[Heath] More SB-200 joys...

[Kenneth G. Gordon]

On 14 Jan 2012 at 14:08, G3OOU at aol.com wrote:

> Hi Ken

Hello, Bob. Long time no hear from. :-)
 
> Thanks for the update on the SB200 work.

I have more coming yet....

> Changed the Rx RF stage to a 6HS6 which increased the sensitivity
> somewhat  but not surprised as the slope is almost twice that of the
> 6AU6 - will not  help with the dynamic range though as 40m is very
> busy in the evenings with 
>  large BC signals. The heaters also needed re-balancing as the 6HS6
>  takes  
> 450mA which is 150mA more than the 6AU6.

If you change BOTH the RF amp and the first receiver mixer to the 
6HS6, you will find you will not need to rebalance the filament 
string as those two tubes are on opposite sides and thus the balance 
remains correct.

As the 6HS6 is getting very difficult to find, I use 6AH6s. Those are 
only slightly less "high-slope" than the 6HS6, are much more rugged, 
and a LOT cheaper and easier to find.

The filament balance issue will occurr with the 6AH6 also, so change 
both tubes.

BTW, I have always thoroughly enjoyed your work on the Heathkit rigs. 
You are a real master at it. I always find some really innovative 
thinking on your part. :-)

vy 73.

Ken W7EKB