[MRCA] PRC-47 Meter Fixed

[n1jzv at midmaine.com]

I posted earlier looking for a PRC-47 rf transformer "T101", ended up
sourcing one from Fair radio.
  Symtom,the meter would only indicate above 7MHz and just barely.  The
radio is a depot rebuld from Albany,GA and appears unused since rebuild.
 I sent my order in to Fair with a picture of T101 just to make sure
they knew what I needed.  Phil at Fair called and said yes we have one
but I have never seen one like yours.  All he had seen were of a round
style and mine is a cube.  It arrived, was installed and now all is fine
with the meter circuit.  I am attaching an email from a fellow MRCA
member who is working on the radio.   I thought other PRC-47 owners may
find it interesting.

On examining the T101 that was in the set, it's a bit of a mystery. It's
clearly a professionally made piece machined out of a piece of nylon or
delrin. All the solder connections had red inspection lacquer on them so it
was most likely installed at the overhaul depot. My best guess is that it
was an attempt to reverse engineer the original Collin's part perhaps when
they were no longer available from Collins. Whoever designed the part did
not understand the original part and got it completely wrong. The piece
contained a small J.W. Miller type miniature inductor with the RF output
wire passing near it. At best you might get a very small coupling effect
from stray capacitance but that's all. Again my best guess is that someone
simply measured the inductance of the winding on the Collin's part and used
an inductor of that value. What they did not understand was that the
original part was an RF transformer wound on a toroid core and depended on
the unique characteristics of a toroid. The RF output lead passing through
the center of the core is a one turn winding that couples to the windings
around the core.

As this substitute piece was designed it could never function as the
original Collin's part did, Your output meter did not work by design and no
amount of troubleshooting would ever make it work. I wonder how many other
47's are out there with this part in them. It certainly is one of the most
unusual things I've ever seen.

Mark
K1HF

Happy Thanksgiving