[R-390] 6T4F

[Norman Ryan]

Hi, Glen,

Nice research!

I have an Amperite TJ311M01 that measures cold at 13.3 Ohms DC
resistance on my Fluke DMM 8024B.  I'm patiently waiting for it to
exhaust so I can replace it with a 3TF7.  :-)

All seriousness aside, the above ballast doesn't carry the designation
"3TF7."  Thus the FEDLOG may have assigned a different NSN when the 3TF7
appeared.  (I'm assuming 3TF7 is a newer designation for Amperite's
catalogue number TJ311M01.)

It came out of a spare IF deck.  I'm too lazy to pull my working R-390A
out of its case to do voltage checks and substitution with a 3TF7 to see
if the regulated tubes are getting similar voltage, but expect it's
close enough for government work.

The lettering is that notorious stuff that wipes off easily.  I couldn't
make out that any lettering is gone.  What's there is is there-- that
is, no smudges.

Hope this helps.

73 de Norman KG4SWM


Glen Galati wrote in part:
> 
> Here is some interesting info on the the 3TF7 Current Limiting Resistor as
> specified for the R-390 Series. The FEDLOG description specifically
> identifies this as Application = R-390/URR,  AC/DC, 0.040 to 0.260 Amperes,
> 10.2 Volts Threshold,  9-Pin Miniature with T-6-1/2 envelope. NSN
> 5905-00-259-1964, and was last procured $118.27. Measured DC Resistance is
> approximately 12-12.75 Ohms.
> Now, here is an interesting twist to the story.  Amperite PN: TJ311M01, NSN
> 5905-00-681-4707; DC, Current Range 0.31 to 0.33 Amperes, 8.0 Volts
> Threshold,  9-Pin Miniature with T-6-1/2 envelope. The FEDLOG states "WHEN
> EXHAUSTED USE 5905-00-259-1964" which is a 3TF7.  Hmmmmm! Makes you
> wonder-What we really need here is to do a close scrutiny of the TM/TO's for
> the R-389, R-390, R-390A. and R-391 Part List and see what part number and
> stock number was listed.