2. amps-preamps
  3. 1301704400

Conrad Johnson Classic noisy channel.

I have owned this from new and upgraded it to se.Before and after the mod,the left channel tube rush becomes noisy after 3 months use.I am a moderate user,approx 3-4 hours use per day and do not leave the pre on when not in use.I have used 3 sets of mullard m8080/cv4058 tubes with the same result.Swapping tubes from left to right,noise swaps to right channel.Have had pre checked and all tube voltages are within spec.Are there any other classic users with this problem.Dave.
dre

Showing 2 responses by mlsstl

mlsstl
1,435 posts
 
I had a CJ PV10 preamp that developed noise after a number of years of use. It turned out to be a bad capacitor in the power supply.

It your case it sounds tube related, but it is possible that a circuit voltage is off and may be stressing tubes faster than normal. If that is the case, only a trip to a qualified shop is going to be able to find and fix the problem.
mlsstl
1,435 posts
 
An aside: odd how hard it is to pin down a minor issue in a new product.
I don't think small signal tube failure at 3 or 4 months is a "minor" issue. Doing some math based on the info given, the tubes in the one channel are going bad after 400 or 500 hours. The normal expectation for such tubes would easily be 10,000 hours and generally much more. His preamp tubes aren't even lasting a quarter of the expected life for a power output tube.

However, I suspect that in the hands of a good tech with proper equipment, the underlying problem would quickly reveal itself. However, it is not a problem easily fixed by the unaided consumer.
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