[R-390] Nuvistaplug?

[Mark Huss]

Here is one for all the experts.  A plug-in modification for SP-600's 
was the Nuvistaplug.  This was a replacement for the first RF amplifier 
in SP-600 that substituted a pair of 6DS4's in a cascode circuit.  The 
resulting 6 to 9 dB increase in Signal to Noise level made the SP-600 
sound like a new receiver.  My brother recalls that there was a similar 
modification using a 6CW4 for the R-390A, popular with MARS operators.  
I happened across the schematic today, and it looks like with changing 
one pin in the Nuvistaplug, you could drop in the replacement for the 
6DC6.  This should increase the signal to noise level of the first RF 
Amp.  So has anybody even heard of this being attempted?