[Milsurplus] Low B+: The Genius of A.R.C.

[Bruce Gentry]

Ray Fantini wrote:
> Not being critical because I have not done the work myself and have no experience using octal remote cutoff pentodes at low voltages but have to wonder why other then the convenience of having 24 or 28 volts there why you use such a low voltage?  Looking at the plate characteristics curves of the 12SK7 the tube appears to perform rather poorly below 40 to 50 volts and almost at the point of having no plate current at 20 volts. 
>   
   The ARN-6 uses the 12SK7 and other common 12 volt tubes with  24 
volts on the plate. The tube complement and general design are close to 
theARN-7 that uses about 220 volts on the plates. The big difference is 
the audio output, the ARN-6 uses two 26A7s in push pull paralell instead 
of a single 12A6 in the ARN-7.  The ARN-7 has far higher audio output 
and sounds far better to my ears. I also think the 26A6 used in the 
R-392 is just a 6BA6 with a 24 volt filament.  I wonder if the tube 
manuals just didn't bother to plot  operation at what they considered 
foolishly low voltages nobody would ever use.  This is all rather 
fascinating, how tubes were used on transistor voltages at the dawn of 
that technology.

    Bruce Gentry,     KA2IVY