Lt Bob amp build - an alliance of superpowers

[JD01]

Its a thing of beauty.

[Tadpui]

Hell yeah, looks awesome guys!

[Greg_L]

Thanks dudes!


[mention]Lt. Bob[/mention] now that I'm back I'm gonna try to break your amp now, mmmkay? I'm gonna work it hard. If it passes my tests it'll be ready to ship.

[Lt. Bob]

Thanks dudes!


Lt. Bob now that I'm back I'm gonna try to break your amp now, mmmkay? I'm gonna work it hard. If it passes my tests it'll be ready to ship.

sounds good ....... blow it up if you can!


don't forget to sign it.

Also I'm curious ...... do you have an opinion on the orange drops yet?

[Greg_L]

sounds good ....... blow it up if you can!


don't forget to sign it.

Also I'm curious ...... do you have an opinion on the orange drops yet?

Not really yet. My very first impression is that right off the bat yours sounded better than mine when mine was new. But I had issues to fix with mine where yours seems good to go right out of the gate. Mine got sweeter as it broke in, yours seems sweet right off the bat, and maybe might get even better. But that's speculation right now. I got to use my own experience with my own amp in building yours, and I truly think yours came out better so far. I can't chalk that up to orange drops though. I think I built yours overall better in general.

[Greg_L]

To add to that....I think I'll be gutting mine later and redoing some things. I wired mine in a way that made sense at the time, and it works well, but now I see it was too complicated and unnecessary. I wanted to be able to flip the board on mine and now I know I don't need to. So I think I'll be removing my board and wiring it up more sensibly...and probably going back in with orange drops too. I don't have to remove the board to replace the current caps with orange drops, but I might as well put them in if I'm yanking the board. Or maybe I'll go full fancy with some Sozos or Mallorys. I'm not a believer in caps being big tone makers, but maybe they do if it turns out Boob's orange drops make a difference.

But before I do that, we gonna do an 18w Marshall and I've got my own Blonde-era Bassman to build.

[Lt. Bob]

well, you have some spare orange drops ..... may as well use 'em

[Greg_L]

well, you have some spare orange drops ..... may as well use 'em

Yeah I was gonna send them back with your amp but maybe see if I could buy them off of you since they're already here.

[Lt. Bob]

you can have them ...... it's not like they're gold ,..... just keep ;em. One less thing for me to find a place for.

Oh, and obviously I have 'net gain ...... still no power.
But I have my trusty generator going ...... have to take a shower.
We have an electric water heater ...... so that means .... duh duh duh .... a cold shower!

[Greg_L]

you can have them ...... it's not like they're gold ,..... just keep ;em. One less thing for me to find a place for.

Oh, and obviously I have 'net gain ...... still no power.
But I have my trusty generator going ...... have to take a shower.
We have an electric water heater ...... so that means .... duh duh duh .... a cold shower!

Ok cool thanks!

I don't suspect a cold shower is that bad a thing during Florida summer. I know here in Texass I haven't used hot water in months.

[Greg_L]

Update:

I still have [mention]Lt. Bob[/mention]'s amp.

It was all done and buttoned up...then I noticed a tiny problem. There is a little tiny smidgen of guitar signal getting through to the speaker with the channel volumes turned all the way down. Same issue on both channels. Turn the volume off, bang a chord or a note, and you can faintly hear it through the speaker. This truly is not an actual problem, the amp works perfectly and sounds amazing. But I don't wanna let this out the door so I tore back into it. I noticed that the volume pots themselves were really stiff and hard to turn compared to the rest of the pots so I thought well that has to be it. We got new pots, didn't fix it. But at least they spin nicely now. So I poked and prodded and moved things around and checked and re-checked grounds and looked literally everywhere for why this thing is leaking signal. Everything was perfect. I got a new scope and probed every connection in this thing. I found where the "leak" is happening. Same spot on both channels. The first stage in each channel is leaking into the second stage without taking it's proper route. It's basically bypassing the volume pot and going straight into the second half of each preamp tube. But how? With the assistance of some hardcore amp gurus I know they had me doing all kinds of tests. I narrowed it down to bad tube sockets or a conductive board. The verdict - it's a conductive board. Probing the eyelet board in that area shows signal on the scope. Obviously a piece of stiff cardboard is not part of the circuit, but it's passing a tiny bit of signal. The two terminals that connect to the two plates of each preamp tube are close together on the board and a little taste of the signal is bridging the gap through the air or through the board. It's the board. Without replacing the entire board or re-wiring that section with turret strips there isn't anything we can do about it. It just is what it is. It doesn't affect the performance of the amp. It's just a weird little bug.

The gurus I consulted with during this ordeal all laughed at me the whole time. Their general attitudes went in two similar directions....
1) Who cares? No one plays an amp with the volumes on zero. Greg stop being a little bitch and just play the damn thing.
2) It just is what it is. This happens all the time on lots of amps and it's no big deal. I know it's pretty common with any Fender amp that has the classic black fiberboard. But I want it to be perfect.

So we have to just accept it. And I'm fine with that finally knowing that it's not actually something I did wrong. I did learn a fucking lot about signal tracing and troubleshooting though. Frustrating, but this will be very useful experience in the future. And I will never use Fender-style eyelet boards again.

ANYWAY......tone clips here

[WhiskeyJack]

That settles it. I don't think i will ever try to DIY an amp after your last bunch of builds. MAybe a little 1 watter or something. Maybe, but this post alone is enough reason for me to focus on other things.

The verdict - it's a conductive board. Probing the eyelet board in that area shows signal on the scope. Obviously a piece of stiff cardboard is not part of the circuit, but it's passing a tiny bit of signal. The two terminals that connect to the two plates of each preamp tube are close together on the board and a little taste of the signal is bridging the gap through the air or through the board. It's the board. Without replacing the entire board or re-wiring that section with turret strips there isn't anything we can do about it.

Isn't there like an electrical sealing kind of gunk you could put around those two eyelets? Like some sort of caulking or something that could gob on there? or inbetween the two? Like a faux insulator kind of thing? Layers of electrical tape.

Not pretty. But might hinder it a bit? Unless the bridge is going through the cardboard in which case, boourns to that.

[Greg_L]

Isn't there like an electrical sealing kind of gunk you could put around those two eyelets? Like some sort of caulking or something that could gob on there? or inbetween the two? Like a faux insulator kind of thing? Layers of electrical tape.

Not pretty. But might hinder it a bit? Unless the bridge is going through the cardboard in which case, boourns to that.

It's getting through the board. Anything we can do to the exterior of the board doesn't stop it from traveling through the middle. Also, this could happen with a one watt, 50 watt, any watt amp. This issue is happening in the preamp. A one watt preamp isn't much, if any, different from any other preamp. The preamp doesn't care how much power the output section makes. It just does what it does. The problem here is that the leakage is happening in the preamp and there's nothing to stop it from traveling on down to the phase inverter. From there it's on to the power tubes. From there, the speaker.

I'm gonna explain this very generally. It's sort of long but I think it might make sense if you want to get an inkling of how this works. Grab a beer....

There are three main parts to a typical guitar amp preamp tube. Plate, grid, and cathode. This is why they're called a "triode" tube. 12AX7s are a dual triode - two triodes in one tube. The plates (anode) of a tube are the positive charge. The cathodes are the negative charge. Electrons are heated on the cathode by the heater filament winding and they are very excited to leave. Electrons want to flow from the cathode to the plate. They can't wait to get the fuck off that cathode. The grid sits between the cathode and the plate and it controls the flow of electrons. When we play a note our guitar signal hits the grid, which is sort of like a wall, and it lets the electrons flow through. Think of a cartoon when a character runs through a wall and the hole in the wall is the exact shape of the character that just ran through it. Our guitar signal is making a hole in the grid's wall. The negatively charged electrons on the cathode very badly want to get to the positively charged plate, so they rush through the hole in the grid and slam themselves into the plate in the exact shape of the hole made by our guitar signal. We start the process with our tiny little weak guitar signal, and the result is a much larger version of that same shape. This violent process of hyperactive heated electrons rushing to the plate in the exact shape of our guitar signal is amplification. The difference in voltage between cathode and plate gets those electrons screaming through the grid, and those electrons leave the tube through the plate. This is the AC guitar signal part of it.

The plate obviously needs positive voltage to be so ready and willing to accept this blast of feisty electrons. And that voltage has to be DC. Nice smooth steady unwavering DC voltage. We power up the plate with positive DC voltage, a lot of it, and at the same time we have our amplified AC signal traveling through the same wire the other way. DC is charging the plate and AC is coming out of it. AC and DC can live in the same wire at the same time.

Okay so with all that sub-atomic electrical shit going on at light speed, remember that we have two triodes working in the same tube. The first stage and the second stage. You might have seen tube-talk nomenclature like V1a or V1b. That simply means V1 - the first preamp tube, and the a or b signifies the first or second half of the tube. The first stage grid is linked directly to the input jacks. Remember the grid? It is the wall that our guitar signal punches a hole into. In this particular amp the guitar is tied directly to the grid of the first half of the first tube. Direct shot. This first stage of amplification happens regardless of anything else in the amp. It is independent of every volume or tone control. It is before everything. If the amp is on and off standby, that first stage just happens. Whether you hear it or not is dependent on other things, but that very first stage of amplification is happening.

So what we have going on here is that the first stage is amplifying the guitar signal like it's supposed to. No problem there. Then that signal goes down to the volume pot and the vol pot controls how much of that amplified signal passes along to the rest of the amp. The volume pot is the ultimate gatekeeper between the first and second stage of the tube. But the way the eyelet board is designed, it has the tube's two plate wire connections very close to each other. So we have two wires with equal DC voltage between them, but a huge AC differential. The first stage wire is carrying current, the second stage isn't. The potential between the two plate wire connection points and the sheer force of all that DC voltage is letting a little bit of the first stage's amplified signal transfer into the second stage plate wire independent of the volume pot or any second stage grid control. And since both channels of the amp are laid out in the exact same way, it's happening on both channels. This electrical short-cutting always wants to happen in any amp, but it usually can't because there's no direct connection between the two plate wires. But in this case, there is an accidental inadvertent path for signal leakage - the close proximity of plate wire connections and a fucking conductive eyelet board.

[Lt. Bob]

gatekeepers can be sloppy ..... it's like the guy holding the velvet rope at that club that won't let you in but the pretty girls slip right by

[Greg_L]

gatekeepers can be sloppy ..... it's like the guy holding the velvet rope at that club that won't let you in but the pretty girls slip right by

Yeah except this gatekeeper is doing it's job. Your amp situation is more like the guys in the kitchen letting a few people in through the back door so they don't even have to mess with the velvet rope.

[Lt. Bob]

well, however my amp is working is how all amps should work because mine is the best!

[Greg_L]

well, however my amp is working is how all amps should work because mine is the best!

Like you said in the email...tons of amps probably do this and we never even notice it. Two of my Marshalls do it, and through dissecting yours I discovered my own Fender build does it and I'd never even noticed it before.

[WhiskeyJack]

Isn't there like an electrical sealing kind of gunk you could put around those two eyelets? Like some sort of caulking or something that could gob on there? or inbetween the two? Like a faux insulator kind of thing? Layers of electrical tape.

Not pretty. But might hinder it a bit? Unless the bridge is going through the cardboard in which case, boourns to that.

It's getting through the board. Anything we can do to the exterior of the board doesn't stop it from traveling through the middle. Also, this could happen with a one watt, 50 watt, any watt amp. This issue is happening in the preamp. A one watt preamp isn't much, if any, different from any other preamp. The preamp doesn't care how much power the output section makes. It just does what it does. The problem here is that the leakage is happening in the preamp and there's nothing to stop it from traveling on down to the phase inverter. From there it's on to the power tubes. From there, the speaker.

I'm gonna explain this very generally. It's sort of long but I think it might make sense if you want to get an inkling of how this works. Grab a beer....

There are three main parts to a typical guitar amp preamp tube. Plate, grid, and cathode. This is why they're called a "triode" tube. 12AX7s are a dual triode - two triodes in one tube. The plates (anode) of a tube are the positive charge. The cathodes are the negative charge. Electrons are heated on the cathode by the heater filament winding and they are very excited to leave. Electrons want to flow from the cathode to the plate. They can't wait to get the fuck off that cathode. The grid sits between the cathode and the plate and it controls the flow of electrons. When we play a note our guitar signal hits the grid, which is sort of like a wall, and it lets the electrons flow through. Think of a cartoon when a character runs through a wall and the hole in the wall is the exact shape of the character that just ran through it. Our guitar signal is making a hole in the grid's wall. The negatively charged electrons on the cathode very badly want to get to the positively charged plate, so they rush through the hole in the grid and slam themselves into the plate in the exact shape of the hole made by our guitar signal. We start the process with our tiny little weak guitar signal, and the result is a much larger version of that same shape. This violent process of hyperactive heated electrons rushing to the plate in the exact shape of our guitar signal is amplification. The difference in voltage between cathode and plate gets those electrons screaming through the grid, and those electrons leave the tube through the plate. This is the AC guitar signal part of it.

The plate obviously needs positive voltage to be so ready and willing to accept this blast of feisty electrons. And that voltage has to be DC. Nice smooth steady unwavering DC voltage. We power up the plate with positive DC voltage, a lot of it, and at the same time we have our amplified AC signal traveling through the same wire the other way. DC is charging the plate and AC is coming out of it. AC and DC can live in the same wire at the same time.

Okay so with all that sub-atomic electrical shit going on at light speed, remember that we have two triodes working in the same tube. The first stage and the second stage. You might have seen tube-talk nomenclature like V1a or V1b. That simply means V1 - the first preamp tube, and the a or b signifies the first or second half of the tube. The first stage grid is linked directly to the input jacks. Remember the grid? It is the wall that our guitar signal punches a hole into. In this particular amp the guitar is tied directly to the grid of the first half of the first tube. Direct shot. This first stage of amplification happens regardless of anything else in the amp. It is independent of every volume or tone control. It is before everything. If the amp is on and off standby, that first stage just happens. Whether you hear it or not is dependent on other things, but that very first stage of amplification is happening.

So what we have going on here is that the first stage is amplifying the guitar signal like it's supposed to. No problem there. Then that signal goes down to the volume pot and the vol pot controls how much of that amplified signal passes along to the rest of the amp. The volume pot is the ultimate gatekeeper between the first and second stage of the tube. But the way the eyelet board is designed, it has the tube's two plate wire connections very close to each other. So we have two wires with equal DC voltage between them, but a huge AC differential. The first stage wire is carrying current, the second stage isn't. The potential between the two plate wire connection points and the sheer force of all that DC voltage is letting a little bit of the first stage's amplified signal transfer into the second stage plate wire independent of the volume pot or any second stage grid control. And since both channels of the amp are laid out in the exact same way, it's happening on both channels. This electrical short-cutting always wants to happen in any amp, but it usually can't because there's no direct connection between the two plate wires. But in this case, there is an accidental inadvertent path for signal leakage - the close proximity of plate wire connections and a fucking conductive eyelet board.

Man this is more thna i have ever wanted to know dude. thanks for taking the time to explain it to us. I am glad it is here and i feel like this thread should really get stickied but i say that about all the threads in this particular part of the forum.

[Lt. Bob]

well, however my amp is working is how all amps should work because mine is the best!

Like you said in the email...tons of amps probably do this and we never even notice it. Two of my Marshalls do it, and through dissecting yours I discovered my own Fender build does it and I'd never even noticed it before.

lol ...... 2 of your Marshalls do it?

I'ma start checking every amp for this now!

[Greg_L]

lol ...... 2 of your Marshalls do it?

I'ma start checking every amp for this now!

Yup, my oldest Marshalls do it. I think in my scenario it's just very old pots that might just need a good cleaning. But as I know now that could be wrong. I haven't investigated it because I don't really care. I don't want it to happen, but it doesn't affect anything. Like the gurus said, why would I care what it does on zero when it's usually on 10?