[R-390] Tube questions

[Kenneth G. Gordon]

On 8 Jun 2006 at 22:28, Perry Sandeen wrote, among other things:

> Has anyone subbed the 6BY6 for the 6BE6 mixer?  If so, how did it work
> out?

Perry:

Although I have not tried this, I HAVE subbed a 6SB7Y for a 12SA7 in 
an S-41G. The 6SB7Y has about the same conversion 
transconductance as the 6BY6, as I remember it.

In the S-41G it made a tremendous difference in sensitivity, since that 
receiver is essentially the precedessor to the S-38 and the circuits are 
essentially identical. There is no RF stage.

In the R-390 I would suspect that substitution of the 6BY6 for a 6BE6 
would make very little difference since Collins designed the R-390 so 
that any noise or lack of sensitivity due to the mixer stage was 
compensated for in other ways.

I would suppose that there would be a marginally lower noise figure, 
since the RF amp stage(s) is what mostly sets that parameter.

YMMV.

Oh. I might mention that in order to sub the 6SB7Y for the 12SA7 in my 
S-41G, I had to 1) install a small filament transformer, and 2) substitute 
tubes with different filament voltages for a couple of the remaining 
tubes to make the filament string come out to 120 VAC.

Ken W7EKB