[Heath] SB-101 Remaining Issues

[Robert Groh]

Bob,

Greatly enjoyed your attention to detail and good engineering sense!  Keep us up 
to date!

Bob Groh, WA2CKY
'old timer and radio designer'




________________________________
From: "G3OOU at aol.com" <G3OOU at aol.com>
To: kgordon2006 at frontier.com; heath at puck.nether.net
Sent: Tue, January 17, 2012 4:09:22 PM
Subject: [Heath] SB-101 Remaining Issues

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
Technical web site: www.qsl.net/g3oou
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