[ARC5] The "new" MF band.

Sat Sep 16 12:02:03 EDT 2017

I, along with some others, have been using a refurbished BC-453 on that band for receiving. 
I couple mine to my computer which has various pieces of software on it.

The BC-453 and the R-23*/ARC-5s work very, very well there. 

There are some modes being used on that band which require very high stability, and the 
"ARC-5" receivers, although they are quite stable already, can be improved by using 
regulated DC on the filaments.

As to whether or not the resultant stability is sufficient for those modes remains to be seen, 
however.

Of course, regulated B+ must be used too. In addition, that B+ should be kept "low". As I 
have mentioned here before, a B+ voltage of around 170 VDC appears to be the optimum.

Even the small variations in line voltage cause obvious instabilities due to the changes in 
filament voltage with some of those high stability modes.

If you decide to use the lower B+, it is a good idea to move the screen voltage feed from the 
original midpoint of the two filament voltage divider resistors to the hot end, increasing the 
screen voltage to a point closer to that required by the tubes' specification. 

Too low screen voltage causes a significant worsening of overall sensitivity.

Measured MDS sensitivity for my refurbished "ARC-5s" is 0.1 microvolt on that band.

Ken W7EKB

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