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Re: Magic 10

9/11/2004 6:06 AM
Re: Magic 10
Hi The V-4 B uses a 12DW7 in one of the preamp stages. it is a lower gain tube. also the there is a 12AU7 tube for the driver tube. another lower gain tube. If they have been subed with 12AX7's you will have less headroom. I run my Svetlana 6L6's at around 30 ma. maybe you just need a louder amp.
9/11/2004 6:32 AM

You really should be able to run this amp more than 3 and get more clean from this amp. I checked the jamesgang bias calculator. at 540 volts and 70% disapation , for class AB each tube should run at 25 ma. also I replaced the wierdo 6K11 tube and that helped alot. you can get one from antique electronics supply
9/11/2004 6:27 AM

The 12DW7/7247/ECC832 are readily available these days, so if you need one you can get one.
9/12/2004 9:19 PM
Paul Drexhage Re: Headroom in Ampeg V-4B
I appreciate all the help guys. FWIW, the tubes are all the "correct" ones, brand new JJ tubes (with the weird military designations EC-whatever). I linked my friend (the owner of the amp) to this board in the hopes that he could make a decision about what to do. I may take the 'scope to the outputs and see exactly where it's breaking up, and to rule out an mechanical noise (it shakes the room). Can anyone tell me though what the rated "clean output" is? That is, I know the thing will push 100+ watts, though I'm not sure if this is undistorted output.  
Thanks for all your help,  
9/13/2004 3:27 AM

At its rated output it will be fairly clean. The whole point of Ampeg amps was strong, loud as hell, clean.  
And those ECC numbers are neither weird nor military. That is just the European numbering system. ECC83 is just the Euro number for 12AX7, for example.
9/13/2004 7:52 AM
Re: Ground fault Ampeg V-4B
I had a problem with noisey controls on my amp. I found that the front control plate was not screwed tight to the chassi. tightened the screws and the amp came to life. the 6k11 is a new old stock tube.  
I'm not sure about the amps rated output. running the power tubes at 70% disipation class AB will give you more clean headroom.  
9/13/2004 4:20 PM
Paul Re: Headroom in Ampeg V-4B
My mistake, Enzo, thanks for the info. I know most JJ/Tesla tubes are labeled in this manner.

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