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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
atmasphere's avatar
atmasphere
11,800 posts
 
BTW, could a driver tube failure cause a cessation of sound? Seems a little odd, but onwards I go.
It certainly can!

As you've found out though, that wasn't it. Here's a bit of troubleshooting advice, should you run into a problem that occurs in one channel and not the other:

The first thing to do **always** is simply swap the interconnect cables left for right at the inputs of the amplifiers. Then run the system. Did the problem move? If yes, the amps and speakers are off the hook. If no, its in the amps or speakers.


If yes, the problem moved, then you swap the interconnect cables left for right at the output of the preamp. Did the problem move? If yes, the cables are off the hook- its in the preamp or a source. If no, its a bad cable.


In this manner you can test every component in your system and its a lot lot easier than swapping out for another amp which could potentially have its own problems, creating confusion. Intermittents like the switch in your preamp make finding the problem harder; if the system seems to work fine after a change just let it play- sooner or later the bug will raise its ugly head.


If you had followed this procedure, you would have known much sooner (probably by a day) that the preamp was the problem, and no ancillary casualties. So keep this in mind. Electronics are very hard to make completely failure proof, so knowing how to go about this can make for far less frustration- something no-one needs!
daveyf's avatar
daveyf OP
2,871 posts
 
@atmasphere Thanks Ralph. I did exactly as you recommended and followed this protocol. This is what ultimately lead me to the preamp, but in my case, since the issue was intermittent, and for some reason did not happen to show up when I changed amps, the true culprit was further hidden. To add to that, i changed the left and right interconnects at the amp and the issue followed the left to right change! This lead me ( falsely) to suspect the cables. I now believe that the way Ken Stevens has these toggle switches connected can lead to a intermittent issue with either channel, as the signal passes through all of his switches before going to the input or the output connectors. Not sure if this is typical in tube preamps, but there we have it.
atmasphere's avatar
atmasphere
11,800 posts
 
If you are referring to those toggle switches on the front panel, yes, they are very capable of doing that. It is possible to clean them a bit, by putting the preamp on its rear panel and spraying a bit of Deoxit in the green and black can directly into the crescent moon that appears under the toggle handle, then operate the switch and do it to the crescent moon on the top. Then work the switch back and forth about 20-30 times. For this operation you don't even have to remove a cover.
daveyf's avatar
daveyf OP
2,871 posts
 
Thanks again, Ralph. This is pretty much what my tech did when he received the preamp, except he did remove the top and sprayed from behind onto the offending switch. Seems to have solved the issue. When i told Ken that is what was the issue, he was not happy that Deoxit was spayed onto his gear, feels it is like salad dressing, LOL. 
mijostyn's avatar
mijostyn
8,570 posts
 
I use break cleaning fluid for that, the old chlorofluorocarbon stuff. It is pretty much the same stuff they can as electronics cleaner. 
In my experience and I do not have a lot, once a switch starts doing this it will do it again sooner and eventually fail. Atmasphere do you think this is correct? I also think it depends on the quality of the switch. There are some pretty nice switches out there now. 
So, daveyf you still might have to pull out that soldering iron:)
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