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New Millett Hybrid MiniMAX (what happened to this thread?) - Page 119

post #1771 of 1944
Sweet.

That must have been some good beer!
post #1772 of 1944

Its new home, breaking in some 701s.

 

GetAttachment.aspx.jpg

 

People who know me don't believe me when I say I built it.


But then I explain the support network.

 

And they still don't believe me...  as I said,  They know me.

post #1773 of 1944
Quote:
Originally Posted by FishHead View Post

Its new home, breaking in some 701s.

 

GetAttachment.aspx.jpg

 

People who know me don't believe me when I say I built it.


But then I explain the support network.

 

And they still don't believe me...  as I said,  They know me.


And we're glad we could help you look so professional in your handiwork.

It looks right at home on that desktop. 

post #1774 of 1944

Looks great!

 

I assume it sounds as good as it looks?

post #1775 of 1944

Hey guys, I'm back. I'm done fiddling with my amp. I simply have no idea what to do and where to look. I need a professional. 

 

Is there anyone I can send it to to figure out whats wrong with it? Or could my local electronics shop fix it? 

post #1776 of 1944
Giving up on her already, huh?

Well, sorry to hear that. I was hoping we could walk you though it and get it up and running. However, I understand, you have to be willing to do it, or what is the point.

Not sure who could fix it for you. I am in the middle of another project (actually two), so, I really cannot take it on right now. Maybe in a few weeks. I would love for you to hear what that great little amp is capable of.
post #1777 of 1944

BobSaysHi, where in Texas are you located?

post #1778 of 1944


 

 

Quote:
Originally Posted by jdkJake View Post

Giving up on her already, huh?

Well, sorry to hear that. I was hoping we could walk you though it and get it up and running. However, I understand, you have to be willing to do it, or what is the point.

Not sure who could fix it for you. I am in the middle of another project (actually two), so, I really cannot take it on right now. Maybe in a few weeks. I would love for you to hear what that great little amp is capable of.

 

Quote:
Originally Posted by ShinyFalcon View Post

BobSaysHi, where in Texas are you located?



Not to worry - we've found someone who's going to help BobSaysHi.

post #1779 of 1944



 

Quote:
Originally Posted by BobSaysHi View Post

Hey guys, I'm back. I'm done fiddling with my amp. I simply have no idea what to do and where to look. I need a professional. 

 

Is there anyone I can send it to to figure out whats wrong with it? Or could my local electronics shop fix it? 


Just a preliminary look, BobSaysHi, but you've got several resistors mixed up in the primary tube circuit and CCS sections.  That may be more than enough to cause the high-current drain.  I'll keep studying it and let you know the specifics when I find them.

 

EDIT: It appears that the resistors are mixed up everywhere.  Just as a gentle reminder for future reference for everyone, item #3 in the MiniMAX notes included with each kit states the following: "3. ... Despite what package the resistors are in, they may all be different.  Make certain you either measure them or you understand the exponential notation of the rating."

 

To make this even clearer, I'm editing the MiniMAX Notes to read as follows:

3. Please, please, please – install the V-D resistors (the little brown ones) so that the rating (the exponential numbers) is visible from the top of the board.  Despite what package the resistors are in, they may all be different values.  You must select the correct value resistor and match it up with the correct designation on the PCB.  Make certain you either measure them or you understand the exponential notation of the rating.  A 1K resistor will show “1001F.”  A 100R resistor will show “1000F.”  1M is “1004.”  The notation works by 100 multiplied by 10 to the power of the last number.  Smaller resistances such as 10R are shown as “10R2” (actually 10.2 ohms) or something similar.

 

 This is going to take me awhile, BobSaysHi ... 
 


Edited by tomb - 9/24/10 at 10:23am
post #1780 of 1944


 

Quote:
Originally Posted by tomb View Post



 


Just a preliminary look, BobSaysHi, but you've got several resistors mixed up in the primary tube circuit and CCS sections.  That may be more than enough to cause the high-current drain.  I'll keep studying it and let you know the specifics when I find them.

 

EDIT: It appears that the resistors are mixed up everywhere.  Just as a gentle reminder for future reference for everyone, item #3 in the MiniMAX notes included with each kit states the following: "3. ... Despite what package the resistors are in, they may all be different.  Make certain you either measure them or you understand the exponential notation of the rating."

 

To make this even clearer, I'm editing the MiniMAX Notes to read as follows:

3. Please, please, please – install the V-D resistors (the little brown ones) so that the rating (the exponential numbers) is visible from the top of the board.  Despite what package the resistors are in, they may all be different values.  You must select the correct value resistor and match it up with the correct designation on the PCB.  Make certain you either measure them or you understand the exponential notation of the rating.  A 1K resistor will show “1001F.”  A 100R resistor will show “1000F.”  1M is “1004.”  The notation works by 100 multiplied by 10 to the power of the last number.  Smaller resistances such as 10R are shown as “10R2” (actually 10.2 ohms) or something similar.

 

 This is going to take me awhile, BobSaysHi ... 
 

 

Oh, well that would explain why it wasn't working.

 

That is definitely what I did wrong. I didn't think to check the values when they were in the packages.

 

I didn't make it easy for you either, and I apologize for that.
 

post #1781 of 1944
Quote:
Originally Posted by BobSaysHi View Post


 

 

Oh, well that would explain why it wasn't working.

 

That is definitely what I did wrong. I didn't think to check the values when they were in the packages.

 

I didn't make it easy for you either, and I apologize for that.
 


's all right - just give me time.

 

P.S. Funny thing is ... I could've sworn we asked you to confirm the resistor values.
 

post #1782 of 1944

I finished building my miniMAX last night, and have taken some measurements - for some reason the tube bias won't budge from around 23V  no matter how much I turn the trimms.

The power supply is biased to 27V, both DB are sitting at around 90mV. I'm using the 12FK6 tubes atm, I have some 12FM6s aswell which I haven't tried yet.

 

Cheers!
 

post #1783 of 1944
Quote:
Originally Posted by rayk View Post

I finished building my miniMAX last night, and have taken some measurements - for some reason the tube bias won't budge from around 23V  no matter how much I turn the trimms.

The power supply is biased to 27V, both DB are sitting at around 90mV. I'm using the 12FK6 tubes atm, I have some 12FM6s aswell which I haven't tried yet.

 

Cheers!
 


Some questions -

1. Are the tubes lit?  Do they get warm?

2. How many turns on the RA1 trimmers have you tried?  Note that those trimmers are picked for 3 types of tubes with widely varying gains.  That means for one tube type, you may have bias adjustment in the first 3 or 4 turns.  For a different tube type, it might be 3 or 4 turns somewhere in the middle of the 25-turn(!) trimmers.  For the third tube type (out of 12AE6, 12FK6, 12FM6), it might be the last 3 or 5 turns out 25.

 

Granted, that's an exagerration to illustrate the example, but hopefully you get the point - don't give up on turning the trimmers.  it's somewhat difficult, but another thing you can check is the trimmers themselves.  Put a DMM probe on the un-traced pin of a trimmer on the bottom of the PCB, then place the other probe on one of the two pins that are on the trace.  Measure the resistance (all of this with the power off!), turn the trimmer 5 turns or more, then measure again.  If you see an obvious change in resistance, then they're OK.  Note that you may need to try turning in both directions when making this measurement if the trimmer happens to be at the end of its travel when you start.

 

Try those things and then let us know what's going on.

post #1784 of 1944

Yep the tubes get warm and light up. I think I'm about 25 turns or so, so I will try checking the trimmers tonight. Haven't tested the amp for sound yet either  smily_headphones1.gif - I think it was on for a total of 30minutes, so not sure if the tubes are still breaking in (first time dealing with a tube amp) smily_headphones1.gif

 

Cheers Tom for quick reply!


 

 

 

post #1785 of 1944
Quote:
Originally Posted by rayk View Post

Yep the tubes get warm and light up. I think I'm about 25 turns or so, so I will try checking the trimmers tonight. Haven't tested the amp for sound yet either  smily_headphones1.gif - I think it was on for a total of 30minutes, so not sure if the tubes are still breaking in (first time dealing with a tube amp) smily_headphones1.gif

 

Cheers Tom for quick reply!


 

 

 


Well, if the bias is at 23V, you're probably not going to get any sound.  Breaking in tubes may change the bias by a few volts, but not that much.  The tube part of the amplifier circuit is very simple, though, so my guess is that there's nothing bad wrong - especially if you already have the DB's biased to 90mV.  My guess is that you haven't turned the trimmers enough or in the right direction.
 

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