Joch230
202 posts
Jun 28, 2010
6:11 PM
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I got a 12AY7 electro harmonix tube to swap out with my stock tube. I pulled the long stock tube out and took off the little spring tube holder off as well. Slid out the old tube, slid in the new. Turn amp on...get lights but no sound at all. Figured I got a bum tube. Put the old tube back in. Tube lights up but still no sound with the original tube either. I didn't even touch anything else. The speak wires are all connected.
What gives? Was wondering if a fuse somehow blew but I'm not positive where to look. Worthless manual. Looks like the outline of a fuse taped up in black cover over one wire.
Could use some advice.
Thanks
-John
Last Edited by on Jun 28, 2010 6:53 PM
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barbequebob
986 posts
Jun 28, 2010
6:22 PM
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If this amp has a rectifier tube, that`s usually what happens when it finally wears out.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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Joch230
203 posts
Jun 28, 2010
6:55 PM
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Bob. The amp is almost new. I don't think I could have worn anything out yet. I just wanted to try it with a tube that would kill the gain a bit.
-John
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Mission Amps
6 posts
Jun 28, 2010
8:28 PM
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Ha ha... OK I'll bite if you're not pulling our collective legs here. ;>)
The long skinny one is an EL84/6BQ5, the power output tube.
The shorter squatty one is the 12AX7.
There is no tube rectifier, it uses a solid state full wave bridge.
http://www.muzique.com/news/images/Epi1.gif
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Bruce
Mission Amps
soulkicker@missionamps.com
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Baker
67 posts
Jun 29, 2010
2:54 AM
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Yes, I have made this change to mine. It is the shorter tube under the spring loaded cover you need to change. you shouldn't need to touch anything else.
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Joch230
204 posts
Jun 29, 2010
4:51 AM
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Bruce/Baker...I had swapped out the one called EL84/6BQ5 with the new 12AY7. I guess that's mistake #one. Now that I look at it, the shorter bulb is under a metal cover like Baker says. Is that a push in and twist kind of thing to get out?
My worry is that I put the EL84/6BQ5 back in where I took it out. Everythings would be back to original. Everything lights up but I get no
sound. I wonder if I blew a fuse. I can only see what looks to be a fuse on a orange wire...only it's like shrink wrapped in black plastic to hold it in place. No easy way to change or inspect it.
Appreciate any advice.
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Baker
68 posts
Jun 29, 2010
5:23 AM
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To change the preamp tube you need to twist the cover, it is spring
loaded and so should pop up. The tube has straight pins in it so just pull it straight out (you may need to give it a wiggle but be careful not to bend the pins in case you want to put it back at some point). This tube should be the same size and shape as your new 12AY7 and I believe it is labeled 12AX7A (I may be wrong on this).
When putting the new tube in, make sure the pins are lined up properly with the holes and just push it in, be very careful not to bend the pins. Then replace the spring loaded cover buy pushing down and twisting the opposite way you did to take it off.
I am not expert when it comes to amps or any electrical stuff so I can't tell you what the result of replacing the power amp tube with your 12AY7 might have been. I suspect it may have blown something out.
Hope this is some help.
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Joch230
205 posts
Jun 29, 2010
5:30 AM
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Thanks Baker. I took the cover off. I'm thinking I may have blown out the original 12AX7 tube. I will try putting the new 12AY7 tube where I was supposed to put it in the first place. Hopefully, I didn't blow out all the bulbs or toast something else. Darn...newb mistake. The fuse situation on these amps is a really poor design from what I'm getting when googling it.
-John
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Greg Heumann
598 posts
Jun 29, 2010
7:30 AM
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I recently had a customer put the EL84 where the 12AX7 goes and vice versa in a Kalamazoo. Smoked the rectifier tube and blew up a resistor. Don't know what happened to you but in general putting tubes in the wrong place is a bad idea.
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/Greg
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barbequebob
988 posts
Jun 29, 2010
10:26 AM
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Now this is a classic reason why you replace tubes one at a time rather than take a bunch out and forget where they go. Preamp tubes are nearly always smaller than a power tube or a rectifier tube and it's also why many companies have a tube chart listing the exact order of where they go and which tubes and too often many people don't pay attention these little details.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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Joch230
206 posts
Jun 29, 2010
6:22 PM
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The damn fuse for the Valve Jr is soldered on each end to the wire. What a pain in the butt...
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harpwrench
304 posts
Jun 29, 2010
6:56 PM
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If everything lights up it's not the fuse anyway, at least on any amp I've let the smoke out of:)
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Joe Spiers Harmonicas
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