Why does unplugging/replugging TT leads from tube phono pre-amp reset dead channel?

Good news?   I have not been able to replicate the issue of late.  Perhaps this post will remedy that. I've ordered from Amazon a tube of DeOxit. Just in cast that's the culprit.  Next steps are to check loading on cartridge.  Suggestions on loading to address this issue? It sounds fine as it's currently set.  Also...will be interested in seeing what else I discover with the hood open. 
Lewm- The male RCAs from Linn simply screw open- very easy. How do I know by visual inspection if there is "an intermittent or cold solder joint to the hot pin."  I'm not sure what that means. Thanks. 
Thanks all.  

As expected...it couldn't last.  So the left channel dropped after a loud passage on Chet Baker's Chet. Great morning tunes.  I spun the plug.  Wiggled it.  Wiggled near the TT. Nothing. Pulled and replaced.  Channel returned.  I visually inspected the insides of the plugs...the solders look solid.  A bit of oxidation inside the ground part (inside the outer part).  
Thanks for sticking with me on this. 

Joe

I'd be surprised if the problem isn't resolved after a good cleaning of all connectors from the cartridge pins to the RCAs.

Jmfawdofile 12-22-2017
Suggestions on loading to address this issue? It sounds fine as it’s currently set.

Joe, the main reason I suggested that you determine what the loading is set to is that it might help in determining the cause of the problem. I’m doubtful that any change you might make to the setting would constitute a solution, although I suppose it’s possible.

My original point regarding loading was that when you disconnect and reconnect the cables you are not only physically manipulating the cables and connectors, but in addition when the cables are disconnected you are temporarily changing the impedance presented to the input circuit of the phono stage from a very low value (essentially the cartridge’s impedance) to a significantly higher value (whatever the loading is set to). And it seems conceivable to me that doing so might be allowing the input stage to recover from some abnormal condition.

As you can see in the manual resistive loading is set at the factory to 47K, but DIP switches are provided in the unit which can put resistors of 100 ohms, 1K, and 10K in parallel with the 47K, in any combination. There is also provision for paralleling a resistor supplied by the user, which a previous owner may have done if you are not the original purchaser.

So the overall load resistance may be somewhat less than 100 ohms, or it can be as high as 47K, or it can be at various settings in between. If it is at the low end of that range, the likelihood that my hypothesis accounts for the problem is minimal, since whether or not the cables are connected would make a relatively small difference in the impedance presented to the input stage. If it is at the other extreme, 47K, the likelihood of my hypothesis being relevant would be significantly greater.

But to answer your question, if there is any possibility that changing the loading might be a solution, my guess is that the 47K setting would stand the best chance, if it is not already set that way. If it is not already set that way, changing to 47K would change the impedance presented to the input stage during normal operation in the same direction (i.e., making it higher) as disconnecting the cables has been doing, albeit to a smaller degree.

Good luck. Regards,
-- Al

No advice, only a comment. I’m surprised that when mentioned your TT was an LP12, that everyone didn’t  immediately blame the TT. I have an LP12 and just it’s mention seems to bring out all sorts of haters. It’s gotten comical. Seriously, good luck resolving your issue.