Left Channel Spontaneously Dead [resolved]

[Voxelr]

Hello! I have had an issue with my Crack + Speedball and would super appreciate some help, if possible. My knowledge and experience with DIY electronics is beginner, at best, so bear with me.

I had bought the Crack + Speedball kits a few years back, and was able to put them together and enjoy a working kit for a couple years, but I turned the amp on one day to discover that the left channel had gone out. Up until then, everything worked perfectly fine.

I've finally gotten around to pulling it back out and trying to get it to work again and could use some pointers.

A couple things to note:

• The two LED's on the Speedball's big board towards the bottom right (picture attached) no longer light up.
• I tried running the voltage tests in the docs. Of note, terminals 9 and OA both seemed to measure ~1.4V. Everything else appeared to fall within expected values

Otherwise, I have been unable to observe anything else wrong. Any help here would be appreciated! Thank you

[Paul Birkeland]

You will need to perform the voltage check provided in the build manual in order for us to provide any information on what might be going on.

[Voxelr]

Thanks for getting back with me, Paul. I ran the checks before and only noticed issues with the two aforementioned terminals. Let me double check my results and post the full readings. I'll follow up shortly

[Voxelr]

Ok, here's what I was able to gather

1      87.5
2      197.5
3      0
4      197.5
5      82.5
6      0
7      110.6
8      0
9      1.47
10      0

Small board
OA      83.8
IA      197.5
B-A/B   0
IB      197.5
OB      82.5

Big board
OA      1.45
OB      112.2
G      0
B+      197.5

[Paul Birkeland]

That's pretty informative.  Half of the 6080 isn't conducting, or being allowed to conduct potentially.  Do you have a different 6080 to try just to rule that out?  The +80V of bias on that half of the 6080 should result in enormous current draw, but perhaps there's something amiss with the 6080 that isn't allowing it to work.

[Voxelr]

Dang, ok, a tube problem would make sense considering it seems like one of the few parts to likely age out. I don't have any replacements off-hand, but I was considering rolling a new tube or two before this issue. So, I'm not that opposed to just buying a new one anyway. Is there a great way of diagnosing a tube problem at home, or does it just boil down to try a new one and see if it works? It would be nice to gain some confidence on a bad tube before making the financial investment, but if not, then it is what it is.

[Voxelr]

Actually, I guess replacement RCA 6080's are cheaper than I thought. I might just eat the cost on one to have something to A/B test with here.

[Paul Birkeland]

I think it's a good idea just to rule that out.  There are some pieces inside a 6080 that can come dislodged and prevent one half from operating from a very hard jarring, but I've also dropped 6080s on the floor and continued to use them with no issues.  This kind of issue isn't what I would expect from a tube that's exhausted, it's more like some kind of internal damage.

[Voxelr]

Yea, seems a bit odd to me too as the unit just lived on my desk when the issue surfaced. Anyways, I'll order another 6080 to see if that solves my problem. I'll let you know how it goes. Thanks for the help Paul, I genuinely appreciate it.

[Voxelr]

I'm still waiting on my replacement to arrive, but just wanted to update the thread here. I did a closer visual inspection of my current 6080, and found that this wire feeding into pin 6, connecting into terminal 9 looks pretty clearly busted. I'd call that a pretty conclusive root cause of my problem.

[Paul Birkeland]

If you thwack on it just the right way, maybe it will pop back into place

(No, don't try to do that!)

[Mucker]

I'm still waiting on my replacement to arrive, but just wanted to update the thread here. I did a closer visual inspection of my current 6080, and found that this wire feeding into pin 6, connecting into terminal 9 looks pretty clearly busted. I'd call that a pretty conclusive root cause of my problem.

Interesting design to put the fuse inside the tube ....... whodda thunk? 

[Voxelr]

Haha, if only this was as easy to repair as a normal fuse replacement. It's kinda frustrating that the only thing stopping this tube from working is, like, a 1mm gap on a tiny little wire. Oh well, guess I have a new desk ornament now.

[Voxelr]

Ok, great news: I dropped in the new tube today, and the amplifier is back to working condition! Thanks for the help on the thread here. I'm very glad to be listening through my Crack once again