[AMRadio] R-388 PTO ALignment questions

John Lawson jpl15 at panix.com
Sun Feb 5 13:31:20 EST 2006

   Well, I found and fixed the problem with my R-388 PTO - C008, the .001 
feedback capacitor, had shorted. It was replaced with a rather carefully 
hand-selected Orange Drop of suitable parameters. Both 6BA6s were replaced 
with NIB units, checked for proper Gm.  All ok - it's putting out a very 
spectrally-pure signal.

   I have begun the mechanical alignment process using Fred VE1FA's 
guidelines.  All is making sense except that the 'midpoint', ie. 2.5000 is 
displaced by about 150 KHtz toward the low end of the range.

   I'm able to narrow the spread between the center and the outside edges, 
but no matter what I do, the 'split' is assymetrical.  And it appears to 
be a lot more than the corrector stack would be capable of nulling out - 
it's nearly 15 degress of shaft rotation.

   So if anything 'jumps out' at y'all - do let me know. I'm quite anxious 
to get the Old Girl reassembled and back on the air.

    Now: in the grand scheme of things - if this turns out to be one of 
those tip-of-the-iceberg hundred-hours-on-the-bench type thing - then it's 
going back in the radio like it is...  it was much worse before, and I 
used it for twenty years.  This difference doesn't translate to hugely 
gross errors on the dial, and it's livable as-is currently.


John  KB6SCO

More information about the AMRadio mailing list

This page last updated 17 Feb 2018.