#1
ok, i should probably establish that im a bit of a noob with tube amps and pedals. i bought an mxr 10 band eq and put it in my fx loop, only thing about that is, i have to turn the send/cut level down so low to run it that when i switch the fx loop off, there is a major volume difference, which is obviously not good. if i turn the send/cut level up to where the volume is the same between channels, it clips terribly when the fx loop is on and sounds like my speakers are blown. ?? even running the eq flat doesnt help. and on top of all that, i have some serious buzzing happening when at rest, whether the fx loop is engaged or not. i even run a decimator and it is still very very noisy. even when i use my pickup switch like a kill switch, it's still noisy. and its like that with all of my guitars....are these problems related? what can i do here? please bear in mind im new to all this and learning as i go here.....everyone was new once. thanks!
#3
its a bogner uberschall, blue revision. its either an '06 or '07, i just bought it and i talked to some friends of mine that i trust and the basic consensus is that its obviously not easy to do without being there to hear it and trouble shoot. but i was told to start by making sure the power tubes are seated well before i even turn on, then if all looks on the up and up there, turn it on stby for a bit and then check brightness on the preamp tubes and power tubes, checking for bad news there. if all is ok there and i still get the issues, i think it's off to the shop maybe? thank god for warranties. it may be due for a tube change anyway, does anyone know what bogner used in '06-'07 as stock tubes for this amp? it wouldnt surprise me if they were the originals as i bought this thing at guitar center....i have to question a guy who trades a bogner in at guitar center. which is why i bought the pro coverage in the first place.....
#4
Well first of all you have a level mismatch. Your amp likes to see higher signal levels in the loop. It also sounds like the loop return is always active and the loop switch only affects the send.

Lastly the return probably has a low impedance and that *may* cause the pedals to make noise. Are you using a battery or power supply? The pedals may want to see a higher input impedance on what they are driving. This is of course a guess but when you mismatch circuit levels and impedance it's possible for things to go wrong.
#5
i use a power supply. no batteries. and you say my amp likes to see higher signal levels...im not sure what this actually means, but if it means turning up my levels on my effects, the clipping gets worse with the increase in level. and i dont think it's the pedals making the noise, it makes the loud hissing sound even when i plug straight in and dont have any pedals in front or in the loop. ?
#6
Edit: this took like an hour to post due to distractions so also listen to fly135 - he may be on to something there.


I see.

Well, the Pro Coverage should help. I'm tempted to tell you to just utilize that. Not sure why you wouldn't. Yes, making sure tubes are seated and not super bright is good advice. Dying power tubes will usually manifest themselves as volume loss. Dying preamp tubes can manifest themselves as noise, buzzing, squeeling, or all kinds of different noises. You mentioned something also about the FX loop being especially noisy when engaged. I bet that amp has a tube driven FX loop. Have you heard of 'tube rolling'? That is what I would do. Get one or 2 decent preamp tubes, like a JJ and a Phillips 5751.

As far as power tubes, I don't know what originally ships with Ubershalls but I'm guessing KT88s. Just read what tubes you have now both pre and power and write that down for us. Both brand and type. V1 preamp will the one furthest away from the power tubes and go V1, V2, V3, V4....

I'm also not sure if you need to bias this amp for optimum performance but that is needed as well. Google it if you are not sure.

As you go through this process what I would do is hit all the tube pins with a bit a contact cleaner as you go.

Also, make sure that swapping tubes will not negate your GC pro warranty thing. I doubt it.

BTW - never touch the inside of the chassis (the part will all the wires and components) it could shock you pretty bad. You can touch anything on the outside of the chassis.

I'm not an amp tech but I hope this helps a bit. I can give you more info on tube rolling and biasing if you like. It is also possible you have a grounding issue, cold solder joint or component issue. The good news with tubes amps is that most issues can be boiled down to the things I've mentioned so far.
Last edited by 311ZOSOVHJH at Feb 28, 2012,
#7
If you want to test the loop itself just run a patch cable from send to return. If that sounds ok then your problem is most likely simply a matter of balancing your levels into and out of the EQ. You are probably just overdriving the EQ.
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#8
i can find out tonight for sure when i get there, but i know it has EL34's (JJ's) in the power section and 12ax7b's for the pre-amp, i think those are JJ's as well, but im not certain on those. and is rolling swapping out one preamp tube and then bumping each one over to the next valve? i have heard of doing that, im just not sure if this is called rolling.
#9
ok, the el34's are indeed JJ's. the pre tubes are cheap chinese tubes. i opened the back up and saw that the tubes in v1, v3 and v5 are dimmer when the amp is on and have a cloudy white/gray ring on the bottom. i do happen to have 3 engl replacement 12ax7b's, should i swap these out ?
#10
^ yeah, you're close

Edit: Sorry, slow posting. I'll read your last post.


basically take a known, preferably new, preamp tube and stick in V1 - make a note. Take it out, put original back. Put new one in V2 - make a note. etc etc on down the line.

This is not tube rolling but may help you a bit. Good test. A new JJ preamp tube is like $15 and you can always use some anyway.

a little demo I did
Last edited by 311ZOSOVHJH at Feb 29, 2012,
#12
Quote by arteestic1
ok, the el34's are indeed JJ's. the pre tubes are cheap chinese tubes. i opened the back up and saw that the tubes in v1, v3 and v5 are dimmer when the amp is on and have a cloudy white/gray ring on the bottom. i do happen to have 3 engl replacement 12ax7b's, should i swap these out ?

Dimmer doesn't mean all that much. I don't expect preamp tubes to light up evenly. Some are so dim you'd think they are dead. Only super bright is what I worry about. Yes, start swapping some preamp tubes around but take your time and try to keep track of what you are doing. You can actually write 1, 2, 3 on your tubes with a permanent marker if you want to make sure you keep track of what is what.

If anything really funky happens - put all the original tubes back where they were.

Try the FX loop stuff too.

Find the Ubershall user manual and tell us what the preamp tubes do.

If you have any of those rubber jar openers or rubber oven 'mits' they work great for taking out hot tubes. Otherwise, let them cool down and use a glove.


You technically do not need to turn off the amp each time you swap a preamp tube, but that is probably best. Make sure you will not negate your Pro warranty.

Basically just forget I said that last part. I'm not an amp tech.
Last edited by 311ZOSOVHJH at Feb 29, 2012,
#13
ok, so last night, i took out every tube, pre-amp and power one by one. blew out the sockets with on of those air duster things, put contact cleaner on the pins and replaced. i also replaced the 3 tubes i talked about earlier with the engl's. the tubes i took out weren't microphonic, but there was white cloudiness at the the bottom of all 3 tubes. it def seems to sound better. the hiss isnt as noticeable, it's still there, but less annoying than usual. i think im going to replace the other 3 and see what happens.
#16
just found this on Rig-Talk....it was for an Ecstacy though but this was the kind of info I was talking about. I'm sure yours is similar.



V1: 1st stage for all three channels, 12ax7

V2: 2nd stage for 2nd and 3rd channel, 3rd stage for 3rd channel, 12ax7

V3: 3rd stage for 2nd and 4th stage for 3rd channel, 12ax7

V4: Loop, in circuit only if effects loop is on, 12ax7

V5: Phase Inverter, 12ax7

V6: 2nd and 3rd stage for 1st channel, 12ax7

I have some 12ax7c that are 8th gen if ya wanna supercharge that puppy!!!!