Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › [SripBoard Design] Starving Student Millett Hybrid Vacum Tube Amp
New Posts  All Forums:Forum Nav:

[SripBoard Design] Starving Student Millett Hybrid Vacum Tube Amp - Page 14

post #196 of 269
Thread Starter 

 

Quote:
Originally Posted by nikongod View Post


When I am the ruler of the world you can be my head negotiator. 


I can be sure of one thing, I wont be responsible of the technology advancements committee

 

EDIT: on a more serious note, all resistors match both side of the circuit.


Edited by TestSubject - 12/27/11 at 9:29am
post #197 of 269

That's a bummer. Measured from the furthest points? Tube socket and stuff. 

 

Measure the plate resistors to the positive voltage rail (power off of course)

 

Have you tried switching tubes from one side to the other? Its possible you have a bad tube. 

 

After that, its all about checking voltages. 

post #198 of 269
Thread Starter 

Have not checked the furthest point on all of them (did all the grounded resistors), but the sockets all check up. Will remake some test first thing tomorrow morning.

 

 

Quote:
Measure the plate resistors to the positive voltage rail (power off of course)

 

I am sorry I am not sure I understand.

 

I have switched the tubes and both seems to work.

 

About Voltages, Digger945 suggested i sampled voltages between pin 4 and 5

 

 

Quote:
One Channel measure 19Volts between pin 4 and 5 while the other 27 Volts...

 

Thanks much to both of you for helping me out! Of to bed now.

 

post #199 of 269
Quote:
Originally Posted by TestSubject View Post

 

I am sorry I am not sure I understand.

 

 

Measure resistance from the positive voltage supply line (with the power off) to pins 1&6 on both tubes. 

 

measure resistance from the gate (input) of the mosfet to the positive voltage line and ground. 

 

Measure resistance to ground from pins 8&3 (should all be the same) and pins 7&2 (also all the same - 7&2 should vary as you spin the volume control)

 

Measure as much as you can from the tube pins. This is key. Measuring just the resistors does not tell you if you skipped a solder-joint, or accidentally shorted something.

post #200 of 269
Thread Starter 

Okay after one more day of going through the circuit, i found a missing jumper, Ho boy I was happy, but one channel still doesnt work.

 

a26c3313_3.7.jpeg

 

Quote:
pins 7&2 (also all the same - 7&2 should vary as you spin the volume control)

 

The non working channel shows a significantly smaller resistance. Exemple, 2.7k while the other is around 12.2. However they both read 1k when pot is at one of its extreme

 

EDIT: all measurement are done without the tubes plugged in.

 

Thanks again


Edited by TestSubject - 12/28/11 at 9:17am
post #201 of 269

 

Quote:
Originally Posted by TestSubject View Post

The non working channel shows a significantly smaller resistance. Exemple, 2.7k while the other is around 12.2. However they both read 1k when pot is at one of its extreme

 


Do the values change correctly as you spin the volume knob? 

Measure them with the volume knob at every quarter or third of its rotation. for a 50Kohm pot it should be something like 1Kohm (volume all the way down) 2Kohm@1/3up, 10Kohm@2/3up, 50Kohm@max volume. Those are very rough numbers, from my head. Your results could be 50% different, but they should go something like that.

 

If the dead channel goes up to 2.7Kohm and stops, where the live channel keeps going up past 12.2Kohm this is something I would investigate. It sounds like you accidentally shorted the grid of the tube to the cathode, but thats a wild guess. To confirm this guess measure the grid-to-cathode impedance with the volume knob at max volume. It should be ~50Kohm.


Edited by nikongod - 12/28/11 at 9:38am
post #202 of 269
Thread Starter 

Okay, the non working channel does indeed stop increasing at 2.8K

 

However the working one, at full volume, it displays 28K

 

What on earth is going on...

 

EDIT: i checked, they are in sync until 2.8K


Edited by TestSubject - 12/28/11 at 9:41am
post #203 of 269

Do you have 50Kohm (or so) resistors across the input RCA's, not shown on the stripboard? that would explain why the good channel only goes to 28Kohm. 

 

What does the resistance from grid to cathode look like with the volume knob all the way up?

post #204 of 269
Thread Starter 

 

Quote:
Do you have 50Kohm (or so) resistors across the input RCA's

Yes I do, sorry for the un-complete design

 

Between Pin 2 and 3, the working channel reads: 30K were the other reads: 1K

 

EDIT: as always, measured with no tubes in

 

EIA-9A.png


Edited by TestSubject - 12/28/11 at 10:22am
post #205 of 269

Same thing when you swap tubes? 

post #206 of 269
Thread Starter 

I am afraid so.

post #207 of 269

I'm totally sure you have a short somewhere. 

 

My guess is that the 1kohm resistor between the grid(input) of the tube and the pot shorts to the strip that goes to the cathode on the side closer to the pot. It may also be where the pot wires to the board on that same strip. Flip the board and check there. 

post #208 of 269
Thread Starter 

I am very sorry sir but I need to go now, the amp sound so sweet to BOTH of my hears I really have no time to say thank you.

 

 

Warning: Spoiler! (Click to show)

After taking the Amp apart 4 times, and resoldering many times, I may have shorted the input to the cathode.

 

post #209 of 269

Cool! Glad its working. 

post #210 of 269
Thread Starter 

Everything is in place, will be taking shots soon.

 

I have one Mosfet heating more then the other. I really hope the heatsinks are big enough, I mean they are hot! The datasheet say 175 Degrees but...

 

EDIT: After putting a droplet of water on the Mosfets, the water evaporate, they are running over 100 degrees...

 

REDIT: Note that both tubes are not the same model, might explain the difference?

 

Also buzzing and clic-ing in the background at about 2/3 of the Volume.


Edited by TestSubject - 12/28/11 at 4:30pm
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › [SripBoard Design] Starving Student Millett Hybrid Vacum Tube Amp