Gibson GA40 RVT Cutting Out

[daradaramike3]

Hello, this is my first post on this forum but any help would be greatly appreciated.

I purchased one of those new Gibson GA40 RVT amps about a year ago and have had no problems with it until now. However, the amp has started to cut out and lose any volume after about 20 minutes of playing, then come back in after a few seconds with a loud hum and tremolo on, then go right back to normal, only to start the whole cycle over again after a few minutes time. It sounds as if something is on the verge of failing, but I am no expert and therefore cannot be certain this is the case.

The repair shop Gibson has listed in my area has a reputation of shoddy workmanship, and if at all possible I would like to avoid them, but in the end I will most likely have to take the amp in to them.

I was wondering if anybody has any clue as to what may be causing this, or if anybody has had a similar problem. I can read schematics so any help zeroing in on what the problem might be will help me in making sure it is fixed correctly.

I have attached a schematic for the amp that was listed in another thread in this forum.

I know not a lot of people have this amp but any clue as to the likely culprit would be greatly appreciated.

Thank You.

[77custom]

Hello, this is my first post on this forum but any help would be greatly appreciated.

I purchased one of those new Gibson GA40 RVT amps about a year ago and have had no problems with it until now. However, the amp has started to cut out and lose any volume after about 20 minutes of playing, then come back in after a few seconds with a loud hum and tremolo on, then go right back to normal, only to start the whole cycle over again after a few minutes time. It sounds as if something is on the verge of failing, but I am no expert and therefore cannot be certain this is the case.

The repair shop Gibson has listed in my area has a reputation of shoddy workmanship, and if at all possible I would like to avoid them, but in the end I will most likely have to take the amp in to them.

I was wondering if anybody has any clue as to what may be causing this, or if anybody has had a similar problem. I can read schematics so any help zeroing in on what the problem might be will help me in making sure it is fixed correctly.

I have attached a schematic for the amp that was listed in another thread in this forum.

I know not a lot of people have this amp but any clue as to the likely culprit would be greatly appreciated.

Thank You.

Hello,

new guy here. I was wondering if you or any one has seen or knows where to find the correct schematic for the GA40RVT. The attached schematic does not match up to the boards labeling.

Any help will be great. Thanks,

Ed

[indyrocks]

Hello, this is my first post on this forum but any help would be greatly appreciated.

I purchased one of those new Gibson GA40 RVT amps about a year ago and have had no problems with it until now. However, the amp has started to cut out and lose any volume after about 20 minutes of playing, then come back in after a few seconds with a loud hum and tremolo on, then go right back to normal, only to start the whole cycle over again after a few minutes time. It sounds as if something is on the verge of failing, but I am no expert and therefore cannot be certain this is the case.

The repair shop Gibson has listed in my area has a reputation of shoddy workmanship, and if at all possible I would like to avoid them, but in the end I will most likely have to take the amp in to them.

I was wondering if anybody has any clue as to what may be causing this, or if anybody has had a similar problem. I can read schematics so any help zeroing in on what the problem might be will help me in making sure it is fixed correctly.

I have attached a schematic for the amp that was listed in another thread in this forum.

I know not a lot of people have this amp but any clue as to the likely culprit would be greatly appreciated.

Thank You.

Hello, new as well. The SAME EXACT thing has happened to me. After about a year of use, my sound is fading out after 20 minutes, and then comes back after 30 seconds, only to continue to happen. The lights in the tubes go on and off when this happens too. It's definitely not a tube or a fuse. Any ideas here? Thanks!

[77custom]

Sounds to me like it is a cold solder joint. I would go through all your solder joints with a soldering iron.

[daradaramike3]

Its the bridge rectifier for the heater filaments

Hey guys,
The problem for me turned out to be the bridge rectifier for the 6.3 heater filaments. I think Gibson tried to use this to lower the noise floor by feeding the heater supply with DC instead of AC.

I replaced the bridge rectifier with a 10 amp rated unit from mouser electronics and haven't had a problem since. If you open the amp up and look at the amp chassis from the front side, the bridge rectifier in question is in the front right hand corner next to the big tan colored bias cap for the power tubes.

If you search the older threads for Gibson GA42RVT there was a guy, (perhaps by the name of EFK?) who was a lot more diligent about taking pictures of the bridge rectifier, and was the one who originally figured out the problem. His posts will probably be infinitely more helpful than mine.

Hope that helps!

Mike

[indyrocks]

Hey guys,
The problem for me turned out to be the bridge rectifier for the 6.3 heater filaments. I think Gibson tried to use this to lower the noise floor by feeding the heater supply with DC instead of AC.

I replaced the bridge rectifier with a 10 amp rated unit from mouser electronics and haven't had a problem since. If you open the amp up and look at the amp chassis from the front side, the bridge rectifier in question is in the front right hand corner next to the big tan colored bias cap for the power tubes.

If you search the older threads for Gibson GA42RVT there was a guy, (perhaps by the name of EFK?) who was a lot more diligent about taking pictures of the bridge rectifier, and was the one who originally figured out the problem. His posts will probably be infinitely more helpful than mine.

Hope that helps!

Mike

Thanks for the insights Mike! I'm not an amp tech and am still under warranty so I'm going to take the amp to the Gibson dealer where I bought it to hopefully get this rectified. To be honest, I don't know if the guy at the shop will know what to do, he's not a very good tech. Does anyone know if Gibson has been making good on the warranties for these amps?

Cheers
Aviv

[daradaramike3]

Sadly, I couldn't tell you whether or not Gibson will make good on the warranty because I just ended up fixing it myself. As I said in my first post, the only tech in my area has a bad reputation and I have had experiences that have confirmed said reputation. However, since the components are mounted on a turret board and everything is all laid out for you, it really shouldn't be hard for the tech you have in mind to get it done right. It was a 10 minute fix for me and it was my first experience repairing an amplifier.

If I had an even halfway decent tech in the area I would do what you are thinking and just take it in so as not to void the warranty.

Best of luck to you!

Mike

[seanman]

I replaced my Bridge Rectifier, but the fuses keep popping. Replaced my Power Tubes, but fuses keep popping. The amp comes on for a moment, until I turn the standby off. I have no idea what could be doing this. Any Ideas?

[77custom]

I replaced my Bridge Rectifier, but the fuses keep popping. Replaced my Power Tubes, but fuses keep popping. The amp comes on for a moment, until I turn the standby off. I have no idea what could be doing this. Any Ideas?

Take a picture of the bridge rectifier up close for me and post it here. I don't know your ability so could you have put it in incorrectly?

[seanman]

I have powered the amp up with the power tubes removed. The amp stayed on. When I replaced the power tubes, the fuse popped with I turned the standby off.

[77custom]

Was the amp "working" before you replaced the rectifier? What I mean is the fuses not blowing.

[77custom]

It looks to be in correctly, How are your solder joints?

[seanman]

Was the amp "working" before you replaced the rectifier? What I mean is the fuses not blowing.

Yes, The fuses were blowing prior to replacing the Bridge Rectifier. After reading some of the threads, I ordered the Rectifier.

[seanman]

It looks to be in correctly, How are your solder joints?

The solder joints look decent.
I was wondering if the old Bridge rectifier failed, if it could take out the electrolytic capacitors.?

[52 Bill]

Yes, The fuses were blowing prior to replacing the Bridge Rectifier. After reading some of the threads, I ordered the Rectifier.

Did you test anything before you replaced the bridge rectifier? Do you have a meter? How about a light bulb limiter?

You could have a shorted filter cap, or a bad tube socket, or a shorted filter choke, or a shorted output transformer, or a shorted wire connection. Trying to fix this by replacing parts on the off chance that you luck into finding the bad part is a waste of time, money and may cause additional problems from the parts replacements.

Tell us what you have available to test with and we can help you fix your amp.