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Post new topic Carvin BX problem. PROBLEM SOLVED
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Author Topic:  Carvin BX problem. PROBLEM SOLVED
George Kimery


From:
Limestone, TN, USA
Post  Posted 12 Mar 2018 5:36 pm    
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While practicing today, my BX 500 developed a distortion prob!em. No distortion at !ow volume, but it is only about half as loud as it should be. I have done all the troubleshooting that I know how to do. I have checked out all the cords, plugged direct from guitar to amp, backed down the pre-gain in relation to the master gain, turned the graphic EQ section off, checked all knob controls, turned the 12AX7 tube to bypass mode, etc. I am assuming that by turning the tube to the bypass position, I can rule out a bad tube, is this correct? Or, if the tube is bad, could there be some bleed through of some sort still causing distortion? I really like this amp and don't want to lose it, but I don't want to go through the getting it repaired ordeal and expense with Carvin, especially since their amp manufacturing is rumored to be no more.

Last edited by George Kimery on 13 Mar 2018 2:11 pm; edited 1 time in total
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Jack Stoner


From:
Inverness, Fl
Post  Posted 13 Mar 2018 2:19 am    
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I don't think its the tube, as mine started some very slight distortion and switching it to "tube bypass" cured the distortion.

But, to be sure remove the tube or replace it and see if it makes any difference. They use an "FET Gate" to add or remove the tube and there could still be a possible bleed through.
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Scott Denniston


From:
Hahns Peak, Colorado, USA
Post  Posted 13 Mar 2018 5:04 am    
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This probably isn't it but worth mentioning. I had an amp that was distorting and I checked "everything" and just about gave up on it. Turned out it was the almost dead 9v battery in my Goodrich volume pedal. That will sound like the amp or speaker distorting badly. Now one of the first things I would do is eliminate the vp.
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Nathan Guilford


From:
Oklahoma City
Post  Posted 13 Mar 2018 1:39 pm     distortion
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Do you use a Lil' Izzy or a Matchbox? If the battery is going on those, you'll get some weird distortion too.
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George Kimery


From:
Limestone, TN, USA
Post  Posted 13 Mar 2018 2:23 pm     Carvin BX problem.
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It was the tube. The amp is a couple years old, so it was due a new tube.

When the bypass tube switch is off or on, the tube stays lit. So the bypass switch is like a standby switch. When I removed the tube, problem solved. Put in new tube, all is back as it should be. So there is some leakage when the tube switch is in bypass mode.But this is a good thing. It lets you know when the tube is going bad.

Thanks for all the help.
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Jon Light


From:
Saugerties, NY
Post  Posted 13 Mar 2018 3:03 pm    
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That's great. Jack nailed it.
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Tom Wolverton


From:
San Diego, CA
Post  Posted 13 Mar 2018 6:04 pm    
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I have this amp in a soft case with a Lexicon MPX-100. It sounds really great. I like the tube too. But I am a little concerned about that tube life. Shouldn't it last longer?
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George Kimery


From:
Limestone, TN, USA
Post  Posted 13 Mar 2018 6:33 pm     Carvin BX problem.
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I got a JJ tube at my local music store for $14.95, so the expense was minimina!. Also really easy to change the tube. Just removed the screws on the top and the plate lifted off. Unplug the old tube, plug in the new.
Five minute job.

As for the life of the tube, I don't know how !omg they are supposed to last. I read a post once where somebody said you need to replace the tubes in a Twin amp once a year. Seems a bit much to me, but it may depend on how much you use it. I don't think you need to be concerned. Eventually you will have to replace the tube, so maybe you should pick up one now (12AX7) so you will be prepared. Put the spare tube in your pack a seat along with a Phillips screwdriver. You could change tubes within two songs of less.
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Jack Stoner


From:
Inverness, Fl
Post  Posted 14 Mar 2018 2:02 am    
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The tube in mine lasts less than a year and starts some (very little) distortion. Replacing the tube does the job.

I corresponded with Carvin support and the problem is the filament voltage. It is low on mine and he told me they changed the value of one of the resistors to bump up the filament voltage. They sent me (free) some of the new value resistors but they are "SMT" type and where its located is crammed in with other components and I was afraid to try and unsolder and solder in the new value so I left it as it is. If I remember correctly, version "L" (version marked on motherboard) has the new value resistor.

Here is a link to a forum post I made about this.
https://bb.steelguitarforum.com/viewtopic.php?t=320877&highlight=
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George Kimery


From:
Limestone, TN, USA
Post  Posted 14 Mar 2018 7:09 am     Carvin BX problem. PROBLEM SOLVED
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Jack, thanks for the link. It was very informative.

I kept the original factory tube, so it dawned on me, this is the 2nd tube I have replaced in 2 years. So my mileage is not much different from yours. I have the amp rack mounted along with a Steelaire. It depends on the gig and my mood as to which amp I use. I also switch from one to the other for practice. I am stopping using the BX 500 for practice to preserve tube life. Thank goodness the tube is cheap and easy to replace. I am going to get a cheap combo amp for practice and save my good stuff and not have to hook up my rack system.I
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