When I first got the amp I didn't read the little sticker with the tube positions so I misplaced some AT7 with 12AX7 and viceverse, it was working until I drived the amp louder and then the amp make a realy loud ugly sound like something was screaming and tearing at the same time. I turned it off and back on. Channel one was making this strange sound while I was moving the Volume Pot but no sound out of my guitar, channel two was working fine except for Vibrato which wasn't working and still isnt. I did what I should've done in the first place and searched the web for tube postions, removed 1 blown tube at V1 (AT7) and fixed the rest up. now every single tube lights and they're placed as they should but channel one isn't working neither vibrato and the tone is also messed up
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Re: Channel one doesn't work
The 12AT7 is usually the driver tube for the tubes before it ( the input channels ). It can also be the driver for the reverb or tremelo channel. I'm not sure what model of amp you have or the manufacturer but there are plenty of places to look on the internet for info. http://duncanamps.com/index.htm is a good place to start. If you can't find the schematic for your amp try and find one that is similar to give you some ideas. If you don't have the basic tools like a volt/ohm meter and a capacitance tester. You might have to consider a pro to look at it. You will be looking for resistors and capacitors in the same circuit as the tubes that you originally mixed up. If its a hybrid solid state/ tube amp you will also need a transistor tester. Of course good soldering abilities are necessary and ABSOLUTELY do not work on the amp while it is plugged in and make sure you properly discharge the filter capacitors in a safe and proper manner before touching the circuit. All the info you need to sucessfully do it yourself is available at the library or on the net as long as you are confident in your abilities and first and foremost work in an absolutely informed and safe manner. Hope this helps.
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For decent signal to noise ratio your channel faders should be about 75% up. You should set the trims when punching down the PFL button for each channel so that peaks go up the meter to about 80% of max. Your master levels shoulld be from 50 to 80% up. You should be using BALANCED cables (TRS or XLR) everywhere. Your equipment should ALL be powered from a single receptacle or power conditioning module, even if it means running extension cords. Many people try to run unbalnced cables from this to their amps... it doesn't work and noise results. You didn't give us much info on your system so that we could analyze further
Sounds like a problem with the channel itself, if the clean channel works then its not the lead, input, guitar or the drivers. You have to be careful when opening up amps as some can hold a residual charge and there can be danger of electrocution.
I would recommend getting it looked at by a pro, it doesn't sound like an expensive fix.
Do you turn on standby every time and wait for the tubes to heat up first? If you don't, it can severely damage the tubes.
But a common cause of this could be just old tubes. Like any other piece of technology, tubes get old. If you like to play your amp LOUD then they wear out a lot quicker. You have to replace tubes every now and then. Because I'm not there to check out your amp, I can't give you an exact answer but it sounds like that's the problem. This isn't always a bad thing. You can make the sound of your amp exponentially better with nicer, new tubes. Your amp has 12AX7 tubes. Very common tubes to use actually. I'm not sure what kind of music you play, I'm assuming mostly rock and blues. But here is a list of tubes and reviews on them.
This is how to replace a tube:
Upkeep on a tube amp:
A note he doesn't make in the video is to dust out your amp. I use the compressed dust spray for the inside of computers.
So overall, stop turning up your amp to 11, make sure it's well ventilated and dust it out from time to time. Hope this helped.
The power amps may be blown... PLEASE read my tip on Fixya about the hazard with PMP mixers if you use Speakon to 1/4 inch cables. The sleeve or barrel of the Channel A plug is the hot, not the tip. Touch it to ground and goodbye Channel A of the amp.
Do this test: Plug a set of earphones into the Main out L and R jacks and see if audio comes out there. (it will only be in one side of the headphone and not too strong... If both L and R have signal there is a problem with the power amp or its configuration. Make sure the slide switch is up in the MAIN L/R position (top position) If all that is correct, the power amps have probably blown. Repair takes a lot of work and getting parts from Behringer now is really hard. The amp module is an HCA2400 and the only source seems to be FullCompass.com...
There can be any number of reasons for this problem - solve it diagnostically by starting with something that you know is working and work through systematically to the other end.
Test a microphone on a separate amp to make sure it works okay. Check amp and speakers working. Check that all output cables from mixer to amp are working by testing separately.
Plug microphone into a channel on mixer. Also plug in headphones and turn headphone volume control up.
Make sure input sensitivity knob is turned up a bit (say half way) and main output faders (yellow) are up.
Check that channel is turned on (little button just above the channel fader- needs to be pressed down)
press pfl (pre-fade listen) button (next to button to switch channel on)- do you get any sound on main output or headphones or any indicator lights on mixer to show signal is getting that far (eitehr the individual channel metering lights or the main ones in the central section)?
turn off pfl - make sure channel fader (slider) is up - normal position is ) - about 3/4 of way up. Check lights again on individual channel and main output section - any signs?
Is the sub mix button for the channel pressed down - in which case you will need to bring sub mix (red) output faders up as well as main faders.
If you have got signs of signal on the individual channel but not main see if the channel has been routed somewhere odd (like a subgroup of channels).
Plug a working amp and speakers into one of the auxiliary outputs and use the relevant auxiliary send knob (on each channel just above the faders and pfl switches) to pan some signal to that auxiliary out - do you get anything? There is also a headphone socket for listening to the auxiliary channels (with a selector switch /knob to determine which one - make sure it is in the right position) try listening to the auxiliary output with headphones - anything? If yes the problem lies in the main output section.
Check that there is not a jack plug in the insert socket (to route signal through an external effects unit) without a matching return jack being plugged in - if appropriate is relevant effects unit switched on and correctly set up - if unsure remove the insert plug to take it out of the system.
Make sure any mute buttons are not switched in on main outputs.
For the Drive channel you need to use the Drive control AND the MASTER volume control. When the Drive channel is active, the Channel Indicator lamp should be RED indicating the Drive Channel is active. The Drive control knob is used to adjust the preamp volume and distortion level of the Drive Channel. This gives you a clue as to what to check if adjusting the controls doesn't work -- the preamp tubes. Having said that, ONLY try to check these tubes with the amp OFF! Never stick your hand up into the chassis of a live amp. It could be lethal. Your preamp tubes are the ones farthest from where the power cord enters the chassis. They have a rubber like stabilizer on them. They have a tendency to wiggle loose, which is part of the reason for the stabilizer. Again, if you're not familiar with the insides...stay out and get an amp tech to help you.
The Normal Channel only uses the Volume Control to adjust volume.
The user manual is located at: http://www.bugera-amps.com/PDF/Downloads/1960_P0671_M_EN.pdf on page 5;
When the HIGH 1 and LOW 1 (or HIGH 2 and
LOW 2) connectors are used simultaneously,
their sensitivity is the same (both LOW).
This may be your problem however---
Try swapping input chanels to see if the problem follows ther cable or is in the amp.
Assuming it was working before, you may have a short in the cable or a bad component or tube in the amp. Tubes can be difficult to come by. If the other channel works correctly, It may be one of the small tubes. Hope this helps
You may have a switch that may be bad. For the sound level high and low may need new tubes or possibly may not be seated fully into position. These tubes due get quite hot and do get loose over a period of time.Hope this helps.