Weber 6O100 Build Issues

[csjoyner]

My brother and I are having issues with our Weber 6O100 build. When turning the volume up past 3 it makes this horrible loud popping noise. It does it when playing guitar through the amp. It is a steady machine gun sound. At around 5 we also get a squeal with it. We have tried numerous suggestions from Weber but none of them made any difference. We have included pics. Everything is correct according to the layout. We made our own board as the one provided was not big enough to fit the components. We used shielded wire at a few points and the ground wires on the B+ power is separate from the audio grounds. It makes the same sound with another set of tubes so it is not them. We do not get the popping when running the amp at 50 watts (2 tubes instead of 4). We tried switching the wires from the output transformer but nothing. We are looking for any suggestions as we are at a loss. Thanks.

[jajoyner]

here is a sample of what we are hearing when strumming the guitar with the volume above 3.

[Phil_S]

I think that is called "motor boating."
No, that's not it.
<edit; snipped content that was wrong; I'm embarrassed, but I don't need to leave it here>

[martin manning]

Motorboating is a steady thumping at a few Hz. Are you cutting the load in half when to run it with four tubes? It sounds like arcing somewhere.Turn the lights out and see if you can see any in or around the power tubes.

[pompeiisneaks]

Sounds an awful lot to me like arcing of something. Either a tube or some component is making intermittent contact due to poor solder connection etc.

I'd try turning off all the lights and look for any bright flashes in the tubes or on the board etc.

~Phil

[jajoyner]

Hi kids! Thanks for the input. We are going to check on this over the weekend. We will let you know what we find.

[jajoyner]

Are you cutting the load in half when to run it with four tubes?

Not sure what you mean by this. What we did was cut the power down by removing 2 of the tubes. This resolved the issue. We did this to swap out and test all tubes and all sockets. We got this idea from the link below:
https://www.premierguitar.com/articles/ ... duce-power

It is not a constant sound. Only happens when strumming the guitar.

We turned out the lights and saw no sparking at all. Could it be arcing and it's just not visible?

[pompeiisneaks]

It could be inside of a component... or underneath a board somewhere?

~Phil

[martin manning]

Are you cutting the load in half when to run it with four tubes?

Not sure what you mean by this. What we did was cut the power down by removing 2 of the tubes. This resolved the issue. We did this to swap out and test all tubes and all sockets. We got this idea from the link below:
https://www.premierguitar.com/articles/ ... duce-power

It is not a constant sound. Only happens when strumming the guitar.

We turned out the lights and saw no sparking at all. Could it be arcing and it's just not visible?

Refer to that article where it says you need to move the impedance selector down one click when you remove two of four tubes. Do you have it set correctly in each case? There could be arcing across the power tube socket lugs inside the chassis, and once that has occurred tracks of carbonized material are created which make it much more likely that it will occur again.

[sluckey]

The premierguitar article says this about that...

After removing the two output tubes, there’s another step that is theoretically necessary, and you should take it if possible. This is to change the output impedance selection to reduce the speaker load by half. For example, if you are running your amp into a 16 ? load, reduce the impedance selector to 8 ?. For an 8 ? load, reduce the impedance selector to 4 ?.

But that is ass backwards. When you pull two of the tubes the primary impedance doubles, so the speaker impedance must also double to maintain the proper impedance ratio. In the case of the TR example which has a 4Ω speaker load, when you pull two tubes you should also disconnect one speaker which doubles the speaker load to 8Ω.

[pdf64]

It could be parasitic oscillation, rather than arcing.
I’ve had a TR in for repair that did similar, signal accompanied with blipping. Ended up being a bad 0V to chassis connection.
I guess there’s a global nfb loop around the power amp; how about if the amp is operated open loop?
Schematic?

[martin manning]

The premierguitar article says this about that...

After removing the two output tubes, there’s another step that is theoretically necessary, and you should take it if possible. This is to change the output impedance selection to reduce the speaker load by half. For example, if you are running your amp into a 16 ? load, reduce the impedance selector to 8 ?. For an 8 ? load, reduce the impedance selector to 4 ?.

But that is ass backwards. When you pull two of the tubes the primary impedance doubles, so the speaker impedance must also double to maintain the proper impedance ratio. In the case of the TR example which has a 4Ω speaker load, when you pull two tubes you should also disconnect one speaker which doubles the speaker load to 8Ω.

I'd say half-ass backwards. You double the speaker load when you pull half the tubes, so that part is wrong. But, you can do that by literally doubling the speaker load (disconnect one speaker if they are wired in parallel, or use a different cab), or by miss-matching the impedance selector down one click. That option is correctly described in the example. If the author had said "This is to change the output impedance selection to reduce the expected speaker load by half," he would have been correct.

[Phil_S]

I wonder if it's as simple as a bad tube. After pulling two tubes, did you swap the pulled pair for the pair you left installed? If the sound returns, then you know. It's a cheap and quick diagnostic.

[csjoyner]

We saw nothing from underneath the boards. Which component would be arching and how would we know? We have tested all with a multimeter and each one passed.

When we pulled 2 tubes we swapped all the tubes to all the locations. We did not have the problem no matter which tube went where. We also put an entirely different set of el34s and got the same problem.

We also switch out all preamp tubes as well. At every point of checking we tested all impedance selections just to be sure.

I’m not sure about whether it’s an open loop or not. What am I looking for. Here are the schematics and layout for the amp. The only difference in our amp is I have the B+ grounded to the to the actual ground and the audio grounded to the chassis on the opposite side. We had the ground exactly like the layout too but got the same problem.

https://tedweber.com/media/kits/6o100_layout.jpg
https://tedweber.com/media/kits/6o100_schem.jpg

[M Fowler]

The black wire coming off the reservoir (1st cap) is that the choke?

The last two small black filter caps is the last cap ground connected under the board? It should be grounded along with the one next to it to the buss wire off of pots.

Mark