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Yo, Anyone know the problem with the buzzing that the Jet 12T makes when striking a chord or a G note? Mine is a 2002 model.
Thanks
Dave
Thanks
Dave
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No experience w/ the Ampeg, but here's some ideas for buzz hunting. I'm assuming you mean a rattly/buzzy sound that falls off.
1. Try a different guitar.
2. Try different preamp tubes
3. Try different power tubes
4. Try with speaker far away from amp (but of course connected!)
5. Try with a different speaker
6. Alternately, can you tap or kick the amp lightly to get the buzz to go? If so, replace the preamp tubes, most likely.
To me it sounds like either a guitar problem or a tube problem. The amp itself shouldn't be moving much, but tube internal elements sometimes rattle, buzz or move. Speakers do this sound sometimes too, especially if the voice coil is rubbing or the surround has been quickly repaired.
In other words, it's a moving part. It may not have been one originally (tubes) or it may have been (speaker, guitar) but in any case something is moving in a bad way. If these don't fix it, it could be a microphonic cap, resistor or strange oscillation. I'd put my bottom dollar on one of the above though. -
Ampeg Jet II J12T Buzzing
I've changed all the tubes. Tried another speaker in a separate cab and it still buzzes. Some one posted on guitar nuts about the screen resistors might be bad from someone running with the volume up too high. I was hoping to find someone that had this problem and how it was fixed. I'll try those things you mentioned and see what happens. I think it might be the speaker vibrating the cabinet so much it causes something to rattle and causes a buzzing sound. I'm in the process of putting a piece of rubber between the chassis and where the board mounts to the chassis to help isolate the vibration to the tube board. Maybe I'll try a piece of foam board over the speaker. But that doesn't account for the buzzing in the other cabinet. There was no vibration in the Ampeg at that point. Probably a Asian piece of shit amp.Comment
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Ampeg Jet II J12T Buzzing
Well guys, the problem is R23 and R22. The spec for these two resistors is 100 ohms. I measured 5.225 M ohms on the one. It was the power tube on the far left of the chassis. I felt the tube in operation for a second and it was a lot cooler that the one on the right. Well, with all that resistance there wasn't enough current flow to heat it up. I replaced both resistors and bumped the wattage up to a full watt. I also raised the reisitor up about a 1/4 inch and moved it away from the tube to keep it a little cooler.The resistors cost $1.49 for the pair at radio shack. I also removed the three wires on connector J25 in front of the left power tube. The connectors are rectangular in shape and the terminal on the board is round. It results in a intermittent connection. I soldered the three wires directly to the terminals on the board. I also added a small piece of rubber to insulate the tube board from vibration where the board mounts to the aluminum risers on the chassis. And lastly I added rubber feet to the bottom of he reverb tank. It sounds wonderful now.
Hope this helped you if you have the problem. Better still, do the mod so you don't waste money buying new power tubes.
Peace
UpstairsComment
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Hi upstairsdave, I really thank you for your advice. I came upon your Post recently when my jet j-12t from the 90th was not only buzzing but distorted every Single ton, even the quietest.
I finaly mesured the R23 and 22 to find one at 122 Ohm (Tube nearly glowing) and one Broken to endless resistance (Tube badly working).
Got two 100 Ohm, 2,5W resistors today measuring 107 Ohm both and voila:
A soundwise new amp with all the sweet cleans we love so much, significantly louder than before. It cost 80ct and the way to the friendly store!
Thank you again for your post!Comment
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