[R-390] RE: 3TF7 resistor replacement

[Drew Papanek]

Charles B. wrote:

>Can some one give me the specifics on how to replace the
>3tf7 Ballast tube with a 42 OHM resistor? <snip>

Bob Camp responded:

>Alternately you can solder the resistor to the tube socket pins under
>the IF module.<snipped>

That is neat and unobtrusive, but will add almost 4 watts of heat under the 
IF module.  Baked BFO, anyone?

Bruce MacLellan responded:

>I had a ballast fail on me last night.    I  replaced it with two
>51 ohm  resistors in parallel inserted into #2 and #7 socket positions,
>Use 2 watt or better.     A bit of shrink tubing on the leads will keep
>them away from the socket shield mount.      If you don't have carbon you
>can get MOV s in 3 and 5 watt values from Mouser.<snip>

Two 51 ohm resistors in parallel is about 25 ohms;  that value is too low.  
The desired
value is 42 ohms.  A 47 ohm resistor will work.  A sufficient power rating 
is 5 watts; a 10 watt
unit would run cooler and be less of a tempation on which to burn your 
fingers.

Bruce wrote of "MOV's" from Mouser, I believe he meant "MOX" ( metal oxide 
power resistor).

Methinks the simplest ballasubstitution to be swapping out the PTO and BFO 
tubes with 12BA6, then  jumper out the ballasocket.  No resistor required!

An Alfred E. Neuman impostor attempted to kick the beehive by writing:

>I have heard from various experts that if one were to do this, when  
>somebody
>turns a light switch on in any part of the house, the receiver will  change
>frequencies. Can you confirm or deny this?

In this rushing-about-hither-and-thither busy busy busy age many of us just 
don't have sufficient time
and energy to kick about a good ol' dead horse and play the controversies.   
Wei-i Li has recognized that unfortunate hallmark of present-day life and 
has given us powerful freeze-dried knowledge comprising tidbits coursing 
through this forum over the years, complete with all of the high-spirited 
equine percussion for which one could ask.   Goto r-390a.net     , click on 
references, Pearls of Wisdom, Ballast Tube (then just add water).

Drew