[ARC5] 10 meter BC-454 a bit more

[Kenneth G. Gordon]

With the 12SG7 installed in the RF amp, I can still hear a 0.1 microvolt signal in CW, 
although it is right at the noise level, even through the loudspeaker.

With headphones, a 0.5 microvolt signal would be fully copyable in CW.

With the 12SK7 installed, I need 0.5 microvolts to be able to hear it in CW through the 
speaker. I need at least a full microvolt to copy the signal with headphones. Obviously, the 
tube-generated noise is masking the signal.

Ken W7EKB