[R-390] My 'new' '67 EAC is now "on line" 8^) Ballast Tube question.

Wed, 16 Jul 2003 19:31:23 -0000

Well, to reassure myself and others who have expressed concern I borrowed
some tubes from another receiver here (my homebrewed longwave beacon set)
and subbed both the PTO and BFO tubes at the same time (and yes, they are
6BA6's, not 3BA6's 8^).  No change, the ballast glows the same.  I've just
come to the conclusion that this one may be drawing close to the end of its
lifespan.  I can't find it in my archives, but I KNOW I read somewhere in
the past that is an indicator that either the ballast tube filament is
getting "thin" (worn out) OR that possibly the inert gas has leaked out of
it around the seals. 

I also tightened up the ground screws on the applicable tubes, though I
would suspect that a loose one would open up the filament line or at least
present a high impedance that would actually REDUCE current rather than
increase it.

73 de Phil, KO6BB
DX begins at the noise floor!
[email protected]
Merced, California
37.18N  120.29W  CM97sh

-----Original Message-----

Phil,

    Experience has shown that the filament of the ballast tube SHOULD 
only partly glow when all is well.  The symptoms you describe SHOULD 
mean that the circuit that it regulates is drawing too much current.  
Either one of the tubes has some form of a short, or something else is 
causing excessive current draw.

    It's probably going to be painful to track down, but will be worth 
it in the long run.  As mentioned in an earlier post, if the PTO tube 
came from the same lot, it could be a bad lot.

    Try swapping the two tubes that R510 regulates from another R-390A.  
If the ballast tube goes down in brightness, then one or both of them 
are problem children.  IF NOT, then something else is awry.  Perhaps a 
bad or flaky ground.  These radios are notorious for this with the MFP 
coating

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