[Boatanchors] Hallicrafters SX-28 and 6SB7Y

[Drew Papanek]

Hi All,

I assume that the 6SB7Y would be a good swap for the 
conventionally-connected not-self-oscillating 6SA7mixer in the Hallicrafters 
SX-28.  It would give increased gain and maybe lower noise.  Perhaps some 
peaking of the mixer input tuned circuits would be required.

The SX-28 uses a separate L.O.; it is a triode-connected 6SA7 (all grids 
except g1 connected to the plate).  Would there be any advantage to using a 
6SBY7 there, too?  I'm thinking not; the added gain wouldn't make a 
difference in a oscillator (might not have added gain connected as a triode 
anyway).  Same noise performance there?

Stretching things a bit further, I would suppose that the first IF, which is 
a 6L7 pentagrid tube gated by the noise blanker circuit, could be rewired to 
use a 6SA7/6SB7Y.  But the Hallicrafters engineers must've had a reason for 
using the 6L7 (has a grid cap) instead of the 6SA7.

Drew

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