Blown Tube [solved]

[squirreldude]

Hello all,

I just finished a lot of troubleshooting and got my crack powered up for the first time! I was admiring it for nearly 20 seconds before the pretty, orange glow of the power tube turned into a bright blast. Something in the tube popped and I unplugged the thing before there was too much damage. The fuse is fine but I'm not sure how I should proceed. Should I scrap the tube now? Does this qualify for a replacement? How could I go about testing the 6080 with my multimeter to see if it really is toast? I don't have any other tubes, so I'm dead in the water for now.

Thanks,
Karl

[Doc B.]

We don't know yet if the tube was bad or something was miswired that caused the tube to arc. We can send another tube ([email protected]), but go back and do your resistance measurements again to see if anything else was damaged before you plug another tube in.

[squirreldude]

Wow, Doc I shouldn't be surprised but you called it. I ran the resistance checks again and discovered there is something else going on in addition to the blown tube. The unit checked out fine before I powered up, but now I'm not reading anything at terminals 1, 2, 4, and 5. I'll attach the full resistance check below and a picture of the setup. What do you figure it could be? I'll have to add it to my replacement parts order before that ships.

Note that I have installed the headphone jack mod in the sticky of this crack forum. I also have jumpers between terminals 22, 17, and 11 so all these spots are properly grounded (due to powder coating). Correct me if this is a mistake, but I thought they should all be connected by the bare transformer bell if it weren't powder coated.

Terminal     Manual        Mine
1                 *                 N/A
2                 *                 N/A
3                 0 ohms       0.1 ohms
4                 *                 N/A
5                 *                 N/A
6                 2.4K ohms   0.1 ohms
7                 2.9K ohms   2.93K ohms
8                 0 ohms        0.1 ohms
9                 2.9K ohms   2.925K ohms
10               2.4K ohms   0.1 ohms
12               0 ohms        0.0 ohms
13               * ~270K      last read at 280K ohms and falling
14               0 ohms        0.1 ohms
20               0 ohms        0.2 ohms
22               0 ohms        0.4 ohms
           
B3               2.9K ohms   2.93K ohms
B6               2.9K ohms   2.926K ohms
RCA             0 ohms        0.1 ohms
Center Pins 90k-100k     102K ohms and 97K ohms

[Paul Birkeland]

Can you run the Crack without the 6080 and do voltage checks?  (Just terminals 1-5)

I don't see anything alarming in the resistance checks.

[squirreldude]

I just tried some voltage checks without the tube and didn't read anything at all for terminals 1-5.

[Paul Birkeland]

Perhaps the fuse popped?

[squirreldude]

Nope, the fuse was fine. When I powered up for the voltage check, the input tube up front was glowing. I also tested the terminals on the transformer just to make sure it was really taking power.

I checked it again tonight and noticed some different behavior. I'm reading the proper resistances at terminals 1-5 now and I have some new voltages to report. Remember, these are without the power tube plugged in.

T1: 92.6V
T2: 224.5V
T3: 0
T4: 224.0V
T5: 95.0V

I am wondering if it was just operator error the first time around. Do these look normal? I believe T2 and T3 are unusually high, but does that have something to do with the power tube being unplugged? Let me know if there are some other voltages/resistances you think will be helpful in tracking this issue down.

Thanks

[Paul Birkeland]

Well, this is good news!  Your power supply is working, and your 12AU7 is working properly.

Yes, your voltages are a little high because the 6080 isn't in there hogging all the current like it normally does. 

[squirreldude]

Well if that seems right, I'll just hang tight until the fine folk at BH support can get me a tube in the mail. What a bummer, but I hope the tube really was the only problem. I'll report back later.

[squirreldude]

Solved the problem. It was the power tube.

I sent an email to bottlehead replacement parts on Monday and haven't heard anything back yet. Should I expect confirmation that they got my request for replacement parts? Luckily, I received an order of other tubes today and they are working so far. There was no arc this time and the voltage checks went fine. I was hearing a lot of static after the amp was on for ~1 minute, but swapping the input tube for another has fixed that issue as well. It might need to be cleaned or broken in, but I'm kind of surprised that both of my stock tubes caused me problems. Oh well, at least it works now!

[Paul Birkeland]

A little bit of static can be from a tube with oxidized pins, or a tube that just needs to run for a few hours.

[Mordicai]

Solved the problem. It was the power tube.

I sent an email to bottlehead replacement parts on Monday and haven't heard anything back yet. Should I expect confirmation that they got my request for replacement parts? Luckily, I received an order of other tubes today and they are working so far. There was no arc this time and the voltage checks went fine. I was hearing a lot of static after the amp was on for ~1 minute, but swapping the input tube for another has fixed that issue as well. It might need to be cleaned or broken in, but I'm kind of surprised that both of my stock tubes caused me problems. Oh well, at least it works now!

Had the same problem Squirreldude. Nothing when I first powered up, then the power tube powered up but no sound; then the tube blew. Tube looked bad when the kit arrived so I had already ordered a replacement on ebay. Put in a new tube and have been rocking all week. Sent an e--mail to BBC like you but it has been a week with no reply.  Looking forward to the Speedball arrival.

[squirreldude]

I think I need to correct my previous post. My second input tube started out fine, but has been giving me the same static sound after a few hours of listening. It sounds more like a record scratching than white noise. I've heard it with two sets of RCA cables, different sources, and different headphones too. Should I let the tube run for a while or does it sound like a grounding issue?

Sent an e--mail to BBC like you but it has been a week with no reply.  Looking forward to the Speedball arrival.

Glad to see I didn't fall through the cracks alone or something. I have the Speedball sitting on my workbench now but I want to make sure the stock build is in 100% working order before installing the upgrade.

[Paul Birkeland]

If two tubes are giving you the same issue, and it happens after the amp has been on some time, this is very likely thermally related, and it would be a good idea to go through and reflow all your solder joints.

[Grainger49]

A little bit of static can be from a tube with oxidized pins, or a tube that just needs to run for a few hours.

Paul means to insert and extract the driver tube 10 times.  This cleans the tube pins and the socket at the same time.