Chasing down the problem
The deal is a lot of toggles and switches in general, get a build up of worn material INSIDE the switch housing.. Different aerosoles, with different blends, do different things. BE very careful spraying brake fluid or starting fluid on ANYTHIG... Much less MEK.. and some solvents.. I've drilled hundreds of switches, sprayed, cleaned, and resealed with a dab of silicone... A LOT of crap usually comes out.. Then they work, half the time again, and half again... You can prolong the life a LONG time with maintenance.. :-) 3M (WD40), Deoxit, Liquid wrench, ALL make electronic products. I would use the correct one. One will wash and dry, one will lubricate with polymers, or petroleum. ALL should dry though... Some lubricates the contacts some lubricates the actual switch. It all wears, and leaves a mess.. Regards |
@mijostyn I was wondering about that...how long the repair will last. So far, so good. These toggle switches are still available and I have bought several replacements if needed. It is no easy task to replace them and my tech feels it would be a pain to do. So here's hoping the fix continues to last. |
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:) |
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. |
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. |
@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. |
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! |
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@daveyf , I, for one, think you did a pretty thorough job of trying to trace the problem. Unfortunately, it was something you didn't consider, nor would have I. A dodgy switch in the preamp would be one of the last places I would think to check. Though, if it were to happen to me, I would contact Ralph Karsten (atmasphere). Though I own his equipment, I do know he will help anyone in distress, as his presence on Audiogon shows.- A very nice and generous person. Bob |
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To conclude this story...I finally had to take the preamp ( yes, not the amps at all!) to the tech. It turned out it was a switch on the preamp that was not functioning well and was intermittently cutting off the right channel!! My tech diagnosed this is minutes! While I was playing with the amps, I inadvertently destroyed one of the Tele 12Au7 driver tubes and one of the KT150 power tubes went bad...but this didn't cause the problem in the OP! So, now that the preamp is up and running again, all is well. Motto of this story seems to be that for those who are less technically inclined--like myself--diagnostics isn't our strong point. |
@jetter Thanks. I will swap tubes in the preamp...left to right. But I can not see how this could be the issue as the preamp utilizes separate/different tubes for the phono stage and the line stage ( left and right channels)...and in my case, both the phono and line stage exhibit the same problem. I checked the cables, all are fine. I think it likely that this is going to be a repair for the tech. |
daveyf, I don’t have much knowledge about the inner workings of our gear like many here posses. I do know that preamp tubes last a very long time, but I would hope that you just need a new tube. This is what I would do: If you have not done so already, switch the interconnects from one preamp channel to the other and see if the problem follows the interconnect to the other channel. If no luck, with the preamp off switch the tubes to the opposite channel and if the dead channel follows the tube switch you hopefully just need a new tube. My preamp has two tubes for the line stage and two for the phono stage, and they are mounted horizontally, see this https://www.usaudiomart.com/details/649252938-copland-cta-305/images/1150672/. I have lost a channel two times over the years. Both times were because somehow a perfectly good tube or the vertical board the socket is mounted into had lost connection with the preamp. The first time I lost a channel I removed and reseated the two line stage tubes in the same socket and all was well. The second time I lost a channel, with the system off I just gently nudged the tube a little and the channel came back. Not sure why this happens but only twice in many years of use. If that doesn’t work, while the lid is still off, as a poster mentioned above explore if by chance the RCA connecter in your preamp is damaged. From here, if you haven’t already, I guess I would switch speaker cables left to right to make sure I don’t have a bad solder joint on a speaker connecter and if that doesn’t help with my limited knowledge of electronics its off to the shop for repair. |
Here's why tubes can be a major PITA! Tonight, I figured one of my tube mono blocks was down...so I swapped in my ss Rowland stereo amp ( in place of the tube mono blocks) for a night of music and lo and behold...the same darn issue persists!! No sound out of the right channel! This is so very odd as my first thought, see my OP, was to do this test and the sound was fine before when the ss amp was in the chain. This would seemingly now mean one of two things..a) the preamp has a problem or b) the right speaker is blown. I swapped over speakers...put the left speaker on the right side and vice versa ( easy to do with stand mounts, luckily) Nope--the right channel is still silent. Hmmm. Seems to be a preamp issue ( which could still mean a tube has gone away, as I use a CAT tube preamp...) So, onwards we go... |
So tonight I swapped out the 12ax7 driver tube...and after a few minutes of idle power...a loud and nasty hum and buzz through my right speaker! ( the same channel that was acting up before!) I quickly powered down...and decided to change out all of the power tubes. ( I figured this might be a classic power tube failure). Upon replacement of all KT150's, I powered up again. This time, no loud hum and buzzz...no apparent issue at idle. I switched on the high voltage...and sure enough..same channel is still down!..:0( I'm pretty flummoxed at this point, so I think next is off to the dealer. |
@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-- |
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? |
@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( |
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. |
I had a very similar problem recently but in my case the left channel amp would kick out a very nasty hum to my speaker. I opened the amp up and everything looked fine. I ran another pair of rca cables from my surround sound system which is separate from my stereo system and had the same problem.I was going to take it out for repair but decided to take one more look and again everything looked fine. When I touched the connection to the rca input it moved away from the connector. A little soldering fixed the problem. |
@gdnrbob, Thanks, who knew when we got into this hobby that one had to learn to be a detective as well as everything else, LOL. @millercarbon The plug in question is a WBT locking RCA. I suspect that there is indeed a bad solder joint. The cables in question are Nordost Tyr's...which have been very reliable up to now. I am probably going to have to send it back to Nordost for servicing. |
Yes. Had a bad solder joint inside the RCA of one interconnect. Very hard to find as it worked fine for so many years, then gradually progressively acting up. Seemed from the beginning to be a connection issue, but exactly where? Intermittent faults are the worst. You get there but slowly. Eventually narrowed it down to inside the plug, and still wasn't sure (just seemed so unlikely!) until taking it apart the wire just pulled right off! Re-soldered, and no problems since. Yours sounded from the start like another contact problem. In your case parts expand as they heat up, eventually reaching a point where they lose contact. It could be like mine where its inside the IC, where the wires solder to the pins. Or it could be the RCA connection itself. Even a tiny amount of play could be enough for the IC to wiggle just enough for the signal pin, the part that sticks out, to lose contact with the clip, which is inside where you can't see it. Not saying its either one, only saying now its narrowed down to a smaller area you have to really zoom in on every little thing going on in that area. |
