Strange Behavior for New Tubes in Preamp

I've been having a similar problem lately. I can't decide if it's tubes or a bad connection at the speakers. I roll tubes often, trying different combinations of 6sn7's. My preamp uses 4. I recently upgraded speaker cables to Blue Jean Canare and have had some issues with connections. I had them made with spades at the speaker end and locking banana at the amp end. I had trouble keeping the spades tight at the speaker end. The spades are very large and very smooth/slick/slippery. I had them spin around and contact each other which made quite a noise. I have since connected the spades to my amps and they stay tight and can't possibly touch. I've had some issues at the speaker end with loosening of the locking bananas. They are an odd fit to the old AR9 binding posts and I do have one loose binding post. 

After the switch of bananas to speaker end, I started to hear popping and crackling again, not the terrible loud problem I had before but similar. Not a dead short but possible loss of connection. Still sorting out if it's a tube issue or a cable/speaker connection issue. I got through a few hours of listening with no problems before it started for the second time. Each time has been with GE/KenRad 6sn7 side getter tubes, two different sets. No idea if they are the problem yet or not. Testing is making me more nervous with each problem that occurs. Anyway, will post if I figure it out. I have another pair of speakers to try also, which might help. I wouldn't think one loose binding post could be so much trouble but maybe it could. 

I've had tubes make loud horrendous noises when brand new. I disconnect my preamp and let the tubes cook for 8-10 hours. Then shut it down and try again in an hour. That's worked before. 

But I've also had to do the "Tapping Treatment" from Brent Jesse and saved a pair of Sylvania 6SN7s I thought were toast. 

In the Link Read the Post from 'pindac'

I have had Brand New Matched Tubes from modern production measured after receiving and the data produced was very very different to what I was informed I was to be supplied.

My Tester friend advised the Tubes should not be used as Amp Damage could be the result.

I took that advice and also got a full refund.

Do not do anything that might be damaging the Amp', pursuing the use of the Valves is not advised. Hold off on using the Valves and take the initiative to return them for a refund, there is nothing to lose, and any user of Valves should brace themselves as this could be a more than one occasion scenario

I myself have returned many Valves for a refund due to poor measurements discovered against the sales advertised condition info.

https://forum.audiogon.com/discussions/who-is-your-favorite-tube-seller

I would never use D5 in a tube socket (or anything that "coats").

This said, sounds like a bad tube.

Had a "contact" problem with  JJ 2A3's years ago and discovered that the pins were slightly smaller than the norm.

DeKay

Since you try different tubes that are almost the same but not identical, have you measured the voltage coming from the grid.  For example e88cc does not like more than 90 volt or less than 85 as for 6n1p they might like something around 100 volt but not less than 95 . Take the numbers with a pinch of salt and read the manufacturers recommendations to be shore 

Next is the current draw from the heaters , have the voltage regulator enough amps to heat the different tubes ?