Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: sfojws on November 27, 2021, 09:25:10 AM
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After listening to the stock Crack for three weeks, I set out to install the Speedball mod. After installing the small PC board, there was no audio in the right channel. Reheating the center terminals of the of the MJE-350 transistors resolved the problem.
Now, I'm having difficulty with the large PC board. Resistance checked out as specified in the manual. Voltage readings, at the terminals were:
OA, 119 V
OB, 138.4V
G 0.1 mV
B+, 203 V
At first, all four LEDs were glowing. The voltage readings were close enough to those specified in the manual, so I set up the Crack/Speedball in the system, and there was no audio on the left channel. I disconnected the board, resoldered the middle terminals of the TIP-50 transistors, rechecked the solder joints (with magnification), and reinstalled the board. The resistance readings were again OL (over limit), and the voltage reading at OB then read 200 V, and the two LEDs closer to the 6080 tube did not glow. All of the other voltage readings were as at first.
What next step(s) would you advise.
Many thanks. I hope that the Thanksgiving holiday went well for you.
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I would think that half of the 6080 is not conducting. Perhaps reflowing the joints on the big board and the 8 pin socket would be in order. Don't worry about the hlmp-6000's for now.
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Thanks for the advice. Although there are a few burn marks on the PC board, from the repeated soldering, both channels are coming through! There is a slight attenuation of the right channel, which may be the source (Rudy Van Gelder recordings often are a bit left channel heavy), or a matter of burn-in for the circuitry. Nonetheless, it looks as if we have a winner.
All the best to you.
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Follow up on earlier problem: After reflowing the solder joints on the large PC board and the 6080 tube, the channel imbalance persisted, almost no audio from the right channel. I augmented a number of other solder joints. Curiously, the left channel was then attenuated. After further work on a few other solder joints, the channel balance appears to have improved, but now there is a persistent 60 Hz hum on the right channel. Obviously, I have overlooked something. Can you suggest any actions to attempt to resolve this? Thank you.
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Can you recheck your voltages?
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Hi Paul - Thanks for following up on this. I ran a resistance check, per the Crack manual, and all readings were as specified.
Voltage readings were also taken with the Speedball circuitry in place, and were as follows:
Terminal 1. 61.6 V
2. 204 V
3. 0.2 mV
4. 204 V
5. 0.2-1.4 V (variable)
6. 0.1 mV
7. 130.2 V
8. 0.1 mV
9. 0.1 mV
10. 0 V
So, the readings on terminals 5 & 9 were significantly off expected levels, so I messed up somewhere. What do you see as the next step? Many Thanks.
JS
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Hello again - Following your "socratic" lead, I reflowed the solder joints at terminals 5 & 9, at the OB terminals on the two PC boards, as well as the MJE-350 transistor, the LED, and the lead of the 150K resistor on the small board. The voltage readings at terminals 5 & 9 were then 76 and 113 volts, respectively, and all other readings were within 1% of those that I posted a bit earlier. The hum on the right channel was greatly reduced, but now there is no audio on the left channel. Now, I'm leaving the amp alone, and will determine what further thoughts you have.
Grazie mille.
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I definitely would not recommend resoldering any LEDs unless you know with some certainty that the solder joints holding it in are problematic. The LEDs are small and require very little heat to solder properly, but they can be overheated and damaged.
Can you recheck the voltages on the small board with no 6080 in the socket?
When building the Speedball, we have you check the small board prior to installing the big board, did your amp pass that check at that time?
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Thanks, I'll do that, and send you the results. To be certain that I'm interpreting the direction correctly, shall I run the voltage check with only the 6080 removed, and the 12AU7 in place?
I did perform the checks, per the instructions in the manual, on the small board, prior to listening, or installing the large board. The readings were good, and the amp worked as expected. After installing the large board, there was no audio on one channel. The advice from one of your colleagues was to reflow the solder joints on the large board. At first listening, both channels worked, but the volume was noticeably attenuated on one channel. I was occupied with other life issues for a couple of months, before resuming attempting to get the amp working last week.
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Here are the voltage readings, with the 6080 tube removed:
Terminal 1. 62 V
2. 227 V
3. 0
4. 227 V
5. 75.2 V
6. 0
7. 57.8 V
8. 0
9. 1.5 V
10. 0
Many thanks.
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Can you post some build pics?
The presence of DC voltage at terminal 7 with no 6080 installed would have me concerned that there's a miswire in the stock build.
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Hi Paul - I just attempted to send a series of five photos, which I had to copy to the desktop, in order to allow me to use the "Choose File" command. As it has turned out, the jpg files in the photo album seem to be converted to jpeg files on the desktop, and that format cannot be sent via the forum platform. I'm attempting to find a workaround, in order to send the photos.
Have you encountered previous occasions of forum members encountering this dilemma? Is there a technique that worked out?
Many thanks.
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Can you just change the file extension to .jpg?
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Not being familiar with changing file formats, I'm working on a method to do that. The first attempt is a conversion to pdf format. If this doesn't work, I'll see if it's possible to convert to jpg. Ironically, the files in the Photo program (app) stores the photos in jpg, but I have to copy them to the desktop in order to send them. The files that then appear on the desktop are converted, somehow, to jpeg. AARRGGHH!
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What device are you taking the photos with?
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Do you have a loose black wire on the headphone jack? I don't think that would be responsible for everything that's going on with your amp, but would definitely be a place to start.
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It's an iPhone SE, 2014 vintage. The newer one (2017) was being charged at the time. Resolution trouble?
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Hi Paul - I had suspected that as a potential problem, so I had reflowed that joint last week, returning to a better brand of solder (Kester, which I had used on the Moreplay & Reduction).
Please let me know if you have a problem with the photos. It may be possible to send the files in a different format. I haven't had need to try that in the past, but it appears to be doable.
JS
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I suspect your issue is going to come down to broken wires (the teflon jacketed ones) or solder joints. I don't see anything super obvious there.
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Good morning Paul - Thank you for taking a good look. Yes, I was also flummoxed, after going through the manuals for the basic build and the upgrade, step by step, to try to spot an error in wiring.
Would a continuity (resistance) check on the wires help uncover the possibility of a broken wire? Although it's like looking for the proverbial needle in a haystack, if it's a possible method of spotting a broken wire, it would be worth the effort.
JS
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With your kit, you may find that you can poke around it with a wooden chopstick while it's running and a pair of cheap headphones plugged in to activate either pops or flashing LEDs, and that can help narrow down your focus a bit.
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Re my question regarding the phone, I was just thinking it might be easier to post the images to the forum right from the phone to avoid the file name issue. Or as was suggested you might just try renaming the files from .jpeg back to .jpg. Typically you can go into a file browser, click on the file (right click for Win) and choose rename. Jeez I just noticed that Win has added an extra "Show more options" step to get to Rename. Funny how after 40 years of personal devices graphics apps still can't carry on a conversation without an interpreter and guys still justify their jobs as programmers by moving shit around from where it has been for the past ten years so you can't find it.