Bottlehead Forum
Bottlehead Kits => Mainline => Topic started by: AllanMarcus on April 10, 2018, 05:21:00 PM
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Hello,
I just finished all the soldering, and passed the resistance tests. I have a problem with the voltage check, and I'm hoping I can get some help narrowing it down.
The only out of spec results are breg and kreg on the B side
A side
breg: 221
kreg: 10.66
B side
breg: 283
keg: 1.23
It appears I have a problem on the B side, but I'm not sure what I need to do beyond the obvious reflow and validate the build wth the instructions.
Thanks,
Allan
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Allan,
Would you post a close up pix of your pc boards and an overall pix of the entire amp underside?
I would be glad to compare to mine...
Alex
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Thanks.
A little more info. I was able to set the bias to 145 for both sides.
All 4 LED glow
I reflowed all the joints on all three boards.
Still have he same issue. Are there any other measurements I can take to help isolate this? Should I swap the a and b boards?
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Juat a thought....is this the board that you mis-soldered the MJE5731A in?
Alex
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Hard to say. Tonight I will swap the a and b boards and see if the issue follows the board. That will help narrow it down.
I'm also going to print the manual and go though it again, which time checking off items. I would prefer is the manual were a PDF with check boxes, but this is the next best thing. I just hate killing trees.
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Allan
I looked at your pix and I didnt see any misplaced parts as best as I could tell.
The only comment I would make is some of the solder joints on the center board look like they might not be soldered well on the topside?
Dont know if this is it or not?
But most of the solder joints will have good joints on both sides...
Swapping the boards is something I would do...
Hopefully Paul or Doc will chime in soon as well....
Alex
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Allan
I looked at your pix and I didnt see any misplaced parts as best as I could tell.
The only comment I would make is some of the solder joints on the center board look like they might not be soldered well on the topside?
Dont know if this is it or not?
But most of the solder joints will have good joints on both sides...
Swapping the boards is something I would do...
Hopefully Paul or Doc will chime in soon as well....
Alex
Thanks. The one joint you circled is on the side that is working :-)
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You could try plugging in a different 12AU7 and see if that changes anything.
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Low voltage on Kreg and high voltage on Breg do indeed indicate a problem. What is the DC voltage on the 220K resistor lead closer to the center of the PC board?
Double check that the 431 regulators are where they are supposed to be and not accidentally swapped with a PN2907.
Also be sure that the connections at pins 2 and 7 on the 12AU7 socket are nice and solid on both ends (see page 62). Just be sure these connections are all tight.
It's also possible that there's an issue with some of the heater wiring on the 12AU7. Do you see a glowing dot or two on both of the plate structures inside the tube?
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Thanks CB. I will check all those things first.
The voltage on the 220’s is the same as for
There are four pm2907s on the C4S boards.
Thanks doc. Tried another tube and same issue.
I swapped the C4S boards, and same exact readings, so I don't think it's on those boards. If CB's ideas don't pan out, I'm gonna walk the manual again and check everything item.
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Well, I found my first error. Top of page 58. I soldered the red wire to b4,but did not route it to B5
Hopefully that’s it, but I will continue to check the rest of the manual.
Ug.
Update: that was it! Bias all done, and waiting for the transformer to cool to flip it over and try the final instruction from the manual - throw on some music!
I don’t understand why you guys didn’t notice this in the pictures :-)
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http://www.instructables.com/id/Homemade-Xray-Machine/
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http://www.instructables.com/id/Homemade-Xray-Machine/
Which socket on the mainline do the x-ray tubes go into?
OK, seriously. I have a question. The heat shrink the got fitted over a few wires. Do they just shrink over time by themselves?
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Wow!!
I was wondering why Doc posted that X-ray machine link!!! LOL
I just looked at page 58!! Ha!
Thats a good one...
So how does it sound / work??
I got out 4 amps yesterday and listened to each for 30 minutes...and all are good, BUT
when I got back to the mainline it was subjective heaven.
Alex
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Wow!!
I was wondering why Doc posted that X-ray machine link!!! LOL
I just looked at page 58!! Ha!
Thats a good one...
So how does it sound / work??
I got out 4 amps yesterday and listened to each for 30 minutes...and all are good, BUT
when I got back to the mainline it was subjective heaven.
Alex
I really only got a few minutes with it because it was late and I had stuff to do before I went to bed. I'll get a little time tonight, then I'm out of town until sunday. Sigh.
From what I've heard, very good. I made a box that lets me plug into up to amps, and outputs to one headphone. This lets me switch between amps.
https://sites.google.com/marcusfamily.info/diynotes/my-stuff/balanced-switchbox?authuser=0
So far I can hear some difference between the Mainline and the Black Widow 2, but I haven't identified what that is yet. I think the mainline is a little smoother. Plus, from what I understand, the Mainline (and all tube amps) need some burn-in time.
Thanks for all your help.
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My point about the x-ray machine was that it would be pretty difficult for us to spot a miswire on a tube socket with PC boards blocking the view of the sockets in the photos.
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Yeah! I got that....
So when is BH going to offer a X-Ray Kit!!
lol
Alex
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X-Ray Audio (https://x-rayaudio.squarespace.com/about/)
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X-Ray Audio (https://x-rayaudio.squarespace.com/about/)
I don't know. Your humor seems a bit...transparent!
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Ha Ha, I saw through that one!
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I would have found that missing wire, but I wasnt using my NOS X-Ray tube.....
:>)
Alex
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Hey Allan..
So have you had a chance to listen to the amp yet..and what are your impressions?
I have been going thru my T1's and a backup set of tubes...and tonight I am trying my T90s...
I put a new set of earpads on them and new inner foam inserts...from Beyer...
Gosh these T90s that most folks think are too bright on the upper end work wonderfully with the Mainline.
I use Brian Bombergs "Wood" cd for my bass testing...and its about as good as it gets....very nice, accurate, tonality is very natural, musical...
Alex
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I finally got my A/B set-up, set-up! I can now easily switch between a Magni3, Black Widow 2, Crack, and Mainline. I'm focusing on comparing the SS to each other, and the tube amps to each other.
So far I've only compared the Mainline to the Crack with an HD6xx.
Crack: smoother. bass a bit looser
Mainline: Tighter bass. More byte/detail with the mainline, but not fatiguing.
Mainline is a bit more forward. More presence with the mainline. Maybe better staging
Mainline is just clearer and more enjoyable.
The Crack is very tube dependent. I'm using a Siemens Silver Plates 12AU7 and a NOS Tung-Sol 7236.