Yes I am using the 125 tap. Wall voltage is around 120, fluctuating a bit but no more than a few volts. That OT works great, nothing against to say !
Thanks for the kind words! Spending a bit of time with my loved ones since I did put a lot of efforts and time recently on this build, and watching vids on chasing hum in a tube amp
I will play with different spots for the OT gnd and and see/or mostly listen to the difference
fred.violleau wrote: ↑Wed Nov 11, 2020 2:57 amHere are the voltages i get :
B+ : 441.4V
B+1: 440.3V
B+2: 419 V
B+3a: 378.7 V
B+3b: 305 V
B+4: 316.8 V
B+5: 309.1V
...
FX LOOP - 12AX7
V3A 1 : 305 V
V3A 2 : 18.81v
V3A 3 : 37.72 V
V3B 1 : 233.8 V
V3B 2 : 0.6mv
V3B 3 : 1.731 V
Fred, if I understand the correspondence between the voltages you list above and the locations on your layout, I recommend some adjustment to the loop supply as shown below to get the loop tube voltages in line.
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Agreed, voltages are a bit high on the loop, I will try to adjust as much as possible. I though I needed 360v and 280v, are you sure on the second FX loop node ? where would that bring the voltages?
I don't know if I left enough room to play with these resistors though.. I'll give it a try!
After a couple hours of playing, I reviewed Tony and Matt Rae's recordings, not that I compare in talent to this guys in any way, but the caracteristics on the amp I built are closer to what Tony has. For the first time the bright switches are not to bright, and really add versatility. The overdrive is not super gainy, although when pushed (PAB + Mid Boost on the drive channel) push the strat into 80's heavy rock territories but not that compressed though. I would not caracterize the OD as smooth on this amp, it is super punchy, in your face and very mid focused and the note definition is very articulated (almost scary at times, because you can't hide with an amp like that)
I just realized that I did not set the trimmer on the OD channel.
#183 layout references the wiper 22k above ground. Does that means the resistance between 3 and 2 is 22k if 1 is ground?
Another thing I noticed is the bloom is hardly perceptible, compared to the others build (specially the bluesmaster). I can't play too loud either in a small room, so that may not help.
I don't know if it is because of the EL34, but it feels a lot stiffer than my other builds. May try to bias the amp with 6L6s and see which one I prefer.
I still have to play with the PI trimmer here, because it helped on the bloom of my other builds.
I will report as soon as the d-lator voltages are adjusted with a complete list of the voltages and internal settings
fred.violleau wrote: ↑Tue Nov 17, 2020 12:57 amAgreed, voltages are a bit high on the loop, I will try to adjust as much as possible. I though I needed 360v and 280v, are you sure on the second FX loop node ? where would that bring the voltages?
I don't know if I left enough room to play with these resistors though.. I'll give it a try!
Typical supply voltages for the D loop are 260V for the CF driver, and 360V for the recovery stage. The required dropping resistor between the two will be 100k (like the stand-alone loop) when you get 360V on B+3A. I don't know where your B+2 (screen) is now that you have your wiring error fixed, but if it is around 440V the resistor from B+2 will be about 33k. You should be able to change those resistors from the top of the board, and note that a 1W rating will be more than adequate.
fred.violleau wrote: ↑Tue Nov 17, 2020 12:57 amAgreed, voltages are a bit high on the loop, I will try to adjust as much as possible. I though I needed 360v and 280v, are you sure on the second FX loop node ? where would that bring the voltages?
I don't know if I left enough room to play with these resistors though.. I'll give it a try!
Typical supply voltages for the D loop are 260V for the CF driver, and 360V for the recovery stage. The required dropping resistor between the two will be 100k (like the stand-alone loop) when you get 360V on B+3A. I don't know where your B+2 (screen) is now that you have your wiring error fixed, but if it is around 440V the resistor from B+2 will be about 33k. You should be able to change those resistors from the top of the board, and note that a 1W rating will be more than adequate.
Martin,
I know this is basic stuff, but I'm trying to get my head around it and seem to be missing a critical part of the equation.
To simplify this I was looking at voltage drop from V3a to V3b...360V-260V = 100V. Assuming that the current draw is 1mA for half of the triode, using the formula R = V(drop)/I ...R = 100/0.001 = 10K. Easy enough since it's dealing with half of a triode.
But when looking at 440V on B+2 and you want to see 360V on B+3a, is the draw the sum of the downstream tubes...6mA? If I do that math, I get 13.3K as the resistor. Clearly, there's something (or several things) that I'm not considering and I'd like to understand this better.
Vertigo wrote: ↑Tue Nov 17, 2020 8:14 pmI know this is basic stuff, but I'm trying to get my head around it and seem to be missing a critical part of the equation.
To simplify this I was looking at voltage drop from V3a to V3b...360V-260V = 100V. Assuming that the current draw is 1mA for half of the triode, using the formula R = V(drop)/I ...R = 100/0.001 = 10K.
Check that, it's 100k
Vertigo wrote: ↑Tue Nov 17, 2020 8:14 pmBut when looking at 440V on B+2 and you want to see 360V on B+3a, is the draw the sum of the downstream tubes...6mA? If I do that math, I get 13.3K as the resistor. Clearly, there's something (or several things) that I'm not considering and I'd like to understand this better.
This is a separate branch that comes off the screen node and only supplies the loop. Total current is about 2.4 mA. The first dropping resistor would be (440-360)/0.0024 = 33.3k.
Vertigo wrote: ↑Tue Nov 17, 2020 8:14 pmI know this is basic stuff, but I'm trying to get my head around it and seem to be missing a critical part of the equation.
To simplify this I was looking at voltage drop from V3a to V3b...360V-260V = 100V. Assuming that the current draw is 1mA for half of the triode, using the formula R = V(drop)/I ...R = 100/0.001 = 10K.
Check that, it's 100k
Vertigo wrote: ↑Tue Nov 17, 2020 8:14 pmBut when looking at 440V on B+2 and you want to see 360V on B+3a, is the draw the sum of the downstream tubes...6mA? If I do that math, I get 13.3K as the resistor. Clearly, there's something (or several things) that I'm not considering and I'd like to understand this better.
This is a separate branch that comes off the screen node and only supplies the loop. Total current is about 2.4 mA. The first dropping resistor would be (440-360)/0.0024 = 33.3k.
My apologies...that first example was a keystroke error...the little spreadsheet I made and my paper version both say 100K
I did replace the 56k resistor with a 100k 2watt found in my stach, but I am missing a 33k resistor.
Found a 37k which is too much. I have a 27k which is too little or maybe I could try to fit in 2x68k in parrallel but space is tight there..
Played with the trimmer for the OD and it brought more gain.
Played with the trimmer at the PI, and it fattens the sound and burry the E and B string, or clean up the sound and bring these forward.
I am not sur which one I like better, so may play some more with this one.
Not settled on the speaker choice either so this one will definitely vary.
Question : is it me or the more the amp cooks, the better it gets?
I have realized that with all my builds. It seems like the sound of the amp is evolving and I have trouble understanding if it is me and my playing that adjust to the amp, or the components and voltages that settle...
I had the amp run all day yesterday, monitoring the new voltages with the resistor update and by the end of the day, sound was different not by much, but amp now starts to bloom a little, which it did not at the beginning.
Some burn-in time is widely thought to cause some components to change subtly (mainly capacitors, I would think), and I believe many boutique builders make it a standard practice. There is probably some of you getting used to it going on too. In my experience new amps seem overly bright at first, and after just a few of hours use seem to mellow a bit.
talbany wrote: ↑Sat Oct 26, 2019 10:17 pm
24. 250Pf Snubbers ala 102.
Going back to the original post. Hope that's ok. I built a 183 and I recently changed the snubbers from the 183 schematic values of 25pF to the 102 values of 250pF like Tony did here. I think 250pF takes off some of the top end fizz of an overdriven single coil pickup. So I have three questions:
1) Tony, why did you choose to go with 250pF snubbers?
2) Is it possible that the 183 schematic is incorrect w.r.t the snubbers and that 183 really had 250pF caps there? To me, 25pF doesn't make sense.
3) Are there any other known Dumble amps that use 25pF snubbers?
@donvan, interesting comment as this build sounds a bit darker to me. It's the first time I need to use the bright switch on the clean side, because on its own, it is dark, almost jazzy. The OD side feels very mid focused, and not harsh or fizzy at all.
I will try to capture some sounds with humbuckers, it really kicks in the but when paired with the 2x10 celestions, brings the mid forward, tames the highs a little and gives a nice tight low end.
I heard Joe Bonamassa say that speakers could make or break a dumble, and I tend to agree with this build, it feels to me the celestions seems to be a good pairing. I liked the WGS ETA90, but they are a bit bright and mid scooped compared to the celestions.
Hi Fred,
It is interesting that your build is very dark sounding. Not sure if you did a 102 or 183 or somewhere in between. I do not consider my 183 dark sounding at all. I never use the bright switch on single coil pickups with this build. With humbuckers I do use it at times but mostly not.
Also, the snubber caps that I am referring to only affect the OD circuit.
