
>  
>    
> 
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