C11 - Left side does not play a sound ?

ofery

Active Member
Hello,

Just got a C11 from eBay, but there is one problem - the left side does not play a sound, only the right side.
Tried to switch the main cables (L to R and R to L), the sound then moved to left - means left side still does not play a sound.
I tried to turn the left red input level control, but still left side still does not play a sound.
Tried other input device, the same ...
Tried to switch from Stereo to Mono (L+R), the same ...
This C11 worked OK before it's been shipped.
Any idea what can be the problem ?

Regards /Ofer
 
Before I shipped it back or took it to a tech I'd invest in a can of De-Oxit and Faderlube and clean every switch and pot. Then if it still doesn't have a left channel it's time for a tech.
 
I have uninstalled & installed all the 6 tubes, the left side has returned to normal ...
But ... after ~30 minutes the left side started to show sound distortion.
Buy the way, this C11 has been professionally restored by Audio Classics at NY.
It seems like a tubes problem, maybe they been damaged at shipping.
Any idea ?
 
Well.... after playing around, it seems to be a grounding issue. The distortion occurs when I touch the body of the C11.

Any idea what can cause it ?
 
Bad tube pin contacts or a bad tube. Swap tubes individually left for right channel and see if problem stays the same or moves.

Dirty switch

Cold solder joint somewhere in left channel path.

The first you can do yourself, sometimes just unplugging and reinstalling a tube will clean the sockets enough to clarify the issue.

If you have Deoxit and Faderlube this should always be your first option.

Finding cold solder joints drives any tech nuts.
 
I have uninstalled & installed all the 6 tubes, the left side has returned to normal ...
But ... after ~30 minutes the left side started to show sound distortion.
Buy the way, this C11 has been professionally restored by Audio Classics at NY.
It seems like a tubes problem, maybe they been damaged at shipping.
Any idea ?

I saw that one. Looked like a good price. Hope you get it working.
 
Problem probably solved - bad tube !
Replaced it & it works great.
Many thanks for your help.
 
Hi all,

Well ... it seems that the problem has not been solved yet after all.
After a ~hour of play, I'm getting a noise from left speaker.
Tried to replace all tubes with my spare tubes, but it did not solve the problem.
After a long test, I found that the noise came from the left tube (when you face the rear).
The "noise" occurs when I'm gently tapping on the left tube with a pen.
Other tubes, do not sound a noise when I tap on them.
So I assume it's probably a bad socket or capacitor/resistor & not a faulty tube, since I replaced the tubes.

Any idea what can cause it ?
What the left tube does in C11 ?

Regards /Ofer
 
you need to get it to a good local tech and make sure that it's checked out properly. There are any number of things that could be wrong. BTW, not bashing audio classics in any way but I have an mc225 that was "rebuilt" by them and they made a number of deviations from the stock circuit, some good, some kind of questionable. They left the bumble bee caps in place in the voltage doubler circuit, as well as leaving some of the original electrolytics in the bias supply circuit and elsewhere. They also left all of the original glass diodes in place. I've since replaced all of those items.
 
sounds like a microphonic tube, I'd swap that one tube out with your others until you find one that isn't microphonic. If you could, please take a shot of the underside of the preamp, with the bottom plate removed of course. I'm betting you have some bad caps and out of spec resistors.
 
btw, never ever use deoxit on a tube socket. I'm sure there are plenty here who will reinforce that deoxit plus tube socket is a bad idea.
 
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