Problem with one channel going out.....

Since it's always the same channel, think about the slip on connections to the phono cartridge. One at a time, slide the connections on and off.a few times to clean up the contact between the cartridge and the tone arm wire. You can put a little more squeeze on the connectors by putting a tiny squeeze on the conncctor when it is off the cartridge. TINY!. Look for a broken wire. Do this with the power to the phono preamp off. It is possible for the wire to break inside the insulation. Is there a noticable hum on the dead channel? That would indicate the cartridge connections are poor or the cables from the TT to the preamp are bad. The electronics are probably OK. Good Luck!

Ask the guy with a finicky SS amplifier whether tubes are more finicky than SS.

It sounds to me tube amplifiers are more finnicky than solid state.  Hope the sound difference is worth the bother.  Perhaps this is why they manufacture solid state equipment.  However, tube amplifiers do sound warmer.  I wonder what produces the most accurate sound.

A little late in the game for this suggestion, but always note if this problem is on cold start up or when the system is good and warm.  Is it really random is my question.  This of course is not a fix and the posts above will get you to a conclusion.  I have used the bottom up method several times to successfully troubleshoot my system.

Heat (or lack thereof) can do things!

Regards,

barts

You pure and simply have a connection problem somewhere... you said that you looked at the solder joints... that's no good... you can have a crack in the joint that is almost impossible to see and can only be solved by resoldering... You have a tube amp but you still have capacitors also which can cause the problem... The problem happens when you listen for a while which means that once the components heat up and expand causing the problem.... If it were a pot problem (volume knobs etc) it would occur right as you turn the system on and would stop once you wiggled the knobs around...You need to have a tech look at it. I think you said you have isolated it to the preamp... so take the preamp in.

A can of Deoxit (or your favourite contact cleaner) will probably be a good point to start.  Remove connections (including power), apply the contact cleaner and reconnect, working the contacts together in order to allow the cleaner to do its job.

Possible other causes *might* also include actual broken components (capacitors, transistors, diodes, and resistors) can all fail both open circuit and closed circuit.  PCB tracks can fail (eg. a capacitor that leaks electrolyte onto a PCB can cause corrosion and cause issues.

If you've already replaced all the thermionics, then the issue is probably elsewhere...

The fact that you say the signal is there, but a greatly reduced volume along with what you've already done makes me think of a possible component fault.

If you think it is the phono stage you have to substitute another phono stage to see if the problem stops. Intermittent problems are the bane of electronics. Before you return a unit you have to be loaded for bear or the manufacturer will just tell you the unit is working fine. 

Good luck!!

Tube sockets can always go bad, and for a wide variety of reasons and due to many different causes. But in this case I am trying to understand how dirt could get into the socket that is already hosting a tube. Also, I think the OP mentioned he had done some things that would have eliminated poor electrical contact of a tube pin as a cause of his problem.

I would start at my speakers and work back.  You don't need to replace anything.   Since it is in one channel, all you have to do is swap cables and see if it moves to the other channel.  Swap speaker cables.  If it moves it is either in the cables or the speaker.  If not, put them back and swap cables from preamp to amp.  If it moves, it is upstream of the amp.  If it doesn't move, it is the amp. Keep working back and you can find it. 

Jerry

The deoxitD5 is indeed a great product.  I have the kit and have used it a few times on all of my tube connections.  Thank you

Here’s one more option to explore before sending your preamp off to Manley Labs. No matter how fastidious you are regarding the cleaning of the top surface of your preamp; with an open architecture it’s possible that you may have several contaminated/dirty tube pin sockets. It may be worth the time to use some Caig Labs Deoxit D5 (judiciously) with a tube pin socket cleaning brush.

You’ve mentioned already swapping tube sets and this would rule out any tube pin socket contamination as a potential culprit causing the problem.

Thanks kingharold and sgordon1...yes I've tried different carts and wiggled every single connection including the four pins at the cartridge.  Through further messing around I think it has to be an internal issue with an electronic component in the PreAmp.  It is truly maddening, I get to thinking I am being scientific about it all and narrowing it down...then it turns out to be something else!  But all clues are pointing toward the preamp output

Try gently wiggling cable connections, one by one, the next time you lose sound.  An unsecured connection may be the issue!  This has worked for me.

In the past I had the same problem with my previous LP rig.  It finally turned out to be the cartridge, a well used Sumiko Blue Point #2, which was intermittently dropping a channel.

I'm going to swap out the preamp with an Icon Audio one that I have at work tomorrow. Unfortunately, this issue comes and goes and it's not happening now.  But that's my next step.  I'll keep listening to it for a while and see if it happens again.  If it doesn't, I'll get in touch with Manley and send in the pre-amp for diagnosis/service.

I replaced the Chinook with a step-up transformer by simply swapping out the two.  It's a Bellini MT502.  It's not powered, it just increases the signal coming from the MC cart

Ditto.  But I am too lazy to do what I should do on that score.  I spent more than a year trying to detect the source and fix an oscillation in one of my amplifiers.  At the start, I had no idea how long and arduous would be the process.  After 6 months, I could not really be sure what I did in month #1, except that all efforts were failures up to that point.  Finally, I did fix the problem in spite of sloppy record keeping.

This is why I document all troubleshooting on paper, easy to go in circles when you forget prior moves.

How do you replace the Chinook with a transformer?

Thanks for the replies so far guys. Lewn, I wish I had documented my experiments better, but I didn't.

Just now I swapped out the Chinook for a transformer, and the problem persists. So it's NOT the phono stage or TT

Also, despite what I said earlier, the problem persists with other inputs as well...namely the CD player is on input 2, same thing.

Since I did notice the signal fall off on the CD recorder meter earlier, the problem must be with the pre-amp, since that is the only component which is a constant on all of these experiments.  Maybe next step is to take that component out of the mix, I do have another preamp I can try.  Ugh, so frustrating.

Will update result

Connect the right channel from the Chinook to the left channel input on the preamp, left channel from the Chinook to the right channel input on the preamp.  

If the problem remains in the right channel, the problem lies downstream from the Chinook.

If it moves to the left channel, the problem is the Chinook, cartridge, or wiring.

Can you re-hash your own trouble-shooting experiments, and the results in the simplest terms, minus the digressions?  Like, "swapped phono cables; this made no difference".  It doesn't help to know why you changed tubes, for example.

The fact that you do hear either very faint music or some low level noise on the R channel suggests that the problem is in one of the circuits somewhere.  A bad cable will usually give an all or nothing type of problem, or very loud hum.

It sounds like the phono section. If you swap phono section cables does it move problem to left channel? You need to isolate exactly where the issue is. Maybe borrow or buy a cheap phono amp to try. I had a hum issue with my Linn LP12 and a new tonearm RCA cable solved a bad ground issue in the phono cable. Also this only happens with TT? all other inputs OK? Sounds like the phono section, but could also be a bad cable.