martin manning wrote: ↑Sun May 09, 2021 1:50 am
I can’t find anything significant about the grid to plate lead proximity, at least not for one stage in isolation, and the snubber caps on those stages are huge compared to the plate to cathode lead capacitance... two orders of magnitude larger.
Interesting. It definitely made a difference for me (maybe confirmation bias). Charlie W can lend his bat-ears next week and prove me bonkers
I'd love to know why Mr. Dumble looked to be pretty particular about this part of his lead dress.
Running wires down on the chassis will introduce capacitance of about 1pF per inch to ground, which will only affect extremely high frequencies. I would expect similar results running plate and cathode wires close together on the chassis for a couple of inches, which will put a couple of pF between them, and also to ground on each. I can see that in a simulation, it's a loss of about 0.1 dB at 20kHz, but that's going to be too small to see on the scope.
Thanks Martin I was aware that added some capacitance but not aware of how much per inch.
Ian
This has been discussed here quite a bit throughout the years Some people here who have claimed to have heard it makes a difference,others who have said they don't really hear much there. https://ampgarage.com/forum/viewtopic.p ... 663#p27663
This is not sayin anyone is right or wrong and Martin is the 1st here to actually measure it out on the bench which is always a big help I am a big believer in getting another set of good ears involved with these kinds of things and Charlie's got em!!
Looking forward to your findings
Tony
" The psychics on my bench is the same as Dumble'"
To Lauri's point an ultrasonic oscillation would certainly cause problems, and I suspect that is what people are hearing. You need positive feedback for that, though, and of course plate and grid are out of phase. I can drive this breadboard stage at 100 kHz with sine and square wave signal, and see the gain roll off as expected, but no hint of oscillation. This type of breadboard has lots of stray capacitance, but I've tried to keep things well separated except for the grid and plate leads running parallel. It is only the one stage, though, so there is no opposite phase signal on the other triode.
In the V2 area there are a couple of things that should help to curb oscillations, namely the large grid stoppers mounted close to the socket pins, and the snubber caps. I have seen people position the snubbers close together, though, and I recall one case where that was found to be causing an oscillation.
Interesting topic for sure! I built my OTS as a kit from Ceriatone. It's the FM50 ME mod. And I basically followed the lead dress of the Flckr photos that are posted for helping those of us during the build.
This is my V2 lead dress, how does it look? Should I make any changes with the plate/grid lay? I do feel that my OD needs low end 'tightness' addressing.
I know for a 1000% fact that if your plate and grid wires are physically touching, the amp will absolutely not function correctly. Just try it. Push the V2a grid onto the plate. Touching. Then play the amp loudly. Even the bass control stops working correctly. Terrible abrasive sound. I just last week spent hours troubleshooting a high end clone and the grid and plate wires were touching on V2a. I separated them and the amp kills now. I tried changing the bass cap, the bass pot, the .001 on the bass pot. The control was almost cutting the bass in and out as you turned it! The wires were the cause. No breadboard needed.
Try touching the grid wire. You will hear microphonic noise. Now, imagine the amp vibrations of the grid and plate rubbing, Not open for discussion. It kills the amp sound. Not just a little. I can’t believe we are arguing whether the grid and plate wires actually touching is OK.
A number of years ago I fixed a ceriatone for a friend. The amp had no sustain and the volume was pumping in and out. Turns out Nick bent the V1a grid resistor down and the body was contacting the plate. I bent the resistor back up and voila. Sustain and fatness returned. No pumping in and out.
One other easily noticeable thing. Try pushing the cl2 .05 coupler towards the .002 treble midboost cap. Play. Then move it away. The amp is fatter with some space between them. Always keep out of phase stages away from one another. Ken Fisher would roll in his grave that there are three pages of this…
Who needs a breadboard when you can just do the test on the real amp. It is not subtle. It is a huge and extremely noticeable difference.
martin manning wrote: ↑Sun May 09, 2021 1:50 am
I can’t find anything significant about the grid to plate lead proximity, at least not for one stage in isolation, and the snubber caps on those stages are huge compared to the plate to cathode lead capacitance... two orders of magnitude larger.
Interesting. It definitely made a difference for me (maybe confirmation bias). Charlie W can lend his bat-ears next week and prove me bonkers
I'd love to know why Mr. Dumble looked to be pretty particular about this part of his lead dress.
Running wires down on the chassis will introduce capacitance of about 1pF per inch to ground, which will only affect extremely high frequencies. I would expect similar results running plate and cathode wires close together on the chassis for a couple of inches, which will put a couple of pF between them, and also to ground on each. I can see that in a simulation, it's a loss of about 0.1 dB at 20kHz, but that's going to be too small to see on the scope.
Thanks Martin I was aware that added some capacitance but not aware of how much per inch.
Ian
This has been discussed here quite a bit throughout the years Some people here who have claimed to have heard it makes a difference,others who have said they don't really hear much there. https://ampgarage.com/forum/viewtopic.p ... 663#p27663
This is not sayin anyone is right or wrong and Martin is the 1st here to actually measure it out on the bench which is always a big help I am a big believer in getting another set of good ears involved with these kinds of things and Charlie's got em!!
Looking forward to your findings
Yes. Separate the snubbers. They are out of phase. There should be a gap between them.
daniboy79 wrote: ↑Sun May 09, 2021 1:01 pm
Interesting topic for sure! I built my OTS as a kit from Ceriatone. It's the FM50 ME mod. And I basically followed the lead dress of the Flckr photos that are posted for helping those of us during the build.
This is my V2 lead dress, how does it look? Should I make any changes with the plate/grid lay? I do feel that my OD needs low end 'tightness' addressing.
daniboy79 wrote: ↑Sun May 09, 2021 1:01 pm
Interesting topic for sure! I built my OTS as a kit from Ceriatone. It's the FM50 ME mod. And I basically followed the lead dress of the Flckr photos that are posted for helping those of us during the build.
This is my V2 lead dress, how does it look? Should I make any changes with the plate/grid lay? I do feel that my OD needs low end 'tightness' addressing.
Try it, it can't hurt
Looks like your OD trigger is on an external mounted pot with shielded cable so that can't be changed. I would take a look at the pics of examples (#124 and #133 come to mind) and try and emulate the plate and cathode lead dress. Will be a great experiment to see if moving them makes a difference for you.
Here is a Dumble I was in. There is a noticeable gap between all plates and grids. I think that people see pics from certain angles and can’t tell that and intentionally dress the stage to look like the Dumble pic. Folks like Nick at Ceriatone. Hence the repair I did on the amp with V1a grid and plate touching. Just horrid unplayable amp.
Every single a Dumble I have either been in, or seen pics, absolutely has space between the pates and grids. Period.
Full shot of the first amp. A Bluesmaster. Kind of meh, but still a Dumble. Did not compare to Larry’s or Robben’s, both of which I have played. Robben’s was far better than Larry’s in case anyone is wondering.
Not touching. Even 1mm fixes it. They can’t touch. The vibrations kill things.
martin manning wrote: ↑Sun May 09, 2021 1:46 pm
I don't know dog, in both of those photos both the V1a grid lead and grid resistor look pretty close to the plate lead to me.
Audiodog wrote: ↑Sun May 09, 2021 1:48 pm
Not touching. Even 1mm fixes it. They can’t touch. The vibrations kill things.
martin manning wrote: ↑Sun May 09, 2021 1:46 pm
I don't know dog, in both of those photos both the V1a grid lead and grid resistor look pretty close to the plate lead to me.
Then why do you suppose I can bang them together on the breadboard stage and see nothing?
No clue. I spent hours with a clone last week, pulling my hair out. The bass control pumped in and out as you moved it while playing. Amp sounded so bad that the owner shipped it 3000 miles to me to work on. He has had it ten years and never plays it because it was not good.
The issue was entirely the V2a plate and grids touching. I separated them and the control now works right and the amp is fatter and without the edgy bad distortion it had.
Audiodog wrote: ↑Sun May 09, 2021 1:48 pm
Not touching. Even 1mm fixes it. They can’t touch. The vibrations kill things.
martin manning wrote: ↑Sun May 09, 2021 1:46 pm
I don't know dog, in both of those photos both the V1a grid lead and grid resistor look pretty close to the plate lead to me.
Then why do you suppose I can bang them together on the breadboard stage and see nothing?
Audiodog wrote: ↑Sun May 09, 2021 1:48 pm
Not touching. Even 1mm fixes it. They can’t touch. The vibrations kill things.
martin manning wrote: ↑Sun May 09, 2021 1:46 pm
I don't know dog, in both of those photos both the V1a grid lead and grid resistor look pretty close to the plate lead to me.
Then why do you suppose I can bang them together on the breadboard stage and see nothing?
I think a single tube experiment and a full-blown amp with a power section have a slightly different vibration profile
I can definitely hear a difference and obviously Mr. D was very intentional about separating those leads so it may be something you want to try before buttoning up your amp and calling it done.
