New Crack + Speedball Troubleshooting

[hardisondan]

I completed my Crack + Speedball in one go (bypassing the installation of the resistors that I saw needed to be taken out later).

I went through the resistance checks and got some bad/inconsistent results. I was losing faith in the very cheap multimeter I bought, and in hindsight, maybe the batteries were a bit flat.

To cut a long story short, I plugged in and turned on the amp. The 6AS7 tube put on a bit of a multicolour light show. Purple, green, orange. Moving up and down the filaments. I thought maybe that's just what they do when they're warming up, but after a while I decided it wasn't looking right so I turned it off. I'm not sure if I've blown anything.

So I put fresh batteries in the voltmeter and went back and did more testing. These are the resistance measurements as best as I can tell.

1  0
2  0
3  couldn't reach (speedball boards in the way)
4  *
5  0
6  2.48
7  widely fluctuating
8  0
9  0
10  2.23k
12  0
14  0
20  0
22  0 (after jumping around)
B3  0
B6  0
RCAs ground 0, centre 100k


Should the resistance checks give the same results with Speedball installed? Resistors are removed in the installation, so I thought maybe not?

How do people turn the chassis upside down and work on it with the tubes in place?? I rested the wooden box on a couple of phone books with the tube down between them.

I have looked at my solder joints and I can't tell if any are obviously bad. Any advice on how I should proceed?

I am thinking (with heavy heart) I will remove the Speedball and restore it back to standard Crack, test and then re-add Speedball.

Dan

[Doc B.]

First and last sentence tells the story. Best to build it stock first, get it running right, and then add the speedball. Don't plug it in until you get it sorted out to the point that your resistance readings are all correct. If they aren't reading right after you remove the speedball and return it to the basic setup with the resistors you left out, post your readings here and we will help you sort it.

[hardisondan]

Thanks Doc. I knew I shouldn't do it!

[hardisondan]

Last night I restored it back to stock Crack and all the resistance tests passed! Tonight I will do the voltage tests.

Since I am in Australia, with 240v AC, what values should I get in the voltage tests?

Dan

[fullheadofnothing]

A 240V transformer connected to 240V will create the same voltages as a 120V transformer connected to 120V.

[hardisondan]

Thanks Joshua. I thought that might be the case.
Cheers

[hardisondan]

Here are my voltage test results. I don't know what to make of it. All the ones that are meant to be zero seem to be, but most others are out by a lot.

1 114V
2 225V
3 0
4 223V
5 113V
6 10mv
7 29V
8 0
9 9.2V
10 0
11 0
12 0
13 220V
14 0
15 228
20 0
21 237
A1 107V
A2 0
A4 0
A5 0
A6 111V
A7 0
A9 0
B1 113V
B2 223
B3 21V
B4 105V
B5 223V
B6 9.6V
B7 0 - 50mV
B8 0 - 30mV

B6 seems to be way way off.
B7 & B8 seem to fluctuate a lot.

Does anything here stand out as the most important thing to check?

Also, is the 6AS7 tube meant to glow purple? See attached.

Any advice greatly appreciated.

Dan

[Paul Birkeland]

B3 and B6 are way off.  Did you try the amp with the 6080 included with the kit?

Is the octal socket mounted properly? 

Does the 6080 glow?

Can you post some build shots?

The 12AU7 is mostly working, and things will fall into line when the issues around the octal socket are resolved.

-PB

[hardisondan]

Hi Paul,

I used the two tubes provided. The small tube has 5963 printed on it. I can't read any of the other markings.

The small tube does glow. At least it has two glowing filaments. Not sure how much it should glow. Its not as impressive as the big tube. See attached.

I've attached some photos. How should I test that the socket is mounted correctly?

Cheers
Dan

[hardisondan]

More build photos.

[Paul Birkeland]

I would do a bit of tidying before continuing.

The 22.1K resistors between 1/2 and 4/5 should be snugged up against the terminal strip as shown in the manual.  If they aren't, you've provided some slack for them to bend and touch other parts, potentially shorting out the high voltage supply.

The same thing goes for the 3.0K 10W resistors.  Take all that slack out on the octal socket end.  Feel free to use 7U and 9U if that makes it easier.  If the ends that are long are allowed to touch terminals 6 or 10, you will cook the 2.49K resistors on the headphone jack, and after they cook you will have 100V on your headphone jack (very bad).

As far as the amp itself goes, the big tube should glow visibly and obviously.  The red/black twisted pair from power transformer terminals 4 and 5 that goes to B7/B8 heats the tube.  Give those joints some additional heat to reflow the solder, then see if that helps. 

-PB

[hardisondan]

Thanks Paul,

I had trouble with those 22.1K resistors because I put them in, then changed my mind and snipped them out as I was trying to do the Crack+Speedball in one go. Then when I went to put them back in I had very little lead on one end of each. I might have to buy some new ones.
And with the 3.0K 10W resistors, I found there wasn't enough room between the terminal strips to get them in. Maybe my terminal strips were bent over a bit when I put the rising post things in for the Speedball. I will persevere and take your advice.
So are you saying the big tube might not be glowing enough? What about the small one? Does that look ok?

Thanks for your feedback.
Dan

[hardisondan]

Paul,
I have tidied up the loose ends of those resistors as much as I could. The 22.1K resistors are not perfect, but they are not touching anything and I don't think they will.
You must have had a premonition about the 2.49K resistors on the headphone jack, because one of them is in fact cooked. I don't think anything got shorted between 6 or 10 as you described, but you've obviously been doing this a lot longer than me!
So now I will need to replace that resistor, and I think I'll get some more 22.1k resistors while I'm at it.
Thanks
Dan