Bugera 333 212 combo, very low output

[Pdavis68]

And there's this:

http://music-electronics-forum.com/t34661/

[bwheat]

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.

[Pdavis68]

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.

[Enzo]

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.

[bwheat]

And there's this:

http://music-electronics-forum.com/t34661/

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

[Pdavis68]

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.

[bwheat]

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.

[Pdavis68]

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.

[bwheat]

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.

[Enzo]

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

[bwheat]

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

[ATTACH=CONFIG]41999[/ATTACH]

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

[Enzo]

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".

[bwheat]

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.

[nosaj]

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

[The Dude]

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.