- Amps [BG]
|JellinWellen ||09-29-2013 11:27 AM |
Crazy noise from bright switch
So my vb-2 has a bright switch on it and whenever I'm on the clean channel I can switch it on and it's dead silent. But whenever I'm on the OD channel (gain around 11 o clock, not very high) if I hit that switch I get this hum and hiss from hell sound out of it. My bass needs to be grounded and shielded and ill be getting that done on Tuesday, is this a common issue with the amp?
What's usually the culprit of this? I never really use the bright switch but I can't help feeling that the amp shouldn't do that.
|nashvillebill ||09-29-2013 11:32 AM |
Do you get the same noise without the bass (and instrument cable) plugged into the amp?
|JellinWellen ||09-29-2013 11:42 AM |
Yeah I do, it's a lot worse with the guitar but its definitely noticeable.
Really starting to regret the purchase of this amp.
|nashvillebill ||09-29-2013 11:57 AM |
Might be a bad preamp tube. OD channel really pumps up the gain so any hiss or hum will be amplified.
I don't have a schematic, BbbyBld can tell you which tube(s) is(are) used on the OD channel.
No reason to regret buying the amp!
|JellinWellen ||09-29-2013 12:02 PM |
I actually just had warranty repairs done on this amp, they said there were issues with the power tubes and they ended up replacing all 6 of them. I asked about the preamp tubes and they said there were no issues as far as they could see.
I'm regretting it because this is my 2nd vb-2, and I just had my current one in the shop for month and it still has issues.
|nashvillebill ||09-29-2013 12:03 PM |
Looking at the manual, the OD is tube half V2b. But the manual doesn't say which 12AX7 is V1 and which is V2.
Try swapping the two 12AX7 tubes--the two tubes next to each other-- with each other.
|JellinWellen ||09-29-2013 12:06 PM |
How would I go about doing that? I have no idea how to open this amp other than from the back which means I would have to take out the power tubes and I don't wish to do that.
I don't want to take it back to the tech who worked on it for the last month, but since they took so long now my warranty is up and I have no choice.
|nashvillebill ||09-29-2013 12:31 PM |
I have not worked on the VB-2, but from looking at the manual, it appears that once you remove the back, it would be possible to reach around the power tubes and get to the two preamp tubes.
Worst case. you remove a couple of the power tubes. They pull straight out and re-insert just as easily.
edit: Looking at a picture of the back, looks like there are 4 screws to remove the back grill. Then all of the tubes are accessible.
edit again: You may have to pull two of the power tubes to reach around the transformer. Disregard the small tube immediately in front of the power tubes, that's the phase inverter. The two preamp tubes have tube shields around them: rotate the shields slightly and the shields pull off. Then the tubes pull straight up.
|JellinWellen ||09-29-2013 12:41 PM |
Ok and I just try the amp with only one 12ax7 plugged in? Or do I switch them around
|nashvillebill ||09-29-2013 12:44 PM |
Switch them around.
|JellinWellen ||09-29-2013 12:49 PM |
Ok well I just took the back panel off, i can't really get my hand past the transformer. If I take the power tubes out. Do I need to rebias them?
|nashvillebill ||09-29-2013 12:52 PM |
Just put the power tubes back in the same socket they came out of and I guarantee you will be OK.
|JellinWellen ||09-29-2013 12:53 PM |
Ok I was able to get the shields off one of the 12ax7s, but it appears the tube is screwed in as the tube does not come out easily at all and I am afraid to exert to much force trying to yank it out. I have not removed any power tubes.
|nashvillebill ||09-29-2013 12:55 PM |
It's not screwed in, they push straight in. Tight is good.
Wiggle the tube side to side slightly as you pull up. They will pull out.
|JellinWellen ||09-29-2013 12:59 PM |
Ok well I tried that, it does not budge. It seems to be in some sort of screwed in mounting.
|nashvillebill ||09-29-2013 01:03 PM |
No, they are merely pushed in. Remove a couple of the power tubes if you have too so you can get a good grasp of the tube without breaking a power tube.
I have had some tubes that were very tight and hard to pull, but there's nothing else holding them.
|JellinWellen ||09-29-2013 01:11 PM |
Ok I swapped them, there appears to be no difference.
|nashvillebill ||09-29-2013 01:12 PM |
Did you have both tube shields on when you tried it again?
|JellinWellen ||09-29-2013 01:28 PM |
|JellinWellen ||09-29-2013 01:33 PM |
I also tried it without the shields, no difference.
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