Crack not functioning - guidance requested

[DenverDude]

Hello - A few months ago I rolled a tube in my Crack w/ Speedball from the stock 6080 to a NOS Tung Sol 5998 tube. When I turned the unit on with the 5998, there was a buzz coming out of the left channel for the first 30 minutes or so and then would dissipate and not be present (and the sound was amazing) until I would turn off the unit and then turn it back on, when the buzz would again commence for 30 or so minutes and dissipate.

Doc suggested I resolder all the connections to my tubes and clean the tube elements, so I did that this weekend. I re-installed the 6080 on the unit and it worked fine all day yesterday. Today I reinstalled the Tung Sol 5998 to see if the problem was the tube or the soldering, and the buzz was present when I first turned the unit on. So I walked away for an hour or so to let the buzz dissipate, and now the unit does not work at all. When the unit is on, the tubes do not heat up and there is no sound. When I turn the unit on, I can hear a slight "click" in the headphones, but that's all.

Any assistance would be much appreciated ... thanks.

[oguinn]

Did you redo the resistance and voltage checks? It’s probably still a bad connection but those can tell  you where it’s happening.

[Paul Birkeland]

Perform the voltage checks and post them here. 

Do the tubes glow at least?

[DenverDude]

Thanks Paul and oguinn - The tubes are not glowing. I will perform the resistance and voltage checks tonight and post them. Thanks for your help

[DenverDude]

Here are all my checks:

Resistance Readings
1 - Wander
2 - Wander
3 - 0 ohms
4 - Wander
5 - Wander
6 - 2.481K ohms
7 - OF reading
8 - 0 ohms
9 - OF reading
10 - 2.481K ohms
12 - 0 ohms
13 - starting at 0 climbing slowly to ~280K ohms
14 - 0 ohms
20 - 0 ohms
22 - 0 ohms
B3 - OF reading
B6 - OF reading
RCA Ground - 0 ohms
RCA Center - 93K ohms

Voltage Readings
 1 - 5.9 V
 2 - 232.1 V
 3 - 0 V
 4 - 231.8 V
 5 - 230.1 V
 6 - 0 V
 7 - 1.7 V
 8 - 0 V
 9 - 1.6 V
 10 - 0 V
 11 - 0 V
 12 - 0 V
 13 - 231.3 V
 14 - 0 V
 15 - 236.5 V
 20 - 0 V
 21 - 241.1 V
 
 A1 - 229.6 V
 A2 - 0 V
 A4 - 0 V
 A5 - 0 V
 A6 - 7.6 V
 A7 - 0 V
 A9 - 0 V
 
 B1 - 7.2 V
 B2 - 232.4 V
 B3 - 1.7 V
 B4 - 230.8 V
 B5 - 232.2 V
 B6 - 1.6 V
 B7 - 0 V
 B8 - 0 V

[Paul Birkeland]

You need to focus on getting the tubes to glow.  If neither tube glows, then the wiring to B7/B8 from the power transformer is broken or poorly soldered.  There is absolutely not anything else you should focus on until you can get the tubes to glow; all other problems are completely meaningless until the tubes can conduct.

[DenverDude]

Hello Paul - I was finally able to get the tubes to glow and the Crack functioned fine for about 2 weeks until I started to get buzzing in the left channel, and tapping on the top of the unit would affect the buzzing.

So I went in and re-soldered every terminal and connection that wasn't part of a circuit board. Now when I plug in the unit the tubes will glow but I have zero voltage in any of the terminals.

At this point I feel that I'm over my head and I don't know how to fix this unit, so I was wondering if I could ship this to you and have your team repair it for a fee. Just let me know... thanks for your help

[Paul Birkeland]

Could you post some photos of your build?  It seems very obvious that you have some flaky solder joints in the amp.  When it's all said and done, a flat rate repair will cost you roughly $200 with all the associated shipping costs, and reflowing every joint in the amp takes about twenty minutes.

[DenverDude]

Hello Paul - I went back and resoldered additional terminals and connections.Both tubes are glowing, and here are my voltage checks:
1 - 183 V
2 - 188.3 V
3 - 1.1 mV
4 - 188 V
5 - 79.1V
6 - 3 mV
7 - 180.4 V
8 - 1.3 mV
9 - 111.9 V
10 - 1 mV
11 - 1 mV
12 - Negative lead
13 - 187.3 V
14 - 0.6 mV
15 206.6 V
20 - 0.3 mV
21 - 225 V

A1 - 79.9 V
A2 - 1.3 mV
A4 - 0.2 mV
A5 - 0 mV
A6 - 181.4 V
A7 - 1 mV
A9 - 0 mV

B1 - 181.4 V
B2 - 186.8 V
B3 - 180 V
B4 - 79.3 V
B5 - 186 V
B6 - 112 V
B7 - 0.4 mV
B8 - 0.2 mv

I have gone back and resoldered A3 and Terminal 1 two additional times and am still getting high voltage readings for those. Any guidance or advice would be appreciated

[Paul Birkeland]

If you've resoldered the LED terminals a bunch, you may have damaged an LED.  If you have 12V on A3 or A8, you have reheated an LED enough to destroy it.  If the other LED is still working (which it seems to be), you can install a short wire jumper between A3 and A8 to restore proper functionality.

[DenverDude]

Thanks for that advice, Paul.

I added a jump wire between A3 and A8 and now the unit is working. However, I get a steady low buzz from both channels with the CRC-6080 supplied with the Crack, and when I plug in a NOS Tung-Sol 5998 that I purchased, the buzz gets louder, especially in the left channel.

Also, the left channel seems to have a touch less gain than the right. Here are my voltage readings:
1 82.3
2 176.3
3 0
4 175.4
5 82.1
6 0
7 108.6
8 0
9 109.4
10 0
11 0
12 na
13 175.5
14 0
15 194.4
20 0
21 213.8

a1 81.4
a2 0
a4 0
a5 0
a6 82.0
a7 0
a9 0

b1 82.0
b2 174.6
b3 108.3
b4 81.3
b5 175.4
b6 108.7
b7 0
b8 0

Any ideas on what I need to address ... thanks again for your assistance.

[DenverDude]

Also at this point I have re-soldered every primary connection within the unit (with the exception of the speedball circuits) twice in the last few months. And the other tube in the unit is an ECC 82.

[DenverDude]

At this point I'd like to ship this to you and have you fix what is wrong with this circuit. I have done my level best but I'm not an expert at this and after hours soldering and testing, I am at the end of my ability and patience in trying to troubleshoot this. Just let me know where I need to submit payment and what I need to do to ship this to you. Thanks for your help ...  I really do appreciate it.

[Paul Birkeland]

I get a steady low buzz from both channels with the CRC-6080 supplied with the Crack,

Is this buzz at all dependent on the volume knob position?  If yes, is it there with the knob all the way down?  If the buzz is there regardless of the volume knob position, this tends to suggest a loose solder joint on a filter capacitor. 

There's still more debugging that can be done via the forum, and I would hate to have you spend all the money to send your amp to me for me to fix something like a simple soldering issue.

[DenverDude]

Thanks for your patience, Paul.

So when I first turn on the device, there is no hum. After the unit warms up, anywhere from 30 to 120 minutes after usage, then the hum develops, mostly in the left channel but it's evident in both. It also affects the gain of the left channel slightly (it's a skosh quieter than the right channel).

When the hum is present, it is there regardless of the position of the volume knob (zero or louder). Also, if I tap the table where the unit is positioned or I tap the unit itself, I hear it through the headphones. And when I lift up the left side of the unit, the hum dissipates.

Also, the hum sometimes goes away and returns randomly during longer listening sessions (3 hours or longer ... I sometimes listen to this all day when working).

I hope that helps...