[R-390] 3TF7 vs 3TF4

[Dave Merrill]

There is a good discussion of the 3TF7 vs 3TF4 in the 'pearls'

http://www.r-390a.net/Pearls/ballast-tube.pdf

>
>Hi Phil, Ed & List
>
>The last time it came up, I recall that word was that the 
3TF4 was not a
>good sub -- resistance is something like double or triple 
that of the 3TF7
>and would not be long-lasting.  However, in some contacts 
here and there I
>came across someone who has used them and says "no problem".
>
>What about this?:
>
>What if you put a resistor in parallel with a 3TF4 of the 
right value to get
>the filament voltage up a notch and take some of the current 
off the ballast
>tube to reduce glow and increase life?
>
>Would there still be some ballast action with the 
combination?  Might be a
>bit tricky to install alongside the tube.  The resistor 
probably should not
>be inside the module chassis.
>
>Any thoughts on this?
>
>Barry