[ARC5] Hacked ARC-5s at 10 meters - more

[Kenneth G. Gordon]

All this discussion brings up in my mind another question: it has been 
suggested that when the 12SK7s are replaced with 12SG7s, the overall 
internally generated noise level drops significantly.

I have tried this, and found it to be true for frequencies at 6 MHz and above, 
but that it really didn't do much at MF or even on 80 meters.

As I have repeatedly said, as far as I'm concerned, the primary source of 
receiver noise is that damned 12K8 mixer, which Terman's lists as the very 
noisiest mixer tube in his list at an ENR of 280,000 ohms.

However, in reviewing the characteristics of the 12SK7 and the 12SG7, there 
are noticeable differences.

For one thing, when I use a 12SG7 in the RF amp, in most cases, I can no 
longer peak the antenna trimmer: it is swung way over at one limit and 
obviously needs to go further.

Does anyone know what minor changes in biasing, let's say, that one would 
do to correct this?

Ken W7EKB
Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   Wayne