Crack Not Working After ~3 Years

[seanohue]

Hi, I have a Crack that I built in 2015 that no longer works anymore. It had been sitting, unused for around a year and when I went to turn it on again, no sound came out. I already reflowed all of the joints again and measured resistances and voltages. Resistances were all OK but I was measuring 0V instead of 100V on terminals 7, 9, B3, B4 and B6. I've already tried swapping the 6080 out in case that was an issue. It was glowing blue/purple about 2 years ago but still worked (I have video that shows this but can't do external links). Any suggestions on what could be wrong?

Resistances:
1 - 100k - Inf.
2 - 100K - Inf.
3 - 0.3
4 - Inf.
5 - Inf.
6 - 2.483K
7 - 2.938K
8 - 0.4
9 - 2.977k
10 - 2.486k
12 - 0.2
13 - Climbs to ~270k
14 - 0.8
20 - 0.5
22 - 0.6

B3 - 2.939k
B6 - 2.977k

Ground Lug - 0.3
Center Pins - 93.8k / 87.4k

Voltages
1 - 93.5V
2 - 217V
3 - 0V
4 - 218V
5 - 91.2V
6 - 0V
7 - 0V <-
8 - 0V
9 - 0V <-
10 - 0V
11 - 0V
12 - 0V
13 - 217V
14 - 0V
15 - 219V
20 - 0V
21 - 224V

A1 - 92.2V
A2 - 0V
A4 - 0V
A5 - 0V
A6 - 94V
A7 - 0V
A9 - 0V

B1 - 93V
B2 - 216.4V
B3 - 0V <-
B4 - 0V <-
B5 - 216.2V
B6 - 0V <-
B7 - 0V
B8 - 0V

 

[Paul Birkeland]

When you get 0V at those terminals, it makes me wonder if the 6080 is glowing.  (Is the base key broken off by chance?)

 

[seanohue]

When you get 0V at those terminals, it makes me wonder if the 6080 is glowing.  (Is the base key broken off by chance?)

The 6080 does glow, but only the two connections to the plates at the bottom of the tube.

 

[Paul Birkeland]

Well, the 6080 is not conducting.  Is the shiny getter on the 6080 tube still shiny, or turning white?

I would suspect a solder joint is not behaving correctly.  The junction of the black wires on the headphone jack seems to be one of the more common connections that causes problems.

-PB

 

[seanohue]

Well, the 6080 is not conducting.  Is the shiny getter on the 6080 tube still shiny, or turning white?

I would suspect a solder joint is not behaving correctly.  The junction of the black wires on the headphone jack seems to be one of the more common connections that causes problems.

-PB

Could you be slightly more specific about what the shiny getter is?  Though, I don't suspect it's the tubes because I did just try another NOS 6080 and had the same results.

I've already gone through and resoldered all of the joints on the amp again and the headphone jack looks fine (as far as I can tell).

 

[Paul Joppa]

Somewhere on the surface of the glass, there is a spot of shiny metal - postage stamp size, more or less - that looks like the glass is mirrored. It's a very reactive metal, which will absorb any gas inside the tube, and will turn white when it does so if there is more than a trace of gas - i.e. even a very tiny leak. It "gets" the gas out of the vacuum, so it's called a getter.

One of the ways that an old tube might misbehave, when first put in service after long disuse, is the gradual leakage of traces of gas from the internal components. A few tens of hours at operating temperature will restore the vacuum by heat-activating the getter. But of there's a lot of gas, and the getter is white, it can't be fixed.

 

[Paul Birkeland]

Can you post some photos of your Crack?  We might be able to spot the problem.

-PB

 

[seanohue]

Ok, see attached.

 

[Doc B]

Are the 6080s pins clean? One possible scenario is oxidation buildup on the tube pins and/or the socket contacts over that year that the amp sat unused.

 

[fullheadofnothing]

The untrimmed lead coming out of 19L looks like it is shorting to the other UF4007s. Even if it isn't it is a hazard that should be fixed.

 

[Paul Birkeland]

I'd also recommend reheating the solder joints on 3U and 3L.