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Strange Behavior for New Tubes in Preamp

 A while back I had a tube get noisy in my Van Alstine T-10 RB pre-amp. It uses two of the JJE88CC and I ordered a new pair of their stock silver pin JJE88CC directly from Audio by Van Alstine. The new tubes arrived quickly and sound great and the noise (high pitched squeal) is gone. 

In the meantime I have consulted the AVA website and this pre-amp can also use: 6922,  ECC88, 6DJ8, 6CG7, and 6N1P tubes. I confirmed these numbers with someone at AVA and they said that using these numbers will not void my warranty, as long as they are 6 volt tubes.   After some research and asking questions I ordered a balanced and matched pair of JJE88CC Gold Pins, a pair of 6922, and a pair of matched 6N1P Voshkod Rockets. 

I used an interdental brush dipped in CAIG D5 cleaner, then tapped to remove excess to clean the tube sockets, even though my preamp is just shy of a year old. I install the Gold Pin JJE88CC and wait as they warm up. This is when things get weird. As they are warming up the slight noise (that sounds like steady static) gets louder and louder. At first I have to put my ear to the speakers to hear it but after 20 seconds I can hear the noise in my listening position eight feet away. It increases in volume each second until I shut off the preamp. This is with the preamp volume turned completely down. I thought maybe there was D5 cleaner residue causing trouble in or near the sockets but I had carefully used a blower and thought I did a good job removing residual cleaner.  So I re-installed the stock JJE88CC tubes I received from AVA and everything sounds like normal. Normal has been a slight static noise with my ear close to the speakers.

Today, after a week of using the same stock JJE88CC tubes, I try again the new Gold Pin JJE88CC tubes and same thing.... with the preamp volume turned clear down the noise starts out barely audible but builds until it can be heard across the room... at which time I shut off the preamp.  I let the tubes cool and remove them. I install the new Voshkod Rocket 6N1P and they sound great with the normal hiss that I'm used to if I put my ear to the speakers.

I let the preamp cool and replace the two 6N1P with the two new 6922. Same increasing loud noise but sounds more like a slightly crackly static instead of a steady monotone static or hiss.

I'm fairly new to tubes so I hope you folks have some ideas why it effects just the gold pin JJ and the 6922. Thanks.

foamcutter
larsman's avatar
larsman
3,160 posts
 

No idea why, but tubes can be strange; I got a pair of NOS 6SN7's a few weeks ago; they played fine in my preamp for awhile, and then I started getting really loud staticy, crunchy noises and then what sounded like gunshots or something heavy falling from a height. I turned off the power amp right away. I know the problem is not in the preamp as I have 2 different 6SN7 preamps, and while the noises were different, they were still loud and scary in both. I've got a pair of Ray Reserve 6SN7's, and they play just fine in both preamps. I sent those other tubes back, and the replacements had the same issue; must have been a bad batch of NOS. 

nwres's avatar
nwres
287 posts
 

Seems like the gold pin tubes and the 6922's are just bad tubes or for some reason are not playing well with the circuit. It happens, trial and error can be part of the tube game. I have had great luck buying NOS E88CC Amperex tubes from Brent Jesse and other sources and you may find the sound of the older tubes to be better than the new JJ's. YMMV.  And if they don't work out you can return them. Best of luck.

billpete
396 posts
 

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. 

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