Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: BrettMatthews on January 30, 2016, 06:15:33 AM
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Hey guys, I just finished installing my speedball into my crack which was working great before. I am just having one small problem now, my voltages at terminals 1 and 7 are out of spec, all other voltages are fine. Voltages are as follows:
1 - 116
5 - 101
7 - 127
9 - 117
So my B side is is right around the range of the upper specs, but my A side is definitely out.
All LEDs light up (the ones on the small board arent as bright as the rest though, not sure if that is normal or not), I have triple checked resistors and they are all correct, and I have gone over most of the solder joints.
Any suggestions are greatly appreciated.
Thanks
Matthew
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Does the voltage at T1 change if you run the Crack without a 6080?
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Yes the voltage does change if I remove the 6080:
1 - 91
5 - 78
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It shouldn't, is the B+ wire from the big board going to terminal 1 or terminal 2?
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The B+ wire from the big board is going to terminal 2.
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The connection at B4 is very close to touching B3, if they were touching with a 6080 in the socket, that could have some unpredictable results.
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It must have just been the camera angle as it definitely wasn't touching, but for good measure I trimmed it and retested but there was no change.
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I'd go over your solder joints then, both on and off the boards. The functioning of the small PC boards is independent of the large PC board, so if running both tubes causes odd performance in the 12AU7, then there may be a marginal joint.
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So I've had a chance to work on this some more but still haven't been able to solve my issue.
I have tried swapping the small boards and the problem did not follow the small board so it's not an issue with those, and I have rechecked the solder on 1l and 1u and the tubes that those spots are going to and that didn't help either. The voltages did come down a little bit after I reflowed the joints on the large PCB (good side is about 90 and bad side about 108) but the one side is still out of tolerance. Any other thoughts or spots I should look to?
Edit: reflowed the solder on the big board again, no change.
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Such a problem could also be caused by weak heater voltage. This is the red/black twisted pair of wires that feeds from power transformer terminals 4 and 5 to B7/B8, then down to A4/A5/A9. Removing the 6080 removes most of the load on this feed, and could allow for the 12AU7 to properly heat if there's a marginal connection here.
It's possible to measure this voltage, but I would recommend reheating ALL of the joints mentioned above.
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Thanks again for the suggestion, sadly it still did not fix the issue. I reheated all of the suggested points but did not bring the voltage down at all.
Is there a chance this could be tube related?
Edit: Since you said it is possible to have these voltages I decided to give it a try and see how it sounds (work setup, e10, dt770 250). A couple things I noticed were the noise floor is quite high overall, and if I tap on the metal top plate I can hear it from the right driver, I hear a ting sound, but only really from the right driver. Not sure if this points to anything or not though.
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Set your meter to AC voltage, ground one probe (sometimes easiest to smoosh it under the solder tab at the #8 screw back by the IEC), then carefully measure the AC voltage at A4, then measure the AC voltage at A9.
This is very unlikely to be tube related since the 12AU7 works fine without the 6080 installed in the amplifier.
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Okay so the ac voltage measurements are as follows:
A4: 0.01vac
A9: 5.8vac
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There's a very slight chance that a different 12AU7 might give different results, but there isn't anything about the installation of the Speedball that would bring about these changes unless something fundamental to the circuit was disturbed or altered.
If at all possible, with the little board pulled up and out of the way, can you confirm your voltage at A8?
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Voltage at A8 is 0Vac.
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How about A3?
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A3 is 0 Vac as well.
Edit:interesting enough it seems that the voltage at pin 1 is sitting at about 101V today which puts it right about in spec. Pin 7 is still a bit high at 119V though.
One other thing I did notice is that when the amp is upside down I didn't hear any noise if I taped on the baseplate, but once I flipped it back over tube side up it came back. Also when listening I can hear small electric noise bursts everyonce and a while.
I also heard a pop when I turned on the amp with headphones connected (luckily no damage done to the headphones), I then checked the voltage on the jack at the ring and it started slowly started climbing and then jumped to 25v for a second then back down to 0v.
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A3 is 0 Vac as well.
These need to be DC voltage measurements.
One other thing I did notice is that when the amp is upside down I didn't hear any noise if I taped on the baseplate, but once I flipped it back over tube side up it came back. Also when listening I can hear small electric noise bursts everyonce and a while.
The not about having the plate flipped over suggests a bad solder joint. The electric noise bursts indicate that you own a cell phone.
I also heard a pop when I turned on the amp with headphones connected (luckily no damage done to the headphones), I then checked the voltage on the jack at the ring and it started slowly started climbing and then jumped to 25v for a second then back down to 0v.
The amp will thump audibly when you turn it on and headphones are connected, there isn't anything unusual or alarming here.
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These need to be DC voltage measurements.The not about having the plate flipped over suggests a bad solder joint. The electric noise bursts indicate that you own a cell phone.The amp will thump audibly when you turn it on and headphones are connected, there isn't anything unusual or alarming here.
I will grab the DC measurements tomorrow morning, any others to check right now?
Phone noise makes sense as it was being driven off my phone. The sound I heard when I turn it on isn't a thump, I'm used to heading a quiet thump with my o2 amp, this is a plus pop,loud enough that I was worried it damaged my headphone, was more than one pop and just from one side (left I think).
I will double check some of the grounds, can you think of any in particular to check?
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A3 and A8 are both about 1.6 Vdc
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Can you remove the small PC board on the offending side and put the 22K resistor back in, then recheck your terminal 1 voltage?
-PB
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I will give that a try this weekend when I should have some time to work on things.
I'm starting to think that maybe a ground came loose while transporting the amp from my home to my work (have nice pace soldering gear at work). I'll retouch all the grounds this weekend too.
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Okay so good news! Looks like I found the bad ground (sounds the same upside down or right side up), not sure exactly where it was I was just touching up a few spots then tested things out and it seems to be good! A1 and A7 are still higher than the other side but are within spec now at least.
It's still recommended to connect the non used pins on the 1/4" Jack to ground correct?
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It's still recommended to connect the non used pins on the 1/4" Jack to ground correct?
There's certainly nothing wrong with doing this to a stock Crack or Speedballed Crack.