[Heath] SB-101 Remaining Issues

[G3OOU at aol.com]

Hi Ken
 
I have looked through all of my SB-101 related documents and in the end I  
have followed what was done in the SB-102 in relation to V3 dissipation by  
changing the screen feed from 22K to 33K. This brings the overall 
dissipation  (anode and screen) in the valve down to 3.2W and still allows the S meter 
zero  to function correctly with the SB-101 resistor values although I have 
changed  the zero pot for a spare as the old track was unreliable.
 
The overall sensitivity on 7MHz is 12dB S/N for 0.5uV at 1KHz audio signal  
with a 6HS6 in the RF stage and a 6AH6 in the mixer position to maintain 
the  heater balance as you suggested. The measured dissipations for both the 
new Rx  RF and mixer stages are well within the valve specs so no component 
changes  needed. Yet to do a full realignment of the band circuits with the 
new valves so  may gain a little more.
 
I have a 5dB peak in the Rx HF end of the passband which I have yet to  
resolve, although I did replace the 2K filter matching resistors as the old 
ones  were nearly 3K so this could be a crystal filter problem or something 
wrong in  the audio system.
 
I would like to lower the heat generated by the audio output stage a bit  
but still thinking that one through. Tx seems OK so far.
 
Getting there slowly.
 
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
Secretary of Crystal Palace Radio & Electronics Club: _www.g3oou.co.uk_ 
(http://www.g3oou.co.uk/) 
Technical web site: _www.qsl.net/g3oou_ (http://www.qsl.net/g3oou) 
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