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Old 03-27-2013, 10:04 AM   #1
joer526
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NAD Hooray! maybe not...

I recently picked up an Epiphone Galaxie 25 all tube amp. It is my first tube amp so I don't really know much about how they perform. It was a great deal and I bought it after only hearing it played clean. It only has a clean channel, no gain knob at all. When I turned it on at home, I heard the same great clean sound I had heard before. The possible trouble was when I kicked on the distortion pedal. The sound kind of hesitated and sputtered as if the tubes couldn't handle the drive from the pedal right away. I kicked it off and the great clean came back. I didn't get to do any more with it as my wife came home and you know what that means.

Yesterday I did some more experimenting and it seemed to perform better. Great cleans, raging distortion and OD, but the trouble was present again sometimes when kicking on the OD pedal quickly. The amp doesn't immediately respond. Is this in any way normal? I figured the problem the other night was that it wasn't warmed up enough as I had just brought it in from a freezing cold 20 minute ride home and turned it on 10 minutes later.

Any thoughts or ideas are appreciated. I have a little time to decide if I'm going to keep it or not. Thanks.
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Old 03-27-2013, 10:21 AM   #2
ProphetToJables
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I would assume the problem lies with the pedal, not the amp.
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Old 03-27-2013, 10:32 AM   #3
joer526
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The pedal works just fine thorough other amps. It also works fine through this amp if I kick it on and don't expect immediate results.
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Old 03-27-2013, 10:44 AM   #4
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Quote:
Originally Posted by joer526
Is this in any way normal?


Nope. Or at least, not with any tube amps I've tried (I haven't tried yours).
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Old 03-27-2013, 10:47 AM   #5
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How are you powering the pedal and the amp? Are they both running from the same plug socket if you're using an adaptor for the pedal?
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Old 03-27-2013, 11:01 AM   #6
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They are plugged into the same power strip.
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Old 03-27-2013, 11:56 AM   #7
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Try using different power points for each one and see if that causes the problem to go away.
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Old 03-27-2013, 08:28 PM   #8
joer526
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So when I got home from work tonight, I pulled all the tubes to inspect them and reseated them. I noticed on one of the power tubes what looked like a burn spot. Is this normal or could it be an indication that it is bad or is going bad?

Also, the tubes are mounted in two sets of 3. I know it has 2 EL84 power tubes, 3 12AX7 preamp tubes, and 1 12AT7 tube for the reverb. I expected to see all 3 preamp tubes together, and the power and reverb tubes together. This was not the case. there was a 12AX7 with the power tubes and the 12AT7 was on the other side with the other two 12AX7s. Does this seem right? I can't find any information on what tube goes where.
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Old 03-27-2013, 08:40 PM   #9
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You should have spares anyway. If you had you could have tested them by now.
The 12AX7 near the power tubes will be the phase inverter which is actually part of the power amp, not the preamp. Just remember where the 12AT7 goes, maybe write on the chassis near it with a Sharpie so you won't mix them up.
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Old 03-27-2013, 08:54 PM   #10
joer526
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I can get some new tubes, but I was hoping to troubleshoot the problem before shelling out the cash in case I wasn't going to keep the amp.

Is the tube replacement something I should do on my own or do I need a tech to do it. I've read of biasing and don't know if I'm equipped to do that. Is that necessary or can i just swap them out?
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Old 03-27-2013, 08:57 PM   #11
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That amp has an adjustable fixed bias with a separate pot for each power tube. It should be rebiased. The preamp tubes don't need to be rebiased.

Here's the schematic.
http://www.blueguitar.org/new/schem..._Galaxie_25.pdf
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Old 03-27-2013, 09:12 PM   #12
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That means I can't just pull and replace power tubes, correct?
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Old 03-27-2013, 09:14 PM   #13
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Pretty much, yeah. They may work but you are taking a risk.
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