Concept:
Some models of the GE Mastr II (type) receiver front-end helical resonator castings lose tuning and sensitivity.
These problems could also occur in Delta, Exec II, and Custom MVP style radio sets as well.

Problem 1; RF Conductivity - Tuning Screws:  In some Mastr II (style) castings, the helical tuning threads may have lost their ability for good RF electrical contact with the casting.  Why? Only the surface of the casting is conductive (RF wise).  If the locking nuts on top of the casting have severely chewed into the casting metal under the surface, the tuning screws may have lost RF conductivity.

Solution to Problem 1:  Remove the original locking nut with the teeth. Remove the tuning screw and lubricate it with electrical contact grease like those sold under the name of Penatrox, Noalox, etc. Replace the tuning screw.  Place a split lock washer *not a star washer with teeth* over the threaded tuning screw. Place a a stainless steel hex nut on the adjustment screw and secure it to provide just enough tension to keep it from moving.  The use of a wrench or pliers to hold the lock nut may be needed while readjusting the helical screw.

Problem 2, Growing Tin Whiskers:  Receiver front end castings with a shiny appearance, made before approximately 1983 *may* exhibit these problems:
Tiny tin whiskers growing inside casting walls may short out the coil or tuning capacitor. The whiskers may be difficult to to see without magnification, but disassembling the casting will reveal their existence if present.   The whiskers may appear to be slightly greenish in color.   They are created *possibly* because of a reaction of the plating metals with the atmosphere.   The picture below was taken of a 1977 GE Mastr II VHF helical casting.

Solution to Problem 2:  Adjust the helical tuning screws all the way to the top (screws sticking out of casting).  With a cleaning spray that leaves no residue (NOT lubricated tuner cleaner, use chemical 111 or the like), wash the inside of the helical resonator cavity. A small brush or cotton swab may be helpful.   After thoroughly drying the interior of the helical casting, coat the interior cavity walls, coil and tuning capacitor with a coat or two of clear lacquer or enamel spray.   Krylon or other brands will work.   This step is to try and seal the surface from interaction with the atmosphere.   If the bottom cover is shiny and shows whiskers, treat it the same way.

CAUTIONS:

1.  Chemical 111 is a very nasty solvent, so handle it as directed.  111 is found in solvents like soldering Flux Remover.
2.  Be careful not to damage the tuning capacitor when adjusting it all the way to the top of the casting.   Do Not force the adjustment.

NASA and other satelite operators are very concerned about the "tin whisker" problem as several satelites have been lost due to electronics failures that have been traced to whiskers.   See The NASA Tin Whisker Web Site.

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Picture of the whisker growing was provided by Tracy Hooker KA5ECS.
Original Author has ask to remain anonymous
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