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Topic: did i change the right tube? |
Mike Bowles
From:
Princeton, West Virginia, USA
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Posted 20 Feb 2014 10:14 am |
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i changed the 12ax7 4th small tube over to a 12au7 jj for the reverb send the 12au7 got real hot so i put a 12ax7 new back in did i do something wrong?
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Mike Bowles |
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Tom Wolverton
From:
Carpinteria, CA
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Posted 20 Feb 2014 12:07 pm
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What kind of amp is it?
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To write with a broken pencil is pointless. |
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Mike Bowles
From:
Princeton, West Virginia, USA
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Posted 20 Feb 2014 12:38 pm tube
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tom its a 75 fender twin 100 watt i wanted to tame the reverb down a little. i might add that its a silverface master volume.
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Mike Bowles |
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Tim Marcus
From:
San Francisco, CA
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Posted 20 Feb 2014 1:47 pm
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I would leave the 12AT7 in place to the right of the reverb transformer (facing the rear) and put a 12AT7 in the socket to the left of the reverb transformer as well. That will dial back the reverb and get you a little more range on the channel 2 volume knob.
The reverb transformer is the small transformer that is mounted at a 45º angle towards the rear of the amp
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Milkmansound.com |
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Tom Wolverton
From:
Carpinteria, CA
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Mike Bowles
From:
Princeton, West Virginia, USA
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Posted 21 Feb 2014 8:27 am tube
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thanks guys i will do a little experimenting today i changed some tubes yesterday now the microphonics are gone amp is quiet i can run the reverb up to 5 although i never use that much.
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Mike Bowles |
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Mike Bowles
From:
Princeton, West Virginia, USA
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Posted 21 Feb 2014 8:28 am tube
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thanks guys i will do a little experimenting today i changed some tubes yesterday now the microphonics are gone amp is quiet i can run the reverb up to 5 although i never use that much.
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Mike Bowles |
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Mike Bowles
From:
Princeton, West Virginia, USA
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Posted 21 Feb 2014 3:16 pm tim
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my twin has left of the small transformer a 7025 and to the right it has a 12ax7eh i only have 1 12at7 left do i just need to order 2 new ones? they seem to be getting to warm i really dont know much about tube amps except that i really like this twin. i sure dont want to burn it up. thanks for any help.
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Mike Bowles |
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Tom Wolverton
From:
Carpinteria, CA
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Posted 21 Feb 2014 4:21 pm
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Note 7025 is essentially the same as a 12AX7
Note where the 12AT7 tubes are located.
The 12AT7 furthest away from the power tubes is V3. This is the reverb send tube. I changed it to a 12AU7. It makes the range on the reverb dial more useable. But while you are debugging, best to leave the 12AT7 in there.
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To write with a broken pencil is pointless. |
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Tom Wolverton
From:
Carpinteria, CA
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Posted 21 Feb 2014 4:46 pm
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Maybe a stupid question: but aren't the preamp tube heaters all connected? A preamp tube in the wrong location shouldn't get a lot hotter, should it?
Unless something else is off with the amp. Or that particular tube is bad???
Ideas, anyone?
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To write with a broken pencil is pointless. |
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Mike Wheeler
From:
Delaware, Ohio, USA
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Posted 21 Feb 2014 5:05 pm
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All the 9-pin tube heaters are connected together. One 9-pin tube should not get noticeably hotter than another 9-pin tube. If one does get hotter than the rest, then, yes, it could be a bad tube.
If you swap the hot tube to another location, and it still gets too hot, you have a bad tube. If the tube you swap into the hot tube's location now gets too hot, you have a circuitry problem.
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Best regards,
Mike |
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