Voltage problem [resolved]

[tfoust]

Finished the initial Crack build but voltage readings are 23 volts on terminals 5, 9 and 10.  What do you think caused this?  Bad capacitor?

[Paul Birkeland]

Please post some build photos.  In roughly 25 years of doing this, I have never seen a capacitor bad from the factory, but I have put plenty of them in backwards or on the wrong terminals and caused a lot of problems.

[tfoust]

Will take some pix this evening.

[tfoust]

I reflowed some solder joints and now terminals 5 and 9 read 23 volts.  Terminal 10 reads 0 volts.  Will post pix tomorrow.

[tfoust]

The led attached to pin 3 does not light.

[Paul Birkeland]

It would help to see build pics.

[tfoust]

Pictures taken last night

[tfoust]

Three more

[Paul Birkeland]

Can you post just a general top down photo as well as all the voltages on terminals 1-10?

-PB

[tfoust]

The voltage values read as follows

T1     85v
T2   199V
T3      0V
T4   199v
T5     24v
T6       0v
T7   118v
T8       0v
T9     23v
T10     0v

[Paul Birkeland]

If you run the amp with no 6080 but with the 12AU7 installed, does the voltage at terminal 5 increase?

The black wire running to the center post of the 12AU7 socket has a bit of extra jacketing stripped off, and if that bare wire rubbed against pin A1, that could create the exact symptoms you're encountering.

[tfoust]

Are both LEDs supposed to light at the same time?  The one closest to the edge of the chassis does not light when power is applied.  I didn't know if that changed when signal passed through the system.

[Paul Birkeland]

Don't worry about the LEDs lighting up or not lighting up.  The 24V that you have at T5 tells me that it's unlikely that the LED will light up.

We find that a lot of builders will focus very hard on the LEDs themselves and resolder them till they break when there's a different problem at work.  You most likely have two pieces of metal touching in your build that shouldn't, and that's pulling down terminal 5. 

The first test would be to pull the 6080 out of the amp and run it with just the 12AU7, then report the voltages on terminals 1-5 under those conditions.

If you have no changes from that test, then you would run the amp with no tubes at all and report the voltages on terminals 1-5 under those conditions.

[tfoust]

With the 6080 removed
T1 = 89v, T2 = 234v, T4 = 234v, T5 = 89v

[Paul Birkeland]

Though it is relatively rare with the testing procedures we do, it seems most likely that you have a 6080 that isn't quite working properly.  You can contact replacementparts(at)bottlehead(dot)com and request a replacement 6080.  Be sure to post a link to this thread and let them know that we worked on this together.

-PB

(PS - both LEDs would now be glowing too  )