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I have read here and on the headphone sites of the hum problem and of various solutions with this amp. My unit has/had a hum straight out of the box. After about 20 hours the unit is silent as long as I use the 6SN7 that came from the factory. The other 6SN7s that I have (Electro Harmonix, Electro Harmonix gold pin, and Tung Sol) all still produce a hum, mostly in the left channel. Since these tubes are not NOS then I am assuming that it is not a tube problem. Am not equipped to start moding the unit (have read about the fritz mod), so should I expect this problem to go away in time and/or should I be running the noisy tubes in the unit to aid this process ? Thanks for any advice available.
Either you got bad tubes, or there's still gas in 'em.
Bear in mind, most tubes you buy online for cheap are of poor quality and/or were stored in poor conditions.
Other than that, there's a remote chance you're having a ground loop. May I ask whether you're using the amp in the U.S or abroad?