Weber 6O100 Build Issues

[csjoyner]

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

Where (specifically) is the best place to switch the PI output?? I was thinking at the master volume pot but I want to be sure. Here is a link to the layout again.
https://tedweber.com/media/kits/6o100_layout.jpg

[sluckey]

Yes, just swap the wires on the wipers of the MV. However, if you've already swapped the OT primary plate leads with no improvement, swapping the PI outputs will do no better.

[luix]

It seems like if the other two tubes start working on signal peaks, are all tubes biased correctly?

Are the socket well soldered and do they make good contact on tubes pins?

[sluckey]

I just noticed that your output tubes are really spread apart. What happens if you pull the two inner tubes and operate only on the two outer tubes?

[jajoyner]

I just noticed that your output tubes are really spread apart. What happens if you pull the two inner tubes and operate only on the two outer tubes?

I pulled the inner tubes. We have no issues with them out. We also pulled the outer tubes. No issues there either. Only with all 4 tubes.

[jajoyner]

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

Pulled the NFB wire from the circuit and still have the popping issue. But now, with the volume at 3 and the master at 9, we are getting modulation. I've attached an audio file I recorded on my iPhone (the speaker I'm using isn't great, but you will get the idea).

[Phil_S]

The problem exists only with 4 tubes and not 2 tubes. Doesn't matter if it's the inner pair or outer pair. You've rolled the tubes, so it's not a bad tube. Here's what this suggests to me.

Power creates the problem. This suggest the problem exists *after* the power section. Really, there are only 2 things: speaker or output transformer. Do you have spares so you can swap them out one at a time? I suppose there could be a problem with B+ caps on the plates and screens. You might reflow solder and/or R&R the caps. Cap changes might be the least cost so think about doing that first unless you have a spare OT and speaker.

[csjoyner]

The problem exists only with 4 tubes and not 2 tubes. Doesn't matter if it's the inner pair or outer pair. You've rolled the tubes, so it's not a bad tube. Here's what this suggests to me.

Power creates the problem. This suggest the problem exists *after* the power section. Really, there are only 2 things: speaker or output transformer. Do you have spares so you can swap them out one at a time? I suppose there could be a problem with B+ caps on the plates and screens. You might reflow solder and/or R&R the caps. Cap changes might be the least cost so think about doing that first unless you have a spare OT and speaker.

It’s not the speaker as it has the same problem on 3 different sets of speakers on all of the ohm selections.

We get continuity on all of the OT wires that should have it. We do not have a spare OT so is there any way to test that?

There is no audible problems when wiggling the tubes and chopsticking all the wires. We have ruled out any specific tube and socket by alternating tubes and sockets when we are only using two. Also, we get the same problem with a different set of tubes.

[romberg]

Where are the 5.6k grid stopper resistors (that run to pin 5 of each power tube) located? Are they mounted on your board like the layout? I can't tell from your pictures.

If they are not mounted directly onto the tubes, I'd move them there. Just mount each resistor directly into pin 5. This is the best location for them to block oscillations that may be picked up on the rather long runs to the grids (which are connected to pin 5). You might also try increasing the values of these grid stoppers. Say to 33k or so. It feels to me like you may have an oscillation related problem (triggered by transients) which grid stoppers may help you solve.

Mike

P.S. You might also try mounting a 47-100pf or so fizz cap across C22 and C23 like is found in marshall/trainwrecks.

Code: Select all

       C22
------||-------+---------------------- to MV
                    |
         C23        =  47-100pf
                    |
-------||------+------------------------- to MV

[jajoyner]

Hi kids! Thanks again for all the suggestions. We won't have time to work on the amp until next weekend (10/16). We will update you when we've given your suggestions a try. And keep 'em coming. We know we are close to solving this and having a working amp...

[csjoyner]

Where are the 5.6k grid stopper resistors (that run to pin 5 of each power tube) located? Are they mounted on your board like the layout? I can't tell from your pictures.

If they are not mounted directly onto the tubes, I'd move them there. Just mount each resistor directly into pin 5. This is the best location for them to block oscillations that may be picked up on the rather long runs to the grids (which are connected to pin 5). You might also try increasing the values of these grid stoppers. Say to 33k or so. It feels to me like you may have an oscillation related problem (triggered by transients) which grid stoppers may help you solve.

Mike

P.S. You might also try mounting a 47-100pf or so fizz cap across C22 and C23 like is found in marshall/trainwrecks.

Code: Select all

       C22
------||-------+---------------------- to MV
                    |
         C23        =  47-100pf
                    |
-------||------+------------------------- to MV

Are you sure the cap numbers in that diagram are right?

[romberg]

Are you sure the cap numbers in that diagram are right?

Whoops! 21 and 22. The fizz cap usually comes after the coupling caps of the PI. Marshalls and Trainwrecks usually use a long tail pair PI. In this case it is a cathodyne. But I don't see why one (fizz cap) would not also work here. Easy to try and see if it helps.

Mike

[csjoyner]

Sorry about the lateness of this reply but things have been crazy over here. We have a winner!! Thank you romberg. The correct answer was the grid stoppers. We moved them from the board as shown in the layout and put them directly before the tube and BAM!!! No god awful pops. We did have some oscillation after that but switching the OT wires solved that. I cannot thank everyone enough for your time and wisdom. The best part of this is how much I have learned while doing this amp. As big as a pain as this amp was it is amazing. The tone is spectacular and if you are looking for a powerful amp, this will do it.

Once again, thank you all. Until next amp.