Need Opinion With XTC101B Issue

[lgehrig4]

Hello all! Long time lurker with his first question.

I have an '07 101B and there is a problem with the red channel. I will try to explain everything I observed so please bear through with all the unnecessary details

Bogner XTC 101B
Winged C EL34s
Assortment Chinese/Russian 12AX7s

First, I play at home so the amp wasn't moved around at all. Aside from the Marvel mod I installed, everything is stock. The amp had been working perfectly since I got it about 4-6 months ago.

Two days ago I warmed it up and when I took it off standby there were some large pops (on the red channel). I thought this was static electricity coming from my guitar because the room is dry right now and all my amps can be a little crackly. After a few chords it popped some more, the volume fluctuated a little and then a loud humming noise mixed with the signal.

I immediately turned it off and started checking the tubes. I switched out every preamp with ones I know are perfect and I checked the bias on the PTs. All were around 30mA. After I checked these I played it again and it sounded fine. The next day the same thing happened and this time it did not go away

The problem is ONLY on the red channel. The green and blue channels are perfect. If it's something simple I will fix it myself (I have some experience), but if not I'll take it to a tech, however I would like to bring it to him with some ideas first. I do not want to ship this thing to Bogner in CA. Between the shipping and the lack of warranty and chance of damage it's not worth it.

Please offer your opinions on what you think it may be. If you need me to open it up and check a few things let me know exactly what to do and I will get back with results.

Thanks a lot!
Jeff

[Cameron]

Hello all! Long time lurker with his first question.

I have an '07 101B and there is a problem with the red channel. I will try to explain everything I observed so please bear through with all the unnecessary details

Bogner XTC 101B
Winged C EL34s
Assortment Chinese/Russian 12AX7s

First, I play at home so the amp wasn't moved around at all. Aside from the Marvel mod I installed, everything is stock. The amp had been working perfectly since I got it about 4-6 months ago.

Two days ago I warmed it up and when I took it off standby there were some large pops (on the red channel). I thought this was static electricity coming from my guitar because the room is dry right now and all my amps can be a little crackly. After a few chords it popped some more, the volume fluctuated a little and then a loud humming noise mixed with the signal.

I immediately turned it off and started checking the tubes. I switched out every preamp with ones I know are perfect and I checked the bias on the PTs. All were around 30mA. After I checked these I played it again and it sounded fine. The next day the same thing happened and this time it did not go away

The problem is ONLY on the red channel. The green and blue channels are perfect. If it's something simple I will fix it myself (I have some experience), but if not I'll take it to a tech, however I would like to bring it to him with some ideas first. I do not want to ship this thing to Bogner in CA. Between the shipping and the lack of warranty and chance of damage it's not worth it.

Please offer your opinions on what you think it may be. If you need me to open it up and check a few things let me know exactly what to do and I will get back with results.

Thanks a lot!
Jeff

Does it stop when you pull the 1st pre? or does it stop when you pull the 2nd tube. I think it will stop when you pull the 2nd...if so recheck your work on the mod...check the solder joints.....or just solder suck(always solder suck and clean.....do not just add solder when modding or changing parts) and clean and re-solder. There is also a few other things too... but lets see if this does it.

[lgehrig4]

Ok, when I pulled the 1st tube it was still making noise, but not as loud. When I pulled the 2nd tube it was silent, aside from a very low crackle as I was turning the volume up the first time.

I'm not sure I understand how this could be the connections to the Marvel mod. If the solder joints did not have good contact wouldn't that essentially be like clipping those extra caps on a post '04 making it a pre'04? Also, even if it wasn't the best joint, could this happen out of the blue if the amp was never moved?

[marcoloco961]

Ok, when I pulled the 1st tube it was still making noise, but not as loud. When I pulled the 2nd tube it was silent, aside from a very low crackle as I was turning the volume up the first time.

I'm not sure I understand how this could be the connections to the Marvel mod. If the solder joints did not have good contact wouldn't that essentially be like clipping those extra caps on a post '04 making it a pre'04? Also, even if it wasn't the best joint, could this happen out of the blue if the amp was never moved?

Cold solder joints can be a real bear. They might look fine and even hold the wire or component securely, but only conduct when they feel like it. Usually if a component fails the problem is there to stay. Cold solder joints are normally the culprit when the problem comes and goes. They will usually cause some kind of popping or frying bacon sounds when shorting in and out. I was having some issues with an amp I was working on the other day so I decided to just re-solder all the connections on the pots. Sure enough, they all appeared tight when looking and tugging on the leads, but when I un-soldered one of the connects, I could see that one of the wires was not very well tinned and looked to be losing contact. Once I fixed that, the problem went away.

Found a bad solder joint on a newer VHT at the cathode resistor connection a couple of weeks ago. The amp had been intermittently red plating for over a year and had been to a couple of techs who apparently missed the issue. Once the solder joint was fixed, so was the amp. Not trying to knock your work, but if the problem started after the mod, I would go ahead and re-check my solder joints as suggested. Even the pros get a cold solder joint from time to time.

[lgehrig4]

Ok, so I think I got it. I did what Cameron said. Desoldered the mod, cleans the leads and resoldered, but the problem still persisted.

As I was testing the amp I accidentally bumped the volume knob and noticed that the noise reacted to it so I started wiggling and turning it and sure enough the problem seemed to be in the pot. I sprayed some contact cleaner in the pot and now it is working perfectly.

I'm going to try again later when the amp is not so hot just in case this problem just goes away when the amp it heated.

[Structo]

I would replace that pot.

[lgehrig4]

Not trying to knock your work, but if the problem started after the mod, I would go ahead and re-check my solder joints as suggested. Even the pros get a cold solder joint from time to time.

I'm a newbie so I wouldn't be ashamed of a cold joint. I would have thought it was the mod, but it didn't happen right after the mod as you say. I modded the amp pretty much as soon as I got it and have been playing it for 4 months so it wasn't obvious that it was the mod. Turns out it wasn't the mod (see my earlier post)