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Old 13th June 2010, 06:16 PM   #1
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Default Ideas on weak left channel with static?

Got my completed TubelabSE checked out and into my audio room. Listened to some music and noticed my left channel outputting less than the right, and there is a little static creeping in there as well. Both channels have a slight buzz, owed to the Hammond 270HX transformer I suspect. I switched my output tubes and the static/weakness stayed with the left channel, so ruled out output tubes. I checked my voltage at the speaker posts while playing a 315Hz test tone, and got .28 volts on the problem left channel and about .48 on the right channel. Any ideas on what might cause this? Thanks,
Matt
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Old 13th June 2010, 07:19 PM   #2
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You are attacking this problem in the right way. Presuming that the right channel is operating correctly, work through from input to output checking DC conditions without any test tone, and looking for a point where the left channel diverges from the right...

If you have a 'scope you can look at your injected test tone, which will also help you localize the fault.

Exercise extreme care while fault-finding any tube amp, keeping one hand in your pocket is often recommended as a safety measure.

w
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Old 13th June 2010, 07:21 PM   #3
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Try swapping the input tubes? Also measure the voltage at the plates and across the cathode resistors of the input tubes.
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Old 13th June 2010, 07:24 PM   #4
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If that unit (I'm not familiar with it) has input switches, such as tape monitor, clean those. Very common cause of such problems.
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Old 13th June 2010, 08:28 PM   #5
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Thanks you guys!
Switched input tubes, and the problems followed the input tube, so switching them made my right channel affected. This is a bad input tube then! Thanks so much for the help. Now, to find a 5842 that isn't $60, that'll be the next chore.

Have a great rest of your Sunday,
Cheers,
Matt
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