Weber 6O100 Build Issues

[csjoyner]

Yes. The black wire on the first and the white wire on the fourth are the filter choke.

There is a wire under the board connecting the top two smaller caps and the top of the cap in the bias circuit so all of those are grounded. (See pic) They are grounded with the larger caps to the actual ground wire and not to the back of the pots. We originally had them grounded to the back of the pots but changed them to see if it made a difference. It did not.

[csjoyner]

While posting that last pic I realized that the one vertical wire is a signal wire while the two that cross it are b+ power wires (C and D). Two questions:

Could that be the issue?

If so, which wire(s) should I run on top, the two power wires or the signal wire?

[TUBEDUDE]

It's easier to move one than two, but that's likely not your problem. They cross roughly perpendicular, minimizing any coupling. The level of coupling is dependent on the cleanliness of your B+ on the lines and the relative level of your signal line. What impedance? Is it a low level or higher level signal line? A preamp grid connection or a plate output signal?

[csjoyner]

It’s a grid wire. It connects directly to pin 7 on V2.

I’m not sure which impedance you are referring to. What are you looking for and how do I check it. We have this problem in all selections of speaker impedance: 4,8,and 16.

[TUBEDUDE]

Sorry, I was too technical. All points of a circuit have an impedance. They are much higher than the output to your speakers. Your guitar pickups have an impedance of several thousand Ohms. The impedance of a point in the circuit will vary. At any point, all things being equal, the higher the impedance, the greater susceptibility to noise.
A preamp tube will have a plate impedance of tens of thousands of Ohms, the grid, will have ten or a hundred times that, making it more sensitive and susceptible to pickup errant noise or signal. In short, as signal at the grid is usually amplified many fold, any noise coupled to a grid wire will be more prominent than the same noise coupled to a plate wire.
I know I'm explaining this badly. Please see the thread "Reading material on steroids", and some texts on electronics. Merlin's book on Designing Tube Preamps, is a good start.

[csjoyner]

Sorry, I was too technical. All points of a circuit have an impedance. They are much higher than the output to your speakers. Your guitar pickups have an impedance of several thousand Ohms. The impedance of a point in the circuit will vary. At any point, all things being equal, the higher the impedance, the greater susceptibility to noise.
A preamp tube will have a plate impedance of tens of thousands of Ohms, the grid, will have ten or a hundred times that, making it more sensitive and susceptible to pickup errant noise or signal. In short, as signal at the grid is usually amplified many fold, any noise coupled to a grid wire will be more prominent than the same noise coupled to a plate wire.
I know I'm explaining this badly. Please see the thread "Reading material on steroids", and some texts on electronics. Merlin's book on Designing Tube Preamps, is a good start.

Do I measure the resistance from the connection to ground?

[TUBEDUDE]

It's not that simple I'm afraid. Impedance is combined resistance, capacitive reactance and inductive reactance. Practically you don't need to measure it. You will learn what parts of the circuit will have either a high, medium or low Impedance, and know there relative sensitivity. This can aid you in designing and troubleshooting. To start know generally grid circuits are high and plate circuits are lower.
Sorry to derail w/ a tangent everyone.

[TUBEDUDE]

Back to the issue. With what you've checked, and followed advice upthread, much is eliminated. The main clue is the doubled tubes. I assume you've used all socket options with two tubes. That rules out the sockets. So that leaves the output tyranny, not very likely, a connection or component that gets flaky with the additional current, or a non- circuit path coupling made possible with the increase in current or signal. I'm betting on number two.

[csjoyner]

Back to the issue. With what you've checked, and followed advice upthread, much is eliminated. The main clue is the doubled tubes. I assume you've used all socket options with two tubes. That rules out the sockets. So that leaves the output tyranny, not very likely, a connection or component that gets flaky with the additional current, or a non- circuit path coupling made possible with the increase in current or signal. I'm betting on number two.

So what do we try next? We used shielded wire on all the sensitive wires. Should we move the signal wire in the back to the top? Is it ok to do that. The guys from Weber said not to run signal wires on top of the board but I can’t help thinking that’s better than running 2 power wires the distance of the board on top.

[TUBEDUDE]

If you think that's it, you could rewire that line so it exits the turret perpendicular to the board, straight to the chassis. Then run it along the chassis floor to the far connection.
I've never had to use shielded cable on low gain amplifiers before. You've touched up all your solder connections, right?

[pdf64]

There’s a feedback loop, which incorporates the presence control. Does the setting of that affect the issue?

[csjoyner]

There’s a feedback loop, which incorporates the presence control. Does the setting of that affect the issue?

YES!!! If it’s turned all the way down the popping is worse. What do we do about it?

[pompeiisneaks]

Could be the phase of the NFB is reversed, you can try to disconnect it temporarily and if the issue is gone, then it's the NFB that causes it. You can then restore it and attempt swapping the OT leads to the power tubes, or swap the PI outputs to the Power tube grids and see if it's resolved.

Normally this presents as howling, but sometimes it can be more subtle with weird issues like you're seeing.

OR It could be that the NFB presence cap has something wrong with it and is leaking dc?

Not sure of other issues that may be present causing this.

~Phil

[csjoyner]

Could be the phase of the NFB is reversed, you can try to disconnect it temporarily and if the issue is gone, then it's the NFB that causes it. You can then restore it and attempt swapping the OT leads to the power tubes, or swap the PI outputs to the Power tube grids and see if it's resolved.

Normally this presents as howling, but sometimes it can be more subtle with weird issues like you're seeing.

OR It could be that the NFB presence cap has something wrong with it and is leaking dc?

Not sure of other issues that may be present causing this.

~Phil

Just to make sure I have this right.

Disconnect the NFB. Is that the wire that connects to the yellow wire of the OT on the impedance selector?

If that fixes problem, then reconnect wire and switch the PI to the power tubes. Should I do this at the master volume pot or is there a better place to do this? Or am I just wrong on that one. We have already tried switching the OT wires to the power tube with no change.

We will check the cap at the NFB too.

[pompeiisneaks]

Yes it's the wire that comes off of one of the output jacks to the main circuit. Disconnect it anywhere carefully set aside.

If the noise is gone it's in the NFB, so either the OT phase on the power tubes is backwards so swap the ot primaries or swap the PI output to the tubes.

~Phil