Post by troublereport on Oct 12, 2016 8:59:44 GMT -6
WARNING!! Here’s a note for all you out there looking to replace the 6386 tubes in your variable mu limiter. JJ seems to be the only manufacturer that can supply these tubes new. I’m here to tell you, they are NOT the same as the original 6386. NOT.
I ordered four tubes (yes, they cost $120 each) for a Fairchild 670 for one of my high profile clients. I installed the tubes I received from Tube Depot in one channel. They behaved very differently from the original tubes in the other channel. You’ll say “Well, they’re new. Duh”. And they did perform well with respect to distortion and noise.
The problem is, the transconductance profile is vastly different from the original. The first indication is that it draws a lot more current at idle than the original – so much so that with all four new JJs in one channel, it was impossible for me to “zero” the unit in question. I finally chose to use two original 6386s and two new JJs in each channel. With this arrangement I was able to zero it. Even so, as I called for gain reduction I found that the meter reading had no relationship to the actual amount of gain reduction. With five dB of GR, the meter indicated 10dB. My client decided to go with the discrepancy and get on with life. But what happens when the other original 6386s wink out and need to be replaced?
JJ includes a “helpful” little sheet that provides the test results for the particular tube you have bought. It indicated that across the four tubes I had in my possession, there was a fairly large difference, from a quiescent current draw of 14mA (not too far off the original) to 20mA. I contacted Tube Depot with my concerns. I wanted Tube Depot, or JJ, to hand select a set of tubes that conformed more to the 14mA end of the spectrum. I discovered quickly that Tube Depot is just there to sell you the tube – after that, best of luck. They did provide me with an email address for the folks at JJ in the Slovak Republic, and I began a dialog with them, once again asking for a set of hand selected tubes. Maybe there was a snag in translation, but no matter how I worded the request in multiple email, the answer I received was that “JJ would not change the way it manufactured its tubes” The final exchange wrapped up with the technician berating me for my lack of knowledge of tubes and vowing not to respond any further to my emails. He has held true to his word. I promised him I would bring this all to the attention of the pro audio community – here we go.
Conclusion: Buying JJ 6386s is just as much a roll of the dice as any other solution.
I ordered four tubes (yes, they cost $120 each) for a Fairchild 670 for one of my high profile clients. I installed the tubes I received from Tube Depot in one channel. They behaved very differently from the original tubes in the other channel. You’ll say “Well, they’re new. Duh”. And they did perform well with respect to distortion and noise.
The problem is, the transconductance profile is vastly different from the original. The first indication is that it draws a lot more current at idle than the original – so much so that with all four new JJs in one channel, it was impossible for me to “zero” the unit in question. I finally chose to use two original 6386s and two new JJs in each channel. With this arrangement I was able to zero it. Even so, as I called for gain reduction I found that the meter reading had no relationship to the actual amount of gain reduction. With five dB of GR, the meter indicated 10dB. My client decided to go with the discrepancy and get on with life. But what happens when the other original 6386s wink out and need to be replaced?
JJ includes a “helpful” little sheet that provides the test results for the particular tube you have bought. It indicated that across the four tubes I had in my possession, there was a fairly large difference, from a quiescent current draw of 14mA (not too far off the original) to 20mA. I contacted Tube Depot with my concerns. I wanted Tube Depot, or JJ, to hand select a set of tubes that conformed more to the 14mA end of the spectrum. I discovered quickly that Tube Depot is just there to sell you the tube – after that, best of luck. They did provide me with an email address for the folks at JJ in the Slovak Republic, and I began a dialog with them, once again asking for a set of hand selected tubes. Maybe there was a snag in translation, but no matter how I worded the request in multiple email, the answer I received was that “JJ would not change the way it manufactured its tubes” The final exchange wrapped up with the technician berating me for my lack of knowledge of tubes and vowing not to respond any further to my emails. He has held true to his word. I promised him I would bring this all to the attention of the pro audio community – here we go.
Conclusion: Buying JJ 6386s is just as much a roll of the dice as any other solution.
