Hello,
I'm having trouble with my UberTuber build. It passes sound, but sounds muffled/awful. I followed the BOM without knowingly making any modifications. The resistors and capacitors were all checked with a multimeter immediately before placing the component on the board. The volume knob and boost switch seem to do something. The other knobs don't seem to do much. The plate voltages (T1 and T2 below) are abnormally high, which suggests this is the problem. Unfortunately, I don't really know how to read a schematic to figure out which parts could be causing the issue. Any and all help is greatly appreciated!
Solder side:
(https://i.imgur.com/IGPQM6g.jpg)
Component side:
(http://i.imgur.com/kOavcVu.jpg) (https://imgur.com/kOavcVu)
Test box voltage = +18.09
T1 = +17.54
T2 = +17.37
T3 = +11.5
T4 = +6.47
Thanks!
Darin
Your plate and cathode resistors are correct. Your heater voltage is slightly high at 6.47v but that may not be a concern. The bad plate voltages may indicate an issue with the tube itself. Please link to where you purchased it.
I bought this one... https://www.ebay.com/itm/NOS-6111-dual-triode-subminiature-vacuum-tubes/290862897028?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Quote from: DLW on September 13, 2018, 06:54:44 AM
I bought this one... https://www.ebay.com/itm/NOS-6111-dual-triode-subminiature-vacuum-tubes/290862897028?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Hmm. There's no branding on the tube and the listing does not indicate a manufacturer. How about on the actual tube you received? Is there a company name or any other writing on it besides 6111?
The writing is on the bottom side of the tube :|
This is what I can read: 6111.???.66404
I'll contact the seller to ask for more info about the tubes.
I finally heard back from the eBay seller...they have no idea who manufactured the tubes. Probably not the highest quality. Does it make sense to replace the tube? Is there a way to test a tube before it goes on the board? I'm not even sure that I didn't damage it while soldering. Are these tubes easy to damage that way?
I purchased my tube from the same place and my build is working. Not saying that your tube is good, just saying mine was ok.
Well disregard that. I plugged mine in and it worked then I remembered I needed to set the trimmer. My voltages are running the same as yours. This can't be a coincidence that my voltage at T1 and T2 are almost the same. I'm pulling mine and getting another one from a reputable place.
That's good to know. The seller was actually very reasonable and responsive. I don't blame him at all. I just ordered a Raytheon tube. Only 4 dollars more than the no name brand. Maybe that will fix it...
Please post your outcome. Thanks.
Genuine Raytheon tube fixed it. Pedal is fully operational now. Thanks for the help.
That's great to hear. Thanks for the update.
I'm going to tag onto this thread to ask if the following voltages are ok:
V+: 17.97V
T1: 15.28V
T2: 13.07V
T3: 11.59V
T4: 6.34V
T1 and T2 are a bit high, no?
Tube from Smallbear.
I'll also note that SAT and CUT do not seem to make noticeable changes to the sound. Although LVL and DRV make it louder or quieter, things seem to be staying fairly clean sounding.
I have no real experience analyzing tube circuits, but here is a somewhat reckless wild guess as to what's going on in my build:
With my higher plate voltages, are my triodes operating at lower than expected gain, resulting in my cleaner than expected sound, with a signal not high enough to push the second triode very hard and failing to clip noticeably at the saturation control?
T2 is a bit high but not too worrisome. T1 is a problem though. I start by increasing the plate resistor on that one from 100k to 150k. You could lower T2 by increasing its resistor to 120k. Your V+ and heater are spot on so it's just wrangling those plates in.
Maybe for the next batch I should put trimmers in place of resistors for the plates. I never really had a problem with my own set of tubes achieving proper bias but of course people are getting them from all over the place. So, it seems like an obvious improvement to the design.
My voltage are off as well. Everything seemed to be working as far as I could tell. Haven't had a chance to box mine up yet. I'll see if I can get the voltages posted when I get a chance.
Quote from: madbean on October 16, 2018, 12:03:37 PM
T2 is a bit high but not too worrisome. T1 is a problem though. I start by increasing the plate resistor on that one from 100k to 150k. You could lower T2 by increasing its resistor to 120k. Your V+ and heater are spot on so it's just wrangling those plates in.
Hmm...
I made the changes to 150k and 120k.
Now I get:
V+: 17.97V
T1: 14.39V (down from 15.28V)
T2: 13.68V (up from 13.07V)
T3: 11.59V
T4: 6.32V
Well I don't know how your voltage could have gone up, haha. That is strange indeed. Can we see a pic of the top of the board, please? Let's see if we can figure out what's going on here.
Quote from: madbean on October 18, 2018, 05:05:34 AM
Well I don't know how your voltage could have gone up, haha. That is strange indeed. Can we see a pic of the top of the board, please? Let's see if we can figure out what's going on here.
Is this the top?
(http://i.imgur.com/81SuEgN.jpg)
This pic was taken before I swapped the resistors. Also, there is a piece of foam tape insulating the toggle from the back of the daughter board (in case that isn't clear).
Insofar as I can tell, that looks right. Except maybe R4 which does not appear to be 22k but I can't quite make out all the color bands (not sure if the 1st band is blue, or black but it should be red, red, black, red, brown).
The tube you got from smallbear, is it the 6111 or 6021?
I probably should have suggested socketing those two plate resistors but instead made an educated guess as to what would bring it into proper bias.
Quote from: madbean on October 18, 2018, 05:51:35 AM
Insofar as I can tell, that looks right. Except maybe R4 which does not appear to be 22k but I can't quite make out all the color bands (not sure if the 1st band is blue, or black but it should be red, red, black, red, brown).
I'll check that one out when I get home.
Quote
The tube you got from smallbear, is it the 6111 or 6021?
It's the 6111. Thomson brand, if I recall correctly.
Quote
I probably should have suggested socketing those two plate resistors but instead made an educated guess as to what would bring it into proper bias.
I'll probably will socket them before making any further changes.
Just checked my R4. It is 22k (21.98k measured). Weird shadow plus thin paint sure did make that look incorrect in the other pic. Here is a closer view (which only looks a little better):
(http://i.imgur.com/4CjUxZ7.jpg)
It is interesting that the T2 voltage went up with the higher plate resistor. Apparently, that resistor changed the current quite a bit. I suppose I could fuss with the cathode resistors. Maybe I should just try another tube....
Don't know if this helps but I just measured my voltages TP2 seems to change with the position of the drive pot. Assuming that's normal? I also have a Thomson brand tube from Small Bear, 6111 printed on the glass. Everything does seem to be working, CUT & SAT pots included. Both subtle effects but they are there.
VC 18.34
TP1 14.54
TP2 (DRIVE @ 0) 13.08
TP2 (DRIVE @ MAX) 14.85
TP3 11.47
TP4 6.54
Like I said everything seems to be working and it sounds pretty good. Just unsure if plate voltages being high could cause a problem down the road? Like shortened tube life or something?
That actually is a good point. The Drive knob probably does change the input bias a bit going into the second triode which would explain small differences in voltage readings. I'll need to take a look at mine to verify but it seems to be the likely explanation.
I am a bit more concerned about the higher plate voltages some people are having. Like I said, I've built the UT at least 2-3 times and with different tubes and my results have been consistent. And, I've built different variations of this circuit with a 6021 and got similar results, IIRC. So, it does seem like the best thing to do is suggest people socket R5 and R8 to allows for fine adjustments. There is still a range of plate voltages that should work but I would really prefer people to get consistent results with what the build doc lists.
I will be placing another order for boards next month so I will go ahead and change those resistors to trimmers. I'm kind of kicking myself now for not doing that. But, the first time you do a new type of project there's always a bit of a learning curve.
I'm in the process of adding sockets for R5 and R8.
Quote from: BryGuy on October 19, 2018, 06:16:55 PM
Don't know if this helps but I just measured my voltages TP2 seems to change with the position of the drive pot.
That probably explains my increasing T2 voltage. I more or less centered the controls for my measurements by rough feel (no knob indicators).
Threw in some 180k resistors.
T1: 14.05V
T2: 11.30V
Should I just keep jacking that plate 1 resistor higher and higher?
220k:
T1: 13.57V
Quote from: EBK on October 20, 2018, 11:03:10 AM
Threw in some 180k resistors.
T1: 14.05V
T2: 11.30V
Should I just keep jacking that plate 1 resistor higher and higher?
220k:
T1: 13.57V
Definitely close enough. How is it sounding with the new plate voltages?
Quote from: madbean on October 20, 2018, 12:40:40 PM
Definitely close enough. How is it sounding with the new plate voltages?
I'll report in tomorrow on how it sounds.
I actually haven't listened to it since I clipped the original resistors out.
Ok, I've listened to it again. It is definitely much more gritty and crunchy now. I kind of feel that it is cutting too much high end though, even with the cut control at its minimum. With cut maxed, it is very dull sounding. I may try lower those plate resistors a tad to see if I like it a bit better. The saturation control is still barely noticeable.
Man, I'm sorry this is giving such trouble. The Sat knob should be very, very noticeable.
I will probably go ahead an order one of the 6111 from smallbear and compare it to mine. I still have the box of ones I bought from CE Distribution but I simply haven't had time to test each one. But, if I can pull out a good one I'll send it to you if we can't get your build sorted.
I double checked my sat pot. It appears to be properly connected and working as it should, other than not doing much for the sound. Seems that maybe the signal is too low there still? I might have to dig out my scope. Is adjusting the plate voltage merely adjusting the headroom without touching the gain (is this what "starved plate" means)? (Again, I wish I knew more about tubes....)
This weekend, fingers crossed, I hope to connect my scope and function generator to this circuit to see if I can confirm my suspicion that the output is too low for the saturation control to work (suggesting that the tube's gain is too low). Will report back. I'll also test with a higher voltage on plate 1. Although I can get it to distort by pushing that plate voltage down, I really need the saturation control to do more that it currently does to justify the extra knob. ;)
Ok, here are some results of testing with my scope and waveform generator.
Input is a roughly 100mVP-P triangle wave at 1kHz.
Is that a reasonable amplitude for a guitar signal?
The scope is measuring the top of the saturation diodes.
(http://i.imgur.com/hHrPiYwl.jpg)
This is with drive maxed. The output is 476mVP-P, not enough for the diodes to conduct at any setting of the saturation control. If the input is cranked up much higher, then the sat control works as expected.
I'd be interested in hearing what the signal is under these conditions with a different tube.
Are there any additional tests that you would be interested in seeing?