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Chasing down the problem

Couple of nights ago, I was listening to my mono block tube amps and after about ten minutes the right channel goes silent! What the heck!! So begins the search for the culprit...is it upstream of the amps, or is it the right side mono block that has an issue...and what kind of issue.
Luckily, I own another stereo ss amp, so the first thing to do was to hook that up and see if the problem continued. This would eliminate a few pieces of gear as the culprit...basically everything in front of the tube mono blocks...except the connection from the preamp to the mono blocks...the ic’s.
The system played fine with the stereo ss amp in the chain...therefore leading me to believe that the following components were not at fault...1) the front end digital player and the front end turntable set up ( I did play both to be certain) 2) the tube preamp, 3) the connections between these components...speaker cable and ic’s ( I use different ic’s and sc’s to connect the preamp to the ss amp than with the tube amps).
The next day, I hooked up the tube mono blocks again...and this time after making sure that the connections at the amps were tight and that the tubes were all re-seated. Music played again in both channels ---for about twenty minutes! Then the same issue reared its head again, the right channel was silent. Hmm.

Therefore, unless I am wrong, the only two possibilities left are the right tube mono block...or the right ic feeding that mono block from the preamp. My next thing to do was to change the ic’s for another pair ( could have swapped left for right, but since I have other pairs of ic’s that i know are good, i figured why not try this next) Plan being to check the ic’s and then finally start to move tubes from one mono block to the other and vice versa to see if the issue changed channel.
Last night I listened to the same set up but with just the ic’s changed out between the amps and the preamp....and no problem. ( this after a two hour session).
Hopefully, I have identified the issue..would seem that the original right side ic has a iffy connection somewhere ( a lot easier to address than to have to get the mono amp worked on).
Anyone else have a problem like this that took a little ’work’ to identify?

128x128daveyf
daveyf's avatar
daveyf OP
2,877 posts
 
Well, the problem is back...and this with different ic's. So, I am guessing that at this point that the ic is not the issue. Next step is to swap the left side driver tube on the left side mono block to the right side mono block and vice versa to see if the issue goes to the other channel. Stay tuned.
BTW, could a driver tube failure cause a cessation of sound? Seems a little odd, but onwards I go.
paulcreed
564 posts
 
Have you tried pushing up from up under the RCA connector at the input of the amp or output of the preamp? I had this problem long ago on a BAT amp. I had to keep constant upward pressure on the RCA which meant I had to place a wood block under the RCA. Maybe not the best solution but it worked.

daveyf's avatar
daveyf OP
2,877 posts
 
@paulcreed Thanks. Yes, I tried that and the problem still persists.
I swapped one of the driver tubes to the other mono block and vice versa...still problem persists. Tomorrow, after the amp has cooled down again, I will swap the other driver tube and try again. ( The amps employ one 12au7 and one 12ax7 per channel as driver tubes. The 12ax7 swap is next.) If that still doesn't expose the issue, then it will be replacing the power tubes....in my case four KT 150's...and if that still isn't the issue...well then she's off to the repair shop..:0(
jetter
3,035 posts
 
daveyf, a couple of questions. Why don't you just swap all the mono block tubes at once so you can confirm or eliminate a tube problem in one shot?  Are you using a SS or tube preamp, and if a tube pre amp when you hooked up your SS amp did you give it enough time that if it is a preamp problem it would show itself?
daveyf's avatar
daveyf OP
2,877 posts
 
@jetter  Thanks for the suggestions. I did play the preamp with the ss amp for a few hours.Nothing showed up, so I am assuming that the preamp is ok. As a last resort, I will hook up the ss amp again and give it a very long test to see if the problem rears up again. As to replacing all of the tubes at the same time in the amps...I thought about this, but it wouldn't tell me which tube is the culprit if I did that...just that it is a tube problem in the amp. So, I am doing one set at a time, from left to right and vice versa. This is more time consuming, but should zero in on the particular tube if it is the issue. Lastly, i was thinking to swap my speakers over...left to right, as it is maybe possible that a x-over part is overheating, although I doubt this as the issue was not present when I used the ss amp. Nonetheless, it is easy to check...and it will be the last thing on my list before sending the amp for repair. Onwards--
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