New Millett Hybrid MiniMAX (what happened to this thread?) - Page 107

From Pete Millett in the original Millett Hybrid article in AudioXpress magazine: 

 Note that in the same article, Pete measure 0.5% output distortion with both the 12AE6 and 12FM6.

I am sure the answer to this is somewhere in this 107 page thread, and I apologize accordingly, but how doable is the minimax as a first-time DIY project? Is there something cheaper I should try first to get used to the build process?

My standard recommendation is that everyone should build a CMoy, first:

http://www.tangentsoft.net/audio/cmoy-tutorial/

 

There are quite a few who've built a MiniMAX as their first kit, but it's not been without some struggle in some cases.  I think the MiniMAX makes a great 2nd project, but probably not a 1st one.
 

Sorry for the delay in getting the pics up.  Been out of town.  

 

Here are the pics (sorry for the crappy quality, I'm no photographer).

 

 

Top:

 

 

 

I get sound out of the right channel.  Nothing out of the left channel.  

 

Thanks for all of the help so far jdkJake and Tom!

 

Wow. Seriously, at least you should clean your PCB before doing any debugging. I suspect there's a short somewhere in the PCB.

Welcome back drclaw.



I have to agree with lil'knight, if you do a quick clean of the board, it will be easier to see any error.



Right off the bat, I see quite a few cold solder joints, but, it is hard to tell with all of the flux in the way. Go to your local drug store and pick up some 91% rubbing alcohol. A big bottle is like $1USD. Also pick up the cheapest nylon toothbrush they have. I bought this serious large pack of them for like $2USD. They are terrible quality for teeth, but, are really handy around the house for various cleaning chores. Carefully clean and scrub the back of the board. There are some further details on the miniMAX (and other max) sites. Then take another picture and send it off.



Also, for the top of the board, if you can get a shot straight on and with more light, I think I would be much easier to see that all the various parts are installed correctly.

EDIT: I meant 91% and not 97%, sorry!
Edited by jdkJake - 7/31/10 at 1:27pm

Ha I knew that was going to be the first thing said!  I cleaned off as much as I could.  

 

Here are the pictures.  

 

 

Top side:

QB2L and QB3L are reversed.  Look at the silkscreen.  They are actually supposed to be upside down compared to the same ones on the right side.  You've installed them in the same orientation on both channels.

I de-soldered them, but when I got QB3L out, one of the leads fell off.. 

PM me with your address - I'll send you a couple more.

I've been searching the threads and I think I found part of the answer. However, since I'm a noob at this, I want to ask anyway.

 

Is the 12FK6 a better tube for the audiotechnica AD700 than the 12FM6?

 

Is there enough difference in the sound for me to try the 12FK6?

Trust me, you want as low gain as possible, so go for the 12FK6. And I would strongly recommend that you use 10 or 22R output resistors.

This is tubes ....!  There is always a reason to try a different tube.  Only you can tell if you like the difference ... but there will be a difference.
 

Yes, there can be a LOT of difference. 

 

Give them all a shot, Millett tubes are a bargain!! Especially compared to some other more exotic tubes. I suggest you have at least one set of each (12AE6, 12FM6 and 12FK6) to try out. Different construction makes for different sonics as well. Collecting them can become quite the habit.

 

Heck, rolling tubes is half the fun of a tube-based amp! Dig in and have some fun!

I have the 10R installed in my minimax.  I guess I'll order the 12FK6 and give it a try.