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New Millett Hybrid Maxed Amp - Page 426

post #6376 of 6600

Thanks, Jake.

I'm really torn about whether or not to keep the tube protectors. Anyone have any thoughts?

post #6377 of 6600

How long did it take for your tubes to burn in, guys? I'm going insane over here trying to bias. I keep thinking I've got it, then it changes on me. I think I've got about 15 hrs on them. Do they need more?

 

-Edit-

Nevermind, I found the answer to my questions.


Edited by scootsit - 3/2/12 at 11:16am
post #6378 of 6600

This left biasing is killing me. I leave it for hours, get it set to ~13.5. If I turn off the power and power it back on (I had to move it into a different room) after about 10 mins, the right tube is already settled to ~13.55, and within the hour, settles to 13.5. The left tube on the other hand will sometimes fall all the way to 12.5, or jump to 14.3. I think my left trimpot is bad, I just ordered a new one from mouser, so hopefully that takes care of it!

post #6379 of 6600
Quote:
Originally Posted by scootsit View Post

This left biasing is killing me. I leave it for hours, get it set to ~13.5. If I turn off the power and power it back on (I had to move it into a different room) after about 10 mins, the right tube is already settled to ~13.55, and within the hour, settles to 13.5. The left tube on the other hand will sometimes fall all the way to 12.5, or jump to 14.3. I think my left trimpot is bad, I just ordered a new one from mouser, so hopefully that takes care of it!


It could very well be a bad tube.  Try swapping them and see if the problem follows the tube.
 

 

post #6380 of 6600

Will do. I just placed an order with you last night. I might need to order a tube from you, did you ship it yet?

post #6381 of 6600

Nope - see your e-mail.wink.gif

post #6382 of 6600

I have a question. I was just doing some listening on my Millet Mosfet. I have been really enjoying it (even with one bad tube). Anyway, I was considering grounding my pot to the ground point next to it on the board and was evaluating if it was necessary (my case is already grounded through the center stand-off). I realized that when the volume is all the way up, there is a tiny bit of scratching in the left channel whenever I turn the knob. It sounds like a dirty pot, but this is a brand new RK27, which is sealed, so I doubt that. This is only audible at levels far above anything I would ever listen at and is very faint, so I'm not too concerned. But, I am curious as to why it would only be in one channel. I read that it could be the microphonics of the tubes, particularly since it was in the channel with the bad tube, I changed the tube and it remained. I wanted to switch to lower gain tubes, so I changed both tubes and now it has gone away. This is weird. I do notice a slight hum when I touch the pot so I need to ground it, but I cannot figure out the scratch I heard with the 12AE6As.


Edited by scootsit - 3/12/12 at 11:41am
post #6383 of 6600
Quote:
Originally Posted by scootsit View Post

I have a question. I was just doing some listening on my Millet Mosfet. I have been really enjoying it (even with one bad tube). Anyway, I was considering grounding my pot to the ground point next to it on the board and was evaluating if it was necessary (my case is already grounded through the center stand-off). I realized that when the volume is all the way up, there is a tiny bit of scratching in the left channel whenever I turn the knob. It sounds like a dirty pot, but this is a brand new RK27, which is sealed, so I doubt that. This is only audible at levels far above anything I would ever listen at and is very faint, so I'm not too concerned. But, I am curious as to why it would only be in one channel. I read that it could be the microphonics of the tubes, particularly since it was in the channel with the bad tube, I changed the tube and it remained. I wanted to switch to lower gain tubes, so I changed both tubes and now it has gone away. This is weird. I do notice a slight hum when I touch the pot so I need to ground it, but I cannot figure out the scratch I heard with the 12AE6As.

I have heard the scratchiness from time to time - but only when quickly moving the volume knob with certain tubes and capacitors (Black Gates).  As you say, it's not the pot.  There is some sort of phenomenon with the tubes that cause the scratchiness under certain scenarios.  Just an FYI, but running the volume knob to maximum with 12AE6's is like going through a black hole.  It's not normal, nor was it ever intended under regular circumstances.  I have seen the signal wave "flip" so that one channel is reversed from the other at high volume settings with 12AE6 tubes.  I suspect the gain outstrips the voltage available in the buffer at max volume without a load - weird things start to happen.  With a load connected (headphones), you will reach driver-blowing volumes much, much lower on the dial before you ever get to where the weird things happen. wink.gif
 

 

post #6384 of 6600

Oh, I was not concerned about it for listening purposes, just a weird phenomenon that I cannot explain. Thanks for the recommendation of the FK6s...they're like butta. No going back, and the dampeners seem to really make a difference. ANYWAY, I'll stop hijacking this thread with my non-sequiters and issues. Thanks a TON!

post #6385 of 6600

DC from your source can also make the pot sound scratchy.

post #6386 of 6600
Quote:
Originally Posted by Beefy View Post

DC from your source can also make the pot sound scratchy.


Good thought, Beefy!  That would explain why it seems to be heard so seldom and seemingly only with high gain tubes.  Perhaps just a trickle of offset from a source could be enough to induce some scratchiness when racking the volume knob.
 

 


Edited by tomb - 3/12/12 at 7:37pm
post #6387 of 6600

Wow, do I feel like an idiot.

I just searched through this whole thread and found that no matter what, tube bias may vary (once burned-in) by about 1/4V-1/2V. So, I've been driving myself NUTS, trying to get between 13.50 and 13.55V for nothing!

 

I also was convinced that the Mosfet voltage was varying whenever I adjusted the tubes, and the tube bias varying whenever I adjusted the Mosfets. It only very recently occurred to me that if I removed the top every time to adjust either, that the subsequent cooling would cause all voltages to increase (to some extent) every time, which is exactly what happens. Oy. A few more hours to let everything settle in, and I may FINALLY be done with biasing!!!

post #6388 of 6600

Yep.  Tubes are often like mules.  They're hard to get going in a certain direction. Once they do, it may be difficult to pull them back.  As you've found, it's effort wasted trying to get the bias precise.

post #6389 of 6600

Go easy guys, you're dealing with a techno-nullity.

 

Question: what is the output current of the MiniMax with the diamond buffer set-up? (I appreciate it will vary with tubes.) I'm asking because, with FK6s, I find this amp a very, very good match with AKG K701s & I'd like to recommend it to people who ask for numbers. I'm asking here because I can't seem to find the figures on the DIY site.

post #6390 of 6600
Quote:
Originally Posted by bruce108 View Post

Go easy guys, you're dealing with a techno-nullity.

 

Question: what is the output current of the MiniMax with the diamond buffer set-up? (I appreciate it will vary with tubes.) I'm asking because, with FK6s, I find this amp a very, very good match with AKG K701s & I'd like to recommend it to people who ask for numbers. I'm asking here because I can't seem to find the figures on the DIY site.

This is not as straightforward a question as it may seem.  The best way to put it is that the recommended setup will Class A bias the output transistors to 50 milliamps a piece.  So, that means at least that much current is available at the output before the transistors would go into a switching mode.  They'll supply much more than that if they enter a switching mode, but the sound quality may suffer.  That still means much higher transient currents may be available for music peaks (like bass thumps).  Beyond that, it's whatever the heat sinks and the walwart will put out before shutting down - or blowing the fuse.

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