Voltages off on 1u and 7u RESOLVED!

hibuckhobby

New member
When I first turned the amp on, the led connected to A8 lit right up.  After about 30 sec, it went out.
Voltage on terminal 1 is 151vdc.  All other voltages as well as the resistances check out.  Next steps?
thanks,
Hibuck....
 
Could we see a photo of the 9 pin socket area? 

That LED should not light right up when you start the amp up.

(You didn't, by chance, add flux when you were building?)
 
Phone pics...not the greatest, but here they are.
 

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I  can assure you it's not.
If you open the picture and then scale down your screen,
you can see pin 9 all alone with nothing on it.  Pin 8 measures 0v.
Could the led be bad?
 
Not trying to dunk on you, but the pictures are so blurry that it's really hard to tell what's going on. It might be easier to post a slightly less zoomed-in version of the photo.
 
I'm not really sure what to say here... Despite being blurry, I see an empty pin 8 on your 9 pin socket in two of the three photos you posted.

If you connected the LED to pin 9 by mistake, that will illuminate the LED immediately when you turn the amp on, then the LED will burn up and no longer work.

These are the conditions you listed and are verified by the photos you've provided. 

The solution to this issue would be to either replace that LED and hook it up between the center lug and pin 8 of the 9 pin socket, or to remove that LED completely and use a short piece of wire between pin A3 and pin A8 to use that LED to also provide bias voltage to A8.

 

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Paul,
My sincere apologies.  I "did" have the led wired to pin 9. (mea culpa)
I find that my resistance readings are "not" all good.  I had my helper
read them and should not have done that.  Terminals 1,2,4,5 and 13
all read 1.3-1.35 megohms.  Once I track that down, then I will run a
wire from A3 to A8 and see what we have.  Suggestions on resistance
readings?
Bob
 
That you for your patience Paul.  Once the 12AU7 was properly biased, everything
fell into place.  A few pops on first startup, but now very quiet.
Hibuck...
 
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