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New Millett Hybrid MiniMAX (what happened to this thread?) - Page 118

post #1756 of 1944

Finished but not Finished.

 

v+ to Grnd:   26.5 vdc

 

All screws turned clockwise until clicking.

Ta2R to grnd:    20+ VDC  Final value not seen as power button mashed.  

Ta2L to grnd:    20+ VDC  Final value not seen as power button mashed.

Tb2R to grnd:    20+ VDC    "       "                                              "'

Tb2L to grnd:    20 + VDC   "      "                                               "

 

Pretty Leds light nicely.  No smoke.  No solder bridges seen.  No hot electronic smells (I mash the buttons when 20 VDC arrives).

 

IMG_1884.JPGIMG_1887.JPG

 

 

Thanks in advance.

post #1757 of 1944
Quote:
Originally Posted by FishHead View Post

Finished but not Finished.

 

v+ to Grnd:   26.5 vdc

 

All screws turned clockwise until clicking.

Ta2R to grnd:    20+ VDC  Final value not seen as power button mashed.  

Ta2L to grnd:    20+ VDC  Final value not seen as power button mashed.

Tb2R to grnd:    20+ VDC    "       "                                              "'

Tb2L to grnd:    20 + VDC   "      "                                               "

 

Pretty Leds light nicely.  No smoke.  No solder bridges seen.  No hot electronic smells (I mash the buttons when 20 VDC arrives).

 

IMG_1884.JPGIMG_1887.JPG

 

 

Thanks in advance.


Well, TA2R to GND and TA2L to GND set the tube bias.  Turning the RA5 trimmers all the way clockwise is not going to accomplish anything but increase your frustration when you try to bias the tubes.

 

As for the Diamond Buffer bias, the measurement is TB2R to TA2R and TB2L to TA2L, not to GROUND.   All you're doing is repeating the measurement of the tube bias by measuring those test points to ground.  Please refer to this page to review what we're trying to bias:

http://www.diyforums.org/MiniMAX/MiniMAXsetup.php

 

In the case of the buffer, all the test points provide is a measurement across the the RB10 and RB11 resistors.  Either one can be measured to set the bias.  All four resistors are 2.2 ohms.  So, if you measure in mV (you cannot measure milliAmps in this instance), you only need to divide by 2.2 to get the mA of bias through the circuit.  Again, though, you are not measuring to ground when biasing the buffer - only the voltage across the resistors connecting the complementary output transistors in the push-pull arrangement.

 

So, please  and carefully - set your probes in TA2L and TB2L, turn the power on, note the mV reading, and turn the power off.  If it's less than about 40mV, then that's OK.  Set the probes in TA2R and TB2R and turn the power back on.  If it's less than about 40mV again, then turn the power off.  You're OK and need to turn your attention to biasing the tubes.  Refer to this page again:

http://www.diyforums.org/MiniMAX/MiniMAXsetup.php

 

 

P.S. Nice stone table, btw.  Also, your work looks very good.  I'm sure once we verify the correct points to measure, you'll be able to get it up and running in no time.
 


Edited by tomb - 9/12/10 at 5:14pm
post #1758 of 1944

 

v+ to Grnd:   26.5 vdc

 

All screws turned clockwise until clicking.

Ta2R to grnd:    20+ VDC  Final value not seen as power button mashed.  

Ta2L to grnd:    20+ VDC  Final value not seen as power button mashed.

Tb2R to grnd:    20+ VDC    "       "                                              "'

Tb2L to grnd:    20 + VDC   "      "    

 

Ta2R to Tb2R:  36.4 mv

Ta2L to Tb2L:  35.7 mv  

 

I am glad you are smarter than I look.  

 

We now return you to your regular programming.

If this was a real emergency ....

I would have gone and gotten a homebrew!  

post #1759 of 1944
Quote:
Originally Posted by FishHead View Post

 

v+ to Grnd:   26.5 vdc

 

All screws turned clockwise until clicking.

Ta2R to grnd:    20+ VDC  Final value not seen as power button mashed.  

Ta2L to grnd:    20+ VDC  Final value not seen as power button mashed.

Tb2R to grnd:    20+ VDC    "       "                                              "'

Tb2L to grnd:    20 + VDC   "      "    

 

Ta2R to Tb2R:  36.4 mv

Ta2L to Tb2L:  35.7 mv  

 

I am glad you are smarter than I look.  

 

We now return you to your regular programming.

If this was a real emergency ....

I would have gone and gotten a homebrew!  


Yep - you look fine on those DB bias points.  You should be free and clear to bias the tubes, etc.  Let us know how it turns out!
 

post #1760 of 1944

Currently 

 

Ha, I said Currently:

 

27 v+ to Ground

23.48 ta2R to Ground

23.49 ta2L to Ground

110.1 mv         ta2R to tB2R

110.1 mv         ta2L to tB2L

 

No amount of turning RA1l or RA1r is moving the readings.  Temping though it is to attach a drill to the little blue BOURNS tool (a minute or so should prove something),  I would like to try something else first.  

 

I am open for suggestions:  Oh, and I have had the amp on all day to stabilize temps.  No problems noted.  Amp is fairly cool.

post #1761 of 1944
Have you tried both directions? At least 20 or 30 turns?
post #1762 of 1944

Another question - are the tubes lit?  Do you see an orange glow in the middle rod of the tubes?  Depending on tube construction, it may only appear as a single point in the top of the rod or at the bottom where the pins are connected to the various internal tube pieces.

 

Jake is also correct - if you confirm the questions above, then perhaps you haven't moved the trimmers enough.  If you screwed them all the way down clockwise, note that I mentioned earlier that this would only increase your frustration in trying to find the happy medium of the tube adjustment.  You may have to literally turn 20 turns or more in the counter-clockwise direction before you see a response in lowering the voltage.

 

Check these things out and let us know ...

post #1763 of 1944

Yep,  First clockwise until I though I heard a click then I just kept a going while watching the meter.  Nothing changed.

 

Then I decided to see if anything would change at all. So I turned it the other direction say thirty times.  Nothing changed.

 

That is when I had the impulse to hook up the electric drill and see what it would do.  Fortunately I fought that urge down.

 

Since both L and R are doing the same thing I am guessing I did something in the Power supply area.  I am fighting the urge to poke around until cooler more experienced heads point me in the right direction.  

post #1764 of 1944

Hi Tomb,

 

The tubes are beautiful.  All blue with a little orange tip glowing.  They are hot to the touch but not burning hot.  The two middle heat sinks are hot to the touch but not burning hot.  The two outside heat sinks are cool and the power supply heat sink is cooler than the tubes but hotter than the outside heat sink.

post #1765 of 1944

Well I chucked up the bit and started toward the amp......

 

Must have scared something loose because I turned it on and no voltage to the Right side.... Must lay of the beer after work.... Check the left side. 23.5 V.  

 

Well if the right side changed I better check the Mv.    345 mv! dang WAY too much beer after work.  Turn it off.  Mash the power button and re adjust the mv.  110.  Nice

 

Turn it off yada yada yada.  Adjust what moves.  yada yada.... look!  Now tube voltage goes down if I turn it counter clock wise.  Well what do you know.

 

Dial everything in.  Come in and type this note and hope it is all good when I go back to check if it was just not a beer hallucination.  (I love spelling checkers)

 

If you see a picture of a completed box next... all is well.

post #1766 of 1944

What are you using as your ground reference? What point on the board?

 

EDIT: Hopefully, Never mind!


Edited by jdkJake - 9/13/10 at 5:49pm
post #1767 of 1944

No offense, but I thought counter-clockwise on the tube trimmers was the only way to go ... you cranked them down all the way they'd go clockwise to start.  Based on your description, either you haven't turned them enough counter-clockwise, or you destroyed the RA1 trimmers.  That's because everything you've related so far sounds like you've built everything correctly.  So, we're dealing with a little anxiety and lack of patience perhaps?  Just kidding!   Let us know what you find when you exercise those tube bias trimmers some more ...  Meanwhile, I'm grabbing another Sierra Nevada Torpedo from the frig ... I'll check for your posts in another short while and hopefully you'll find music at the end of this trial ...


Edited by tomb - 9/13/10 at 6:46pm
post #1768 of 1944

Other consideration...... make sure your volume control is at zero to try and bias the tubes. I found that funky things happen to the bias if you accidentally have the volume up.

post #1769 of 1944

  Done and in Spec!  Thanks for the advice!

 

110 mv all around

13.5 v tubes

27 v power.

Now to see how it sounds.

IMG_1893.JPG

post #1770 of 1944

Another MiniMAX lives!!

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