[ARC5] RF amp tubes...

[Kenneth G. Gordon]

Tonight I swapped the 12SK7s in the RF amp and the 1st IF of the 1.5 - 3 Mhz receiver I 
have been restoring with two NOS 12SH7s I bought some time ago.

The reduction in interally generated noise was amazing. I would not have thought doing this 
would have made this much difference on the 160 meter band, but it did. SSB signals I could 
just barely hear with the 12SK7s were completely readable with the 12SH7s and sounded 
twice as strong. I did have to peak up the IF stage, but the RF stage seemed to not need 
tweaking.

Tomorrow I'll measure S+N/N ratio with both sets of tubes.

The 12SK7s, by the way, are also NOS GEs. The 12SH7s are RCA.

Ken W7EKB