Finished Crack build, need help with low voltages [resolved]

[timindq]

I finished building my Crack yesterday with only minor issues during construction. After what was a fairly successful resistance check I went back and retouched a few solder joints, soldered some unsoldered wires and actually put in a missing wire. At that point the resistance check went fine.
When I turned it on to check voltages I ran into some real problems. There were some serious under voltage readings associated with the left channel. Also, the led connected to pin 3 on the 12AU7 wasn't glowing. I'll list the voltages which are incorrect. First listed is the connection point as labeled followed by the voltage reading.
5 - 10v
9 - 63v
A1 - 8v
A6 - 80v
B1 - 80v
B6 - 65v
The voltage on the hot side of the unlit LED is 1.2v while the voltage on the lit LED is 1.5v.
After looking everything over again and again I plugged in a source and a pair of headphones. The result was clean audio in the right channel and only static type noise in the left channel. The noise doesn't vary when the volume pot is turned.
Any advice is appreciated here. Thanks.

 

[Paul Birkeland]

What voltage do you have on T4?

 

[timindq]

My meter reads 5.6VAC and 0VDC.

 

[timindq]

Let me clarify, by T4 I'm assuming you meant the transformer's #4 which is 5.6VAC. If you meant #4 on the terminal strip up front, the measurement is 181VDC. In my original post the only readings listed are the readings which are out of tolerance.

 

[Paul Birkeland]

181V on T4 and 0V on T5 indicates either that the 22K resistor isn't well connected on one end, or you have a short to ground on the T5 end, maybe at the 9 pin socket.

-PB

 

[timindq]

Yes, it was shorted to ground. I could see no reason for the short so I removed the black lead from the transformer and the tube sockets are no longer shorted. The tab #4 on the transformer is shorted to ground with nothing attached to it. Please advise.

 

[timindq]

So sorry but I just got out my mag glass and checked the tab on the transformer. The shorted tab is #5. Tab #4 is also shorted of course as it has a black wire tied to the chassis as directed.
The transformer is wired correctly, it's just my missreading of the tab number earlier.

 

[timindq]

After further checking, I'm certain the windings in the transformer are shorted between pins 4 and 5. No idea how to proceed from here.

 

[Paul Birkeland]

Please leave the power transformer terminal connections as they were when you first built the kit.

The terminals I was referring to are terminals 4 and 5, which are on the front 5 lug terminal strip. 

-PB

 

[timindq]

I reattached the black wire to the transformer tab #5. Before doing this I took resistance measurements with the following results:
A1 to A6 read 44.2K ohms - I measured at these points to ensure I wasn't disturbing the resistor connections at the terminal strip as they look ok.
A9 to ground read open
B8 to ground read open
After reattaching the the wire at the transformer, A9 and B7 read short to ground.

 

[timindq]

I reattached the black wire to the transformer tab #5. Before doing this I took resistance measurements with the following results:
A1 to A6 read 44.2K ohms - I measured at these points to ensure I wasn't disturbing the resistor connections at the terminal strip as they look ok.
A9 to ground read open
B8 to ground read open
After reattaching the the wire at the transformer, A9 and B7 read short to ground.
Appreciate the help so far.

 

[Paul Birkeland]

Perhaps you could post some photos of your build?

 

[timindq]

Will do. Thanks.

 

[timindq]

Attached (hopefully) are the pics I took. There are some irregularities in the wire color because I used some Audioquest wire stripped out of a piece of excess cable. I used them in places where audio signal is passed as best I could figure. The pieces are 20 gauge solid copper.
Also, the black wire running from the transformer to the 6080 has been unwound from the red wire after I disconnected it. I will replace both wires after we sort this out.

I hope these pics tell you something. Thanks.

 

[Paul Birkeland]

Can you pull the 6080 but leave the 12AU7 in, then remeasure terminals 1, 2, 4, and 5. (Not power transformer terminals, terminal strip terminals)

 

[timindq]

Thanks for the reply.
Do you mean measure voltage or resistance? I want to check before applying power without the tube.

 

[Paul Birkeland]

Measure voltage with no 6080 installed.

-PB

 

[timindq]

Thanks,

Voltages are:
1 - 95 VDC
2 - 224 VDC
4 - 224 VDC
5 - 8 VDC

 

[Paul Birkeland]

OK, now repeat the test with both tubes pulled.

Do note that the power supply will take several minutes to drain down after you turn the amplifier off when run with no tubes.

-PB

 

[timindq]

With both tubes pulled

1 - 225 VDC
2 - 230 VDC
4 - 225 VDC
5 - 9 VDC

Thanks