New Crack build voltages off [Solved]

OldManNiko · 1832

0 Members and 1 Guest are viewing this topic.

Offline OldManNiko

  • Newbie
  • *
    • Posts: 7
on: July 03, 2015, 07:34:35 AM
All my resistances checked within tolerance.  Bolstered by that confidence, I continuity checked the circuits to make sure my joints weren't dead then gave it some power.  I can see both tubes light up, both sides of each, However only one LED is lighting [A3] (my first indication of an error). I went ahead and took measurements for voltage.  Here's the numbers I got.  Any ideas on where I should start? 

1   -> 147    (75-90) *
2   -> 163.3 (170)
3   -> 0        (0)
4   -> 163.3 (170)
5   -> 77 ( 75-90 )

6   -> 0 ( 0 )
7   -> 146 ( 100 ) *
8   -> 0 ( 0 )
9   -> 101.7 ( 100 )
10  ->0 ( 0 )

11  ->0 ( 0 )
12  ->0 ( 0 )
13  ->163.2 ( 170 )
14  ->0 ( 0 )
15  ->186 ( 185 )
16 N/A
17 N/A
18 N/A
19 N/A
20  ->0 ( 0 )
21  ->208.5 ( 206 )

a1  ->77 ( 90 )*
a2  ->0 ( 0 )
a3  N/A
a4  ->0 ( 0 )
a5  ->0  ( 0 )
a6  ->147.7 ( 90 ) *
a7  ->0 ( 0 )
a8 N/A
a9  ->0 ( 0 )
 
b1 ->147 ( 90 ) *
b2 ->164 ( 170 )
b3 ->146 ( 100 ) *
b4 ->77 ( 90 ) *
b5 ->164 ( 170 )
b6 ->102 ( 100 )
b7 ->0 ( 0 )
b8 ->0 ( 0 )

* denotes voltages that are concerning me.
« Last Edit: July 03, 2015, 05:09:10 PM by OldManNiko »



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19757
Reply #1 on: July 03, 2015, 07:43:00 AM
Can you see two glowing dots on the top of the 12UA7?

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OldManNiko

  • Newbie
  • *
    • Posts: 7
Reply #2 on: July 03, 2015, 08:08:10 AM
Both tubes are lighting properly.  Here's some pics of the tubes lit as well as the LEDs on the A tube base.



Offline Strikkflypilot

  • Sr. Member
  • ****
    • Posts: 459
  • Shellac fiddler
Reply #3 on: July 03, 2015, 08:33:07 AM
It is not possible to verify the polarity of the LEDs from You pictures but the A8 led looks situated very close to a blob of solder on the center pin. Scorched?

Home system:
Sources: Ibasso DX90, Google Chromecast Audio optical out
DAC: Schiit Gumby
Amp: Bottlehead Mainline
http://bottlehead.com/smf/index.php?topic=7463.0
Phones: HD800S

Office:
Sources: Iphone/ Ipod
DAC: Dragonfly Red+Jtrbug
Amp: Crack/Speedball heavily modded
Phones: HD580,HD600 grilles


Offline OldManNiko

  • Newbie
  • *
    • Posts: 7
Reply #4 on: July 03, 2015, 08:37:37 AM
Yep it's a scorched LED.  I unsoldered it, and was not able to get it to light independently.  I doubt the local Fry's will have a replacement, so I'll await a new LED from the fine folks at Bottlehead.  Does this explain the voltage irregularities elsewhere in the circuit? I have no idea.  But I know I cannot proceed any further without the LED as it seems to provide much more than some light, bias voltage if I am correct.



Offline Strikkflypilot

  • Sr. Member
  • ****
    • Posts: 459
  • Shellac fiddler
Reply #5 on: July 03, 2015, 10:51:29 AM
AFAIK these LEDs are there to make sure 1.5vDC is drawn for bias voltage for each side of the 12AU7(cathode biased). If You have a working LED, I believe it is ok to short A3 to A8. Correct me if I am wrong, Paul.
« Last Edit: July 03, 2015, 10:53:15 AM by Strikkflypilot »

Home system:
Sources: Ibasso DX90, Google Chromecast Audio optical out
DAC: Schiit Gumby
Amp: Bottlehead Mainline
http://bottlehead.com/smf/index.php?topic=7463.0
Phones: HD800S

Office:
Sources: Iphone/ Ipod
DAC: Dragonfly Red+Jtrbug
Amp: Crack/Speedball heavily modded
Phones: HD580,HD600 grilles


Offline OldManNiko

  • Newbie
  • *
    • Posts: 7
Reply #6 on: July 03, 2015, 05:11:30 PM
AFAIK these LEDs are there to make sure 1.5vDC is drawn for bias voltage for each side of the 12AU7(cathode biased). If You have a working LED, I believe it is ok to short A3 to A8. Correct me if I am wrong, Paul.
Thanks for the help.  Jumpering did the trick.  Now to warm it all up.  No noise at all that I can hear.  I'll do another voltage check tomorrow to make sure heating the unit hasn't cause some value changes.  Again thanks for the help in getting this going!