Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: OldManNiko on July 03, 2015, 07:34:35 AM
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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.
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Can you see two glowing dots on the top of the 12UA7?
-PB
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Both tubes are lighting properly. Here's some pics of the tubes lit as well as the LEDs on the A tube base.
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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?
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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.
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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.
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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!