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Thread: Bugera 333 212 combo, very low output

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    Bugera 333 212 combo, very low output

    Hi guys new to this site, looking for a little advice. I have a 333 212 combo that I am trying to diagnose. It powers on and everything appears to work fine, but I am getting very little sound. I literally have to crank the master up all the way to get a little noise out of it. I tried to bypass the preamp by plugging into the effects loop. This gave me nothing but some popping noises when strumming. Also get a hum and pop when the effects loop is switched on.It seems to me that the preamp is working as I hear some noise, but the power section is not amplifying the sound. This amp already has the power transformer wires soldered directly to the board. I went thru and cleaned the paint from the chassis at the grounding points to rule that out. Also looked the board and capacitors over well and all look fine. The fuses are all good as well. Did a little voltage testing on the power side and everything seemed like what it should be. Trying to find a local shop to test the tubes for me, as they are the original bugera tubes. Any help would be greatly appreciated.

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    Quote Originally Posted by bwheat View Post
    Hi guys new to this site, looking for a little advice. I have a 333 212 combo that I am trying to diagnose. It powers on and everything appears to work fine, but I am getting very little sound. I literally have to crank the master up all the way to get a little noise out of it. I tried to bypass the preamp by plugging into the effects loop. This gave me nothing but some popping noises when strumming. Also get a hum and pop when the effects loop is switched on.It seems to me that the preamp is working as I hear some noise, but the power section is not amplifying the sound. This amp already has the power transformer wires soldered directly to the board. I went thru and cleaned the paint from the chassis at the grounding points to rule that out. Also looked the board and capacitors over well and all look fine. The fuses are all good as well. Did a little voltage testing on the power side and everything seemed like what it should be. Trying to find a local shop to test the tubes for me, as they are the original bugera tubes. Any help would be greatly appreciated.
    What are your voltages for V1a,v2a,v3a,v4a, v5. Voltages with tube in the sockets and with the sockets no tubes.

    Thanks,
    nosaj
    Schematics herehttp://bmamps.com/Schematics/Bugera/...20333%20xl.zip
    pdf64 likes this.

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    I will get some exact numbers for you, when I had it open last I measured the voltage out of the tubes to the output transformer and it was between 425 and 450. I will get the exact voltage though. The red which goes to the output transformer was in the same range.

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    Alright, I got some measurements,

    Without tubes----Pin3/plate, v1 492, v2 492, v3 495, v4 494
    Pin4/screen, v1 488, v2 489, v3 491, v4 491
    pin5/grid, v1 41, v2 41, v3 41, v4 41
    Pin8/cathode, v1 0, v2 0, v3 0, v4 0

    With tubes-------pin3, v1 445, v2 447, v3 447, v4 449
    Pin4, v1 444, v2 443, v3 444, v4 445
    Pin5, v1 -37, v2 -37, v3 -37, v4 -38
    Pin8, v1 0, v2 0, v3 0, v4 0

    Valve 5----without, pin1 439, pin2 0, pin3 0, pin6 438, pin 7 0, pin8 0
    with, pin1 298, pin2 36, pin3 80, pin6 308, pin7 48, pin8 81
    Last edited by bwheat; 01-04-2017 at 10:17 AM.

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    Those readings seem ok.
    How about if the reverb is turned up and the tank is 'agitated'; do you get the normal clang?

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    Quote Originally Posted by pdf64 View Post
    Those readings seem ok.
    How about if the reverb is turned up and the tank is 'agitated'; do you get the normal clang?
    This amp has digital reverb, no springs. I did notice that a few of the preamp tubes have some white buildup at the bottom around where the pins go thru the glass. I found a local shop that does have a tube tester, waiting to hear back on whether not they can test the 12ax7's and 6l6gc's .

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    It looks feasible to apply a signal to the reverb return, so give that a go.
    Do the Vdc on IC1 look ok, ie 15V on 8, -15V on 4, 0V on 7 and 1?

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    Quote Originally Posted by pdf64 View Post
    It looks feasible to apply a signal to the reverb return, so give that a go.
    Do the Vdc on IC1 look ok, ie 15V on 8, -15V on 4, 0V on 7 and 1?
    I will do the test on Ic1 , as for supplying a signal to the reverb return I am not 100 percent sure what you mean, like actually attach a 1/4 jack to that circuit so that I can hook a guitar up up to it, or by jumping the signal from from somewhere else on the board?

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    I think I found the Ic1, there is one on the front board behind the input jack with 6 pins.
    Last edited by bwheat; 01-04-2017 at 12:06 PM.

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    Quote Originally Posted by bwheat View Post
    ...as for supplying a signal to the reverb return I am not 100 percent sure what you mean, like actually attach a 1/4 jack to that circuit so that I can hook a guitar up up to it, or by jumping the signal from from somewhere else on the board?
    Whatever works and is simplest to implement, eg tack in a link wire from the normal input jack socket, fx return, etc to the reverb return.
    Anything to get a signal to the power amp, bypassing the relays and the other stuff that could go wonky.

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    While looking for a place to tap into the reverb I found quite a few differences in the 333xl schematic and what my 333 non xl has. I emailed bugera to see if they have the actual schematic for this model. Waiting back on that. I am getting the tubes tested on Monday. there is an x44 2 pin connector that runs to the power side, it is the closest to the reverb controls, but with the board still bolted in place I can't really see the traces to verify that the reverb circuit is connected to it. Going to find a different type of lighting to see if I can make it out better. These black boards are kind of hard to see the traces from an angle.
    Last edited by bwheat; 01-08-2017 at 09:19 AM.

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    Got a message back from bugera. This place has the worst customer service ever. Basically just said that I am not allowed to repair it myself and it has to be taken to an authorized dealer for repair, and that they can't release anything, or even sell parts. hoping I find a bad tube.
    Last edited by bwheat; 01-09-2017 at 08:22 PM.

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    Senior Member Enzo's Avatar
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    Behringer has never shared schematics, except with authorized service centers, and we had to sign non-disclosure agreements.

    many companies do not sell parts directly to consumers, they rely on their dealer network to handle that. yes, on the other end of the scale is Peavey, who gives schematics to anyone, and wioll sell parts to anyone. You can't call Fender for a part, nor can you call Ford or GM in Detroit fora part.
    Education is what you're left with after you have forgotten what you have learned.

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    Quote Originally Posted by Enzo View Post
    Behringer has never shared schematics, except with authorized service centers, and we had to sign non-disclosure agreements.

    many companies do not sell parts directly to consumers, they rely on their dealer network to handle that. yes, on the other end of the scale is Peavey, who gives schematics to anyone, and wioll sell parts to anyone. You can't call Fender for a part, nor can you call Ford or GM in Detroit fora part.
    I can actually buy the parts for gm or ford though at their dealership, and get acess to all of their repair imformation. I happen to know a little something about that industry, my specialty is automotive electrical diagnostic and repair. They specifically will not even offer you the part even thru their authorized dealer like others companies will. I can get a full schematic on a 2017 50k dollar product but not a 2011 product that is worth 200 bucks. I am well aware how this works. I was just venting a bit.

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    Try swapping the PI tube with one of the preamp tubes. They're all 12AX7, right? I'm curious if the nature of your problem changes...

    I read about a guy who had low volume on a 333XL and it turned out to be a problem with the PI tube.

    Also, look for burns on the molex connectors. Also a common 333XL issue.

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    Quote Originally Posted by Pdavis68 View Post
    Try swapping the PI tube with one of the preamp tubes. They're all 12AX7, right? I'm curious if the nature of your problem changes...

    I read about a guy who had low volume on a 333XL and it turned out to be a problem with the PI tube.

    Also, look for burns on the molex connectors. Also a common 333XL issue.
    I will give that a try real quick before dropping the tubes off to be tested. They are all 12ax7 tubes. The pi is a 12ax7c but from I have read it works the same as a normal 12ax7. This specific amp has had the molex connector from the power transformer to the main pcb removed and wires soldered to the pins. Also going to test out the plate resistors on the preamp like in the link you posted. Thanks for this information.

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    So the molex connector probably burn up already. I've heard these are nice sounding amps, especially for the price, but they seem to be pretty buggy. A 333XL recently came up on CL locally for $250 and I was so tempted to buy it, but my guess is that it's probably got issues and I don't need another amp that needs servicing at the moment.

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    Senior Member Enzo's Avatar
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    The very first Bugera amps had the molex connector. The pins carrying the heater current failed too often, so a factory bulletin specified we cut off the Molex and hard wire it. They at the same time changed production to hard wired there. Most likely your hard wired connections are factory.

    Any tube that says 12AX7 will work, the A, B, C on the end is not a deal breaker. Guys may prefer one brand over another in each socket, but that is taste, like guitar strings.

    having been a Behringer service center, other than the very early failures on Molex pins, the main problem I saw repeatedly was on the small board where the main power IEC connector was. The thermistors didn't hold their solder well, and we had to clean the leads and resolder them. The remainder of the circuit, was reliable and didn't sound bad. Internet complaints made them seem buggy, because guys didn;t know how to daignose the digital switching section.
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    Quote Originally Posted by Pdavis68 View Post
    On this thread the resistor numbers are listed for the preamp plate resistors. Mine is a little different than the xl model, but I found the plate resistors, my question am I looking for the plate #1 pin 6 or plate #2 pin 1? I measured both and got 100k on all the plate2 resistors and 150k on v8 and v7, and 100k for v6 which seems normal according to the schematic for the 333xl

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    You have 4 preamp tubes? V5-V8? It looks like the two halves of the PI (V5) would have 68K plate resistors and the rest are 100K and 150K. So that's probably right.

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    Quote Originally Posted by Pdavis68 View Post
    You have 4 preamp tubes? V5-V8? It looks like the two halves of the PI (V5) would have 68K plate resistors and the rest are 100K and 150K. So that's probably right.
    So I swapped the pi with v7 and it was the same, swapped it with v8 and now it is quite a bit louder, but only on crunch and lead. Not near as loud as it should be though. Clean is still quiet. Tried v6 and the same. It kind of seems like there might be a couple bad preamp tubes maybe. Going to put v7 back in he pi socket and swap the 6 7 and 8 around.

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    Quote Originally Posted by bwheat View Post
    So I swapped the pi with v7 and it was the same, swapped it with v8 and now it is quite a bit louder, but only on crunch and lead. Not near as loud as it should be though. Clean is still quiet. Tried v6 and the same. It kind of seems like there might be a couple bad preamp tubes maybe. Going to put v7 back in he pi socket and swap the 6 7 and 8 around.
    Oh, so it was one of the preamp tubes. Interesting. Well, cool, glad it's just a bad tube.

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    Quote Originally Posted by Pdavis68 View Post
    Oh, so it was one of the preamp tubes. Interesting. Well, cool, glad it's just a bad tube.
    I think it has possibly 2 bad, I dropped the off to get tested, I should know for sure tomorrow. 2 of them have white calcium like buildup inside at the bottom and 2 nice and clean. Seems like maybe a loss of vacuum maybe.

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    White inside the tube is usually a sign of air in the tube, yes, cracked.

    900x900px-ll-859afb8d_p1050653.jpeg
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    Quote Originally Posted by Enzo View Post
    White inside the tube is usually a sign of air in the tube, yes, cracked.

    Click image for larger version. 

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    The 2 look pretty similar to that, but on the other end. The phase inverter and v7 were both like that.

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    It is physical damage, the circuit can't do that to a tube.

    Yes, that was just one example, the white stuff can be on the side or wherever inside a tube. it is oxidized "getter".
    Education is what you're left with after you have forgotten what you have learned.

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    Got the results from the preamp tube test. They all tested good according to this shop. Still kind of strange that the sound gets louder on the lead and gain channels if they are swapped around.

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    Quote Originally Posted by bwheat View Post
    Got a message back from bugera. This place has the worst customer service ever. Basically just said that I am not allowed to repair it myself and it has to be taken to an authorized dealer for repair, and that they can't release anything, or even sell parts. hoping I find a bad tube.
    FWIW A super Reverb I have all the preamp tubes tested good on a jackson 648R tester both halves of the 12ax7.
    But in circuit the 2nd half of the tube had higher voltages as it wasn't conducting as well. Changed the tube to a known good one voltages are good sound is better. This is what the radio guys keep telling me that the ultimate test of a tube is in circuit which is why a lot of them there rarely use them except testing for shorts.

    nosaj

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    A typical tube tester isn't a 100% accurate method of testing tubes. If the tester says it's bad- it's bad. If the tester says it's good, it might still be bad. Substitution is the best method. I'd also wonder if the shop knew what they were doing and how they tested them. I'm not saying they didn't. I don't know who they are. But, as an example, there was a shop here in town that was testing tubes for customers. They didn't even know that you had to test both elements of a preamp tube.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Quote Originally Posted by The Dude View Post
    A typical tube tester isn't a 100% accurate method of testing tubes. If the tester says it's bad- it's bad. If the tester says it's good, it might still be bad. Substitution is the best method. I'd also wonder if the shop knew what they were doing and how they tested them. I'm not saying they didn't. I don't know who they are. But, as an example, there was a shop here in town that was testing tubes for customers. They didn't even know that you had to test both elements of a preamp tube.
    Maybe Dual triode escaped them
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    Quote Originally Posted by nosaj View Post
    Maybe Dual triode escaped them
    Or a Fool and his money are soon parted.

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    Quote Originally Posted by The Dude View Post
    A typical tube tester isn't a 100% accurate method of testing tubes. If the tester says it's bad- it's bad. If the tester says it's good, it might still be bad. Substitution is the best method. I'd also wonder if the shop knew what they were doing and how they tested them. I'm not saying they didn't. I don't know who they are. But, as an example, there was a shop here in town that was testing tubes for customers. They didn't even know that you had to test both elements of a preamp tube.
    That is kind of what I was thinking, maybe they only tested one side of the tube. It is pretty obvious that at least one isn't working properly or else it would work the same when the tubes were swapped around.

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    Tube testers do not put real world conditions on a tube. As was said above, a tester can point out BAD tubes, but it can't really tell you a tube is good. Both sides may have tested OK on their machine.
    Education is what you're left with after you have forgotten what you have learned.

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    Quote Originally Posted by Enzo View Post
    Tube testers do not put real world conditions on a tube. As was said above, a tester can point out BAD tubes, but it can't really tell you a tube is good. Both sides may have tested OK on their machine.
    Is there a good way to actually test that the tube is doing what it is supposed to when it is in the amp. I have thought about buying some cheap Russian reflector brand tubes just to test this thing out and keep them as spares.

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