Howdy Steve,
Socket corrosion can be a problem, but often these intermittents are caused by improper tube removal technique. Few people today are aware that removing a loctal tube from its socket must be done in a specific manner to avoid damaging both tube and socket. The typical practice of pulling the tube vertically from the socket while wiggling it around is incorrect. This causes permanent damage to the socket locking mechanism and causes the familiar looseness and intermittent problems you describe. It can also break the tube seals.
The metal loctal tube base features a small "bump". The tube should be carefully tilted slightly in the direction of the bump and pulled from the socket while tilted. Only modest force should be needed to extract the tube.
Loctal tubes rely on the locking action of the base to hold them in place. Once the damage is done the tube may not remain properly seated and intermittents set in. Sometimes the only solution is to replace the socket. So many have been trashed over the years that it can be difficult to find good replacements...
73,
John K9WT
I've seen a lot of early two-way radios from Motorola that used the loctal tubes.
Loctals were also used in quite a few models of commercial table- and portable-broadcast receivers.
My experience with repairing/restoring broadcast and shortwave radios that used loctals is that about 25% of the tubes/sockets become troublesome (at least one bad pin-to-socket connection in a quarter of the tubes). The result is a lot of wiggling of tubes in their sockets trying to get stable operation. Deoxit helps but is not a complete answer to this particular problem.
I've always wondered if the choice of metals or plating for the pins and/or the socket contacts is the problem. Maybe dissimilar metals touching for years creates a difficult corrosion issue?
The loctal pins look like the same sort that were used in 7 and 9 pin miniature tubes but maybe the socket contacts are different? I recall the loctals look like like they have less contact area and are like scissors biting the pin whereas the miniatures' socket contacts are wiping the pings with longer springy tabs.
Steve WD8DAS
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