Quote:
Originally Posted by Tom Albrecht
I've also noticed that on the 621, if the shield is missing from the 6AL5 FM detector, the sound is very unstable and has all kinds of problems.
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Also if the set uses the center connector (if present) on the 6AL5 FM Det tube socket as a tie point, verify that they trimmed the leads off and a wire does not protrude through the topside of the socket and keep the tube from properly seating. The older 6AL5's had a larger recess in the base than the modern ones.
For a general audio or visual microphonic problem, simply tap on each and every tube gently with an insulated stick from the top of the chassis.
If that narrows down the search area, try gently tapping each resistor and capacitor in the same general area underneath the chassis.
If tapping about the volume control changes the problem, consider cleaning the control.
Coating the pins of a suspect tube with contact cleaner and inserting and removing a few times will clean them. Wait long enough for the cleaner to dry before turning the set back on.
James