Crack way over voltage

[RankStranger]

Hi all,

I purchased a used crack with SB upgrade that the vendor swore was working fine. Unfortunately, he didn’t secure it properly for shipping and the top plate came loose, causing some damage. Apologies in advance for the long post. I figure some context may help.

The speedball big board came loose from one of its spacers and was hanging askew. There seemed to be no other damage so I reattached it and plugged it in but I only got the faintest crackly signal at full volume through my headphones. I unplugged it and upon inspection I noticed that two of the wires connecting the SB big board to the Crack (G and OB) had broken, either unnoticed with the other damage or while I was reattaching the board. I reattached these according to the instructions and, assuming (perhaps stupidly) that I had fixed the issue, tested again with the same result.

Per the speedball instructions, I did a voltage test on the large board and got the following (I’m in Australia on 240V, if it matters)

OA - 178V
OB - 219V
G - 0.2V
B+ - 243V

Then I got depressed and left on the bench for two weeks :/

When I came out of my funk, I rechecked the whole circuit and found a bad connection on the octal socket (B3), which I fixed. Optimistically, I voltage tested the main circuit and got the following

1 - 72V
2 - 240V
3 - 0V
4 - 243V
5 - 70V

6 - 0V
7 - 230V
8 - 0V
9 - 162V
10 - 0V

Then I retested the SB big board and got 178V on OA and 233V on OB.

I’ve rechecked it step-by-step twice and I can’t find any other errors or bad joints. I have checked through the forum and I can’t find any other posts with such high voltages.

On top of all this I got a short from something on the SB big board while I was double-checking my voltage measurements. I would be very grateful for any guidance on what I’ve likely fried or just missed. Happy to post photos but I’m not sure of what.

Thanks,

Simon

[Tom-s]

Is the 6080 glowing? Does the resistance check on the speedball boards pass?
Then; I'd start with double checking all connections on the Speedball large board (focus on the ground path first).
Second, double check all connections to and from the 6080 tube and their path to the Speedball board.

[RankStranger]

Yes, both tubes are glowing.

I think I missed the resistance check, I was concentrating on the crack circuit. I’ll try that and come back.

Thanks for your guidance

[Paul Birkeland]

Why didn't you send it back?

Which power transformer does this have?  How is it wired?  Pictures of the build?

[Doc B.]

Why didn't you send it back?

You're starting to sound like me as you get older.

This points to a fundamental issue that is often overlooked by assembled Bottlehead kit buyers. The stuff is only as good as the skill level of the person who built it allows. And so you need to decide if it is better to troubleshoot your own mistakes in a build or someone else's (including their lack of experience packing) before you buy used.

[Paul Birkeland]

I think I missed the resistance check

You will not get 3K at 7 and 9 with the Speedball boards installed, so don't fixate on that if/when you notice it.

[larcenasb]

You're starting to sound like me as you get older.

Lol xD

[RankStranger]

Why didn't you send it back?

Excellent question. Perhaps I’ll later regret not doing so but the fact is I bought it for a pretty good price with some good spare tubes and I was between projects so I thought it would be fun and not too difficult to get it working. Honestly, even if I have to break it right down to parts and rebuild it, I’d still be happy with the price I paid and the extra tubes I got with it.

I’ll try to post some pics tonight after I do the resistance check.

Thanks for your replies

[RankStranger]

Both OB and OA came back as "overlimit" on my DMM

On the main board all the resistance checks were good except that the ones that were supposed to be 2.9k (ignoring 7 & 9) came back overlimit too, even when I had the DMM set to kOhms. I don’t know enough to know if that’s a problem

Here are some photos. Not sure if I’ve taken them of the right things but I can retake some if I haven’t. I feel compelled to apologise for the messy soldering, even though it’s not mine

[RankStranger]

I'll try the photos at a more manageable size

[Deluk]

The pot wiring looks to be reversed compared to my standard crack but I don't think that affects voltages.

[Paul Birkeland]

In the beginning of the Crack build manual, there are instructions for how to attach and solder wires and components to terminals in the Crack.  These instructions were not followed.

Every joint in that amp needs the solder sucked off of it, the wires need to be crimped to their attachment points, then they need to be resoldered.

Without doing this, reliability problems are likely to continue popping up. 

[RankStranger]

Thanks, Paul

Am I better off tearing it down to parts and starting again? It’s not ideal but I really don’t mind doing it. The only thing missing (I think) would be the resistors that get removed when the SB is installed. Is there anything else? If the original owner can’t send them to me, can I just substitute temporarily with the same value resistor of any type?

Thanks, Simon

[Paul Joppa]

Parts list in the manual calls out resistor type and watts rating.

[RankStranger]

At my local supplier I can only get  3.3k ohm 5W wire wound resistors in place of the 3k ohm 10W ones and 22k ohm 1W carbon film resistors in place of the 22.1k ohm .5W ones that were removed to fit the speedball upgrade.

Will these work, at least temporarily? My plan is to remove the speedball mod and get the crack running without it by fixing the soldering job

Thanks