[R-390] Intermittent Noisy Drop In Gain, With Fix

[David Wise]

When I was finishing up measuring mechanical filter voltage and impedance, my '54 Motorola started cutting out.  That is, there was an intermittent noisy drop in gain.  It came and went when I moved V501.



The bottom side of XV501 is bisected by a bulkhead that doubles as a shield, with terminals 1, 2, and 7 on one side, and 3, 4, 5, and 6 on the other.  The pin 6 (screen grid) terminal has a plastic sleeve to prevent contact with the shield.  When the deck was assembled, the shield was bolted in off-center and pressing against the sleeve.  After six decades, the sleeve broke down.



I had some creep-resistant plastic insulation scavenged from a solid-state fluorescent ballast.  Rather than disassemble half the deck to get to the bolts, I cut a strip, quadrupled it, shoved it between the terminal and the shield, and glued it in place.  Should be okay for another 60 years.  :)



Dave Wise