I said to switch to 12AT7 for a reason. Try it out and see what happens. If not better, raise the plate voltages.
NFB is kinda bad for the distortion we prefer, but it's good for some issues.
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I said to switch to 12AT7 for a reason. Try it out and see what happens. If not better, raise the plate voltages.
Ok here is with the PI 12at7I said to switch to 12AT7 for a reason. Try it out and see what happens. If not better, raise the plate voltages.
NFB is kinda bad for the distortion we prefer, but it's good for some issues.
There is already 100pf theregeoff 1965 wrote: ↑Sat 01/09/21 7:41 amhave you tried a 47 or 100pf snubber across the phase plates?
Set up the PI so the voltages are on target to what I sent you with the 12AT7. You will need to lower your tail resistor, try 22K. This won't likely fix the problem, but it will be setup well for when the problem is resolved.
I have news. I put the signal from point x into the poweramp of the modern classic. Guess what? Fizz.JMPGuitars wrote: ↑Sat 01/09/21 8:52 amSet up the PI so the voltages are on target to what I sent you with the 12AT7. You will need to lower your tail resistor, try 22K. This won't likely fix the problem, but it will be setup well for when the problem is resolved.
Considering everything we've tried, it's likely the fault lies within the tubes or the OT. Either way, you should still try the snubber circuit. At this point I'm leaning towards a defective OT.
Thanks,
Josh
Are the preamp tubes new? Post some photos of your build.
Personally.. with these values now it's no more fizzy than my modern classic. It's also much more gainy. I'm going to try the CR on V1 like you proposed. Put 22k on the PI plates? Should I up the cathode resistors to lower the cathode voltages? Like 470K perhaps?JMPGuitars wrote: ↑Sat 01/09/21 9:24 amAre the preamp tubes new? Post some photos of your build.
Try adding a bypass cap to R3. .68µF to 2.2µF. You can also try increasing that resistor value to between 1.5K and 2.2K.
Did the changes.. but I can't test on volume because my daughter is asleep..JMPGuitars wrote: ↑Sat 01/09/21 10:32 am
No, 22K TAIL resistor. 470 ohm (not K) cathode resistor.
PI change:
PI-Tail.jpg
Preamp change:
V1-Input.jpg
Don't make any more changes until you listen to it at volume.
Played it. Sounds pretty fine that way. Fizz, but yeah...JMPGuitars wrote: ↑Sat 01/09/21 5:37 pmDon't make any more changes until you listen to it at volume.
Awesome. I'm thinking that getting the snubber circuit in there may help with the remaining carbonation. Certainly worth a shot.
Yeah, but I need some parts... have all but the 8M2 resistors.. + I used the 1k5 5W resistors for the screens.JMPGuitars wrote: ↑Sun 01/10/21 8:30 amAwesome. I'm thinking that getting the snubber circuit in there may help with the remaining carbonation. Certainly worth a shot.
That's not meaningful. One of them was done that way to not pass through the grid line (schematic clarity), and the other makes no sense not to just draw a line there, pretty weird, but still all of them mean the same thing. Good ground schemes are good ground schemes, if you followed what you know from the other builds, you should be fine.Bieworm wrote: ↑Tue 01/12/21 11:20 amJosh.. if you look closely at the schematic it appears some pots have a different mark for grounding point. Is the series grounding of pots with 1 wire to ground near the input likely to cause oscillation? It looks to me like all preamp components and the midbite pot should be grounded on the ground buss?
Did the snubber yesterday. It only darkened the tone. I put the 1000pf back in because it didn't solve anything.JMPGuitars wrote: ↑Tue 01/12/21 12:06 pmThat's not meaningful. One of them was done that way to not pass through the grid line (schematic clarity), and the other makes no sense not to just draw a line there, pretty weird, but still all of them mean the same thing. Good ground schemes are good ground schemes, if you followed what you know from the other builds, you should be fine.Bieworm wrote: ↑Tue 01/12/21 11:20 amJosh.. if you look closely at the schematic it appears some pots have a different mark for grounding point. Is the series grounding of pots with 1 wire to ground near the input likely to cause oscillation? It looks to me like all preamp components and the midbite pot should be grounded on the ground buss?
Either way, not likely to cause an oscillation, and also not likely that you actually have an oscillation. You've got a gremlin.
From this question I assume you're still having an issue. I think you should be patient until you get the snubber parts you need. Besides that, you could try leaving the 12AT7 in the PI, and try a lower gain tube in V1. 12AT7 would be a good starting point if you have another.