[R-390] Inexpensive Nuvistor Tube Mod

[Perry Sandeen]

A while back several members were looking at using the dual 6DS4  nuvistor mod for the R390a and
SP-600.  The nuvistors are in the range of $15-$25 a piece making it a an expensive experiment.

The website posting the schematic suggested using the dual triode 7963 "peanut tube".  I found a
website for SND Tube Sales in MO who sells them for $4 each.  All the info for the tube can be
found at: the WA2ISE sub-miniature tube page.  The short specs are: 7963 twin triode 8DG h: 6.3,
0.35a Rk=270 mu=40 p:100v, 7.5ma gm=13000 Rp=3100 ... 

If one can get a 7 pin header, this combination may prove to be a cheap performance enhancement. 
The site does mention that for the SP 600 one needs to do some aligning.  This is also true if one
uses a 6BZ6 sub for the 6BA6 and want optimum performance.  Regards, Perrier


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