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The Christiansen "DG" 300B Amplifier Build Thread - Page 33

post #481 of 630
Thread Starter 
Quote:
Originally Posted by tomchr View Post
 

 

There's hum in the headphones even with all the valves unplugged? That makes no sense at all.

 

~Tom

Very light. A background hum.  Faint, certainly compared to with them in.

post #482 of 630
Quote:
Originally Posted by sceleratus View Post
 

What about TU1 and TU3, pull those as well?

 No. The whole point is to let the small-signal tube amplify whatever hum may be on its input so you can measure it. 

 

~Tom

post #483 of 630
Thread Starter 

WIth the OPT shunts in,

With the DMM in Max/Min/Ave mode probes to left and right chan P2 will start at 60mV and drop quickly to 20mV continuing to  drop from 15mV but slowly.  Pulling the probe resets the sequence.   I presume this is a cap activity.

post #484 of 630
Thread Starter 
Quote:
Originally Posted by tomchr View Post
 

 No. The whole point is to let the small-signal tube amplify whatever hum may be on its input so you can measure it. 

 

~Tom

ok

post #485 of 630
Thread Starter 

WIth TU1 and TU3 in the Grid voltage on TU2 and TU4 rose from -232V (spec) to -76V

 

EDIT:

 

Reading the startup procedure this is the correct voltage for TU2/TU4 Grids when TU1 / TU3 is insertyed.

 

There is still a faint hum.


Edited by sceleratus - 9/4/13 at 5:44pm
post #486 of 630
Thread Starter 

 

 

With valves TU1 and TU3 in, I clipped to the J8 ground on the Driver Board and probed Pin 2 of the output jacks.

The image of the higher amplitude wave is the Right Channel.  Multiple exposures were taken to catch the wave phase shift.   If these are of any use at all...

 

 

 

 

 

 

post #487 of 630

Suggestion: Use the line trigger on the o'scope. If the hum really is 60 Hz (or harmonics), the scope should show a clear image.

 

~Tom

post #488 of 630
Thread Starter 

I ride the short bus.  My o'scope has these triggers:

 

Edge, Pulse Width, Video, Slope, Alternate, Pattern and Duration Trigger 

 

 

I'll see what I can find on YouTube


Edited by sceleratus - 9/5/13 at 8:40am
post #489 of 630
Thread Starter 

Probably a good idea....

I get the exact same wave form when the amp is OFF

post #490 of 630
Quote:
Originally Posted by sceleratus View Post
 

Very light. A background hum.  Faint, certainly compared to with them in.

 

Magnetic coupling. 

post #491 of 630
Thread Starter 

Couldn't get a grasp on triggers after several YouTube tutorials....

Magnetic coupling must be really strong since I moved the OPT's an additional 1" to 1.5" further from the face of the power trans.

Hard to imagine this popped up now after testing in death trap mode and running production for over a month.   I also looked at transformer positioning of the Electra-Fidelity Silver 45.  Eyeballing it my distances are equivalent to greater.

 

 

 

 

 

 

Reached Max-Q of my abilities.  I'm in "box up" mode now.

post #492 of 630
Quote:
Originally Posted by nikongod View Post
 

 

Magnetic coupling. 

 

It might be, or it might be environmental though I think flourescent lights should show up as 120Hz.

 

Suggestion, move to a different room.  Also, add extra wire (2 feet) to the output transformers and move that away in an aggressive manner.  Move the output XLR jacks with the transformer.  Solder the wires, and scotch electrical tape (rated to 600V) to wrap.  I'm not sure about generics.

 

Quote:
Originally Posted by tomchr View Post
 

Suggestion: Use the line trigger on the o'scope. If the hum really is 60 Hz (or harmonics), the scope should show a clear image.

 

~Tom

 

I would like to see a single cycle as well, but this is probably good enough.

 

Quote:
Originally Posted by sceleratus View Post
 

I ride the short bus.  My o'scope has these triggers:

 

Edge, Pulse Width, Video, Slope, Alternate, Pattern and Duration Trigger 

 

 

I'll see what I can find on YouTube

 

Just hit all of them, to experiment.  Start with Duration, trigger on high (not sure if there is a voltage level to set, but if so, set to something like 1mV), and capture about 60ms of data.

 

The noise pictures you are posting is the same as what was on the output.  Was this with the input connected to the input XLR?  Can you disconnect it and ground the inputs to the driver board?

 

Also, can you probe the input XLR jack?  I think you may have done this already, I forget.

post #493 of 630
Thread Starter 
Quote:

 

Just hit all of them, to experiment.  Start with Duration, trigger on high (not sure if there is a voltage level to set, but if so, set to something like 1mV), and capture about 60ms of data.

 

The noise pictures you are posting is the same as what was on the output.  Was this with the input connected to the input XLR?  Can you disconnect it and ground the inputs to the driver board?

 

Also, can you probe the input XLR jack?  I think you may have done this already, I forget.

Tried many different scope trigger configuration.  I didn't know what I was looking at.

 

I probed the driver board with all the inputs removed.

 

Doesn't matter now.  It's in a box

 

Thanks to everyone for the suggestions and encouragement.  Wish I could have figured it out on my own.

post #494 of 630

Damn... I'm curious to hear what Jack finds out.

 

~Tom

post #495 of 630
Thread Starter 
Quote:
Originally Posted by tomchr View Post
 

Damn... I'm curious to hear what Jack finds out.

 

~Tom

 

you have no idea........ actually you do.

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