Ampeg SVT 7 Pro - Static / Buzz

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WolverineBlues

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Feb 27, 2016
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#1
Greetings,

I currently have a used Ampeg SVT 7 Pro on loan from a friend (with the intent to purchase). I believe this one is a Rev C, but its hard to tell because the text on the sticker has rubbed off completely. Since I'm getting a decent deal on this I wanted to see if it would be worth repairing / servicing.

The first thing I noticed when plugging it in is that there is an intermittent static / buzz that occurs when the gain knob is above 12 o'clock. This noise happens when you are not playing as well. I also noticed with higher gain settings, the low end tends to 'fart out' (for lack of a better term) and the gain loses some musicality and richness.

These issues lead me to the 12AX7 preamp tube. What is the general lifespan of this tube in the SVT 7 Pro? Would replacing this tube resolve the issues above? Or should I be looking elsewhere?

Or should I just stay away from this particular SVT 7 Pro?

Also, other than the sticker on the top, is there a way to tell what Revision this amp is? The serial # is also rubbed off...
 
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#2
--- Tubes are funny. Some can operate for years with no problem, some crap out immediately. It's possible there's a tube issue. Also possible that there's corrosion in the effects loop jacks. Plug a cable in between them and see if the problem clears up. If so, spray with Deoxit and that should fix it. If not, back to the drawing board.

--- All of them in recent memory say Rev C on the label. The way to really tell is to look at the motherboard inside. I believe they're on Rev H for the board.
 
#4
JimmyM said:
--- Tubes are funny. Some can operate for years with no problem, some crap out immediately. It's possible there's a tube issue. Also possible that there's corrosion in the effects loop jacks. Plug a cable in between them and see if the problem clears up. If so, spray with Deoxit and that should fix it. If not, back to the drawing board.

--- All of them in recent memory say Rev C on the label. The way to really tell is to look at the motherboard inside. I believe they're on Rev H for the board.
Click to expand...

Thanks for the info! I figured due to the parallel effects loop it should be ok, but I'll check tonight.
 
#5
EASonBass said:
Is the cab you're demoing it with a factor? Tweeter cranked? Over powering causing the farting out?
Click to expand...

The cab is a Sunn (Fender) 410h. Horn is set to 25%. When paired with another head (Carvin R600) the static / buzz is not apparent however. The only other cab I have has blown speakers, so it wouldn't be ideal to test.
 
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#7
So it turns out I was completely off the mark... it ended up being the horn on the Sunn 4x10. I suppose the midrange voicing on the Ampeg brought it out more than the Carvin. I'll just start another thread for that.

Thanks for your help everyone!
 
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