Bugera BC-30 low output

[bigdaddydiesel]

Hi, I just picked up a Bugera with issues for a good price. Problem is that the amp has very, very little output with the master cranked. Channel 2 is louder, while channel 1 is barely audible even at max but both are far quieter than 4xEL84 30 watt 2x12 should be -- we're talking below conversation levels. Bias adjustments make no difference, new power tubes made no change, swapping individual preamp tubes yielded nothing, and a new rectifier tube....nada. Possibly a bad power transformer? Anybody have any experience servicing these? I can't find a schematic anywhere. Have a feeling Bugera only wants you to utilize their warranty and send it back or go to a local authorized tech, but neither are an option with this particular amp.

Any tips or experience is welcome. Thanks!!!

[Enzo]

Every manufacturer wants you to use the warranty, that is what warranties are for. Not only does it mean the customer gets his purchase working, but the factory also learns what will be typical failure modes once products are in the field. win-win.

Power transformer? Not likely.

Each channel has an effects loop, so run a cord from the send of a channel over to some other amp for a listen. Does that channel come out OK in the other amp, or is it still weak there? Then try the same test with the remaining preamp channel.

Likewise, plug the guitar into the return of one of the channels - still weak out the speakers? And the other channel?

Unplug the speakers and connect a different cab to the amp, same or better? And are the speakers wired in phase?

[bigdaddydiesel]

Every manufacturer wants you to use the warranty, that is what warranties are for. Not only does it mean the customer gets his purchase working, but the factory also learns what will be typical failure modes once products are in the field. win-win.

Power transformer? Not likely.

Each channel has an effects loop, so run a cord from the send of a channel over to some other amp for a listen. Does that channel come out OK in the other amp, or is it still weak there? Then try the same test with the remaining preamp channel.

Likewise, plug the guitar into the return of one of the channels - still weak out the speakers? And the other channel?

Unplug the speakers and connect a different cab to the amp, same or better? And are the speakers wired in phase?

Howdy Enzo, no offense meant to you personally. My meaning was the practice of companies with disposable products like Bugera, Blackstar, etc withholding pertinent information from techs that don't pay into becoming an authorized warranty repair for companies. Schematics should be shared freely for this stuff. You are spot-on about the merits wrt QC, though.

Anyway, I noticed the effects loops. Knowing that many Marshall amps, Peavey, etc suffer from oxidation of the cliff jacks I would consider that. I forgot to mention that just about every tube is warm to the touch and dim, hence why I went through with replacing tubes to diagnose. The amp takes a Hell of a long time to come out of standby, also. That's why my mind wants to consider it a power issue of some sort.

Edit: I also connected the head to the shop cab and the problem followed so the speakers are not the issue. I will try the effects loops when I'm back in tmrw.

[Enzo]

OK, not sure if by pay into you mean money, it doesn't cost anything to be a warranty center, other than a few companies don't pay as high a rate a we might like.

I of course wish I had every schematic, but I can't fault the companies for their policies. Some, like Peavey, will send you whatever you want. Others, like Fender put some up on their web sites, and will also send most things you request. On the other end Nady will send nothing to nobody nohow. Then there are companies like Behringer and Line 6 who will only send schematic to authorized service centers. Companies who withhold information often do so so help prevent them from being in the liability loop. If company X sends you a schematic, that is tacit approval for you to work in the amp. They have no idea what your skill level is, if any. If you injure or kill yourself, they can be taken to court for liability for that. Also, if there is any desire for some information to be considered proprietary, then issuing it to the public puts the lie to that, and such claims won't stand up well. Not all companies use this position, but I understand when they do.

Just like election time, some folks will be happy to tell you how they voted, while others would never tell anyone. Neither choice is wrong.


I suspect the loop jacks are not the issue, since both would have to be affected in the same way, but the test helps isolate the problem to one section or the other.

Beyond those simple external tests, when I go inside, I make sure my power supplies are present. It may be a power issue, but unlikely the transformer. it is possible of course, but way down the list. I verify the plate and screen voltages are present on the power tubes. Bias is not likely missing, or it would make plenty of sound as it burns up its tubes. I would go down the smaller tubes and check each plate pin for B+ and each cathode pin for voltage commensurate with the expected current.

"Just about" every tube is warm and dim? OK, what about the one/ones that are not? Is ther glow in EVERY tube, and is ther TWO glowing spots in each small tube?

[bigdaddydiesel]

What you say about liability is true, yes. Times we live in where an individual's poor choices can be blamed on others. I was under the impression that Fender tested and charge an annual fee to become an authorized tech, as well as paying pennies on warranty repairs. Half their stuff is on "do not repair" lists anyway, but I digress...

Yes, two glowing spots on every 12ax7 except for one if memory serves. Which one that is in the circuit I have no idea. I only spent a short time with it. That was the first tube I tried replacing with a known good tube but nothing doing. Rectifier is warm to the touch but the power tubes aren't heated at all and rather dim, which I found to be strange inside a 4xEL84 amp. I checked continuity on all the fuses on the board, though did not remove the board caddies so I may be getting a false reading.

Some of the socket pin solder joints looked shit. I may try re-heating them. I know these amps tend to have issues out of the box with bad tubes and solder joints.

[Enzo]

I don't want to derail your thread, so if you'd prefer to discuss this elsewhere (or at all, for that matter), say so.

Fender tests you to see what your competency is. Most companies ask for an equipment list - what scope, meter, generator, loads, speakers, solder gear, etc, do you have? Most companies also ask for photos of shop, store front exterior, customer counter, and parts storag, so they know you are not some kid in a basement. They will be sending you customers, and they want you to represent them well and professionally. No they do not charge for this, I am unaware of anyone who does. Last I checked, and it has been a while, Roland required attendance at one of their servic seminars for certification, so you would have to go to California at your expense for a few days. Years ago when I signed onto QSC, I was required to buy a start up parts collection for about $400. That was a one time. It was specific parts they used that might not be readily available exactly in the parts market. Fender pays I think $50 an hour unless it has gone up again. $50-60 and hour is pretty common. The service center status is free, but I am obligated to take in any repairs of their brands that are presented.

All manufacturers have a do not repair list, it ONLY refers to warranty, it does not mean teh units cannot be repaired in the technical sense, it is strictly a cost thing for the OEM. The list is not remotely the majority of their models, it is only the low end entry level stuff.

Not everyone likes being a warranty station, but I appreciate the steady stream of new customers it sends to my door. I have gotten far more new customers from my listings with Fender/Peavey/Marshall/Crate/etc/etc/etc than I ever did from advertising or yellow pages. "I never knew you were here, I'll be back I have other things to get fixed."



Every 12AX7 but one? Well it only takes one, every part in there has a job to do to make sound, they don't have extras hanging around inside.

If you swapped the tube, then assume the tube is OK. If one side is dark but the other half glows, then pin 9 is getting current and there is probably a break between pins 4 and 5. Or possibly pin 4 or 5 has a spread female socket pin. At this point, i don't care which one it is in the circuit, it has to be made to light, and all 12AX7s are wired the same as to heaters. get that tube to light back up, and I'll bet my lunch money the sound issues will be solved.

[DrGonz78]

Do the heater voltages have one of those molex connectors attached to the board? I know on other versions of Bugera that those molex connections start melting and eventually the heaters do not light up at all. That was a 6260 that did that and the 333XL or something another. Perhaps by the time this amp was designed this would not be an issue any more. Still I would trace out the voltages as Enzo stated and especially the heater supply.

[bigdaddydiesel]

I don't want to derail your thread, so if you'd prefer to discuss this elsewhere (or at all, for that matter), say so.

Fender tests you to see what your competency is. Most companies ask for an equipment list - what scope, meter, generator, loads, speakers, solder gear, etc, do you have? Most companies also ask for photos of shop, store front exterior, customer counter, and parts storag, so they know you are not some kid in a basement. They will be sending you customers, and they want you to represent them well and professionally. No they do not charge for this, I am unaware of anyone who does. Last I checked, and it has been a while, Roland required attendance at one of their servic seminars for certification, so you would have to go to California at your expense for a few days. Years ago when I signed onto QSC, I was required to buy a start up parts collection for about $400. That was a one time. It was specific parts they used that might not be readily available exactly in the parts market. Fender pays I think $50 an hour unless it has gone up again. $50-60 and hour is pretty common. The service center status is free, but I am obligated to take in any repairs of their brands that are presented.

All manufacturers have a do not repair list, it ONLY refers to warranty, it does not mean teh units cannot be repaired in the technical sense, it is strictly a cost thing for the OEM. The list is not remotely the majority of their models, it is only the low end entry level stuff.

Not everyone likes being a warranty station, but I appreciate the steady stream of new customers it sends to my door. I have gotten far more new customers from my listings with Fender/Peavey/Marshall/Crate/etc/etc/etc than I ever did from advertising or yellow pages. "I never knew you were here, I'll be back I have other things to get fixed."



Every 12AX7 but one? Well it only takes one, every part in there has a job to do to make sound, they don't have extras hanging around inside.

If you swapped the tube, then assume the tube is OK. If one side is dark but the other half glows, then pin 9 is getting current and there is probably a break between pins 4 and 5. Or possibly pin 4 or 5 has a spread female socket pin. At this point, i don't care which one it is in the circuit, it has to be made to light, and all 12AX7s are wired the same as to heaters. get that tube to light back up, and I'll bet my lunch money the sound issues will be solved.

No worries. This is a good derail. I must have misheard what a buddy relayed to me about paying into the warranty program. I definitely recall he said he stopped doing warranty work because of long wait times for Fender to pay and some difficulty getting parts. This was back around 2002. Maybe he just fell through the cracks?? I'm an independent luthier by trade but do amp work on the side. Most of it is no-brainer stuff; replacing old or failing e-caps, basic maintenance, or sorting known issues with modern consumer-grade amps. It's something I started a few years ago and every now and then I pick up personal projects to learn on and enjoy.

I didn't jot down on my checklist whether moving the tube that wasn't lighting up made any difference in other positions. I noted the known good tube didn't light up in that one position, but worked in the other 3 and made no difference with the issue I'm having. I'll have to repeat that process to see if there is an issue with that specific tube socket. I will have to look for an owner's manual to find out which socket is what as they're merely labeled 12ax7a, 12ax7b, c etc after tube designations, not actual function...rather unhelpful.

Do the heater voltages have one of those molex connectors attached to the board? I know on other versions of Bugera that those molex connections start melting and eventually the heaters do not light up at all. That was a 6260 that did that and the 333XL or something another. Perhaps by the time this amp was designed this would not be an issue any more. Still I would trace out the voltages as Enzo stated and especially the heater supply.

I recall this issue. There are plenty of molex connectors in here. I pushed down some that appeared to be a little loose. I may try just re-seating each one-by-one.

[Dave H]

Rectifier is warm to the touch but the power tubes aren't heated at all and rather dim, which I found to be strange inside a 4xEL84 amp.

Power tubes should be too hot to touch. I'd check their heater voltage, plate voltage, screen voltage and bias current.

[Jazz P Bass]

Voltage checks.
Voltage checks.
Voltage checks.

I do not see any.

[bigdaddydiesel]

Bumping this to update. It turned out to be a simple repair. the amp i bought was actually a 220v european model that inadvertently made it into the states via Musician's Friend earlier this year. Rather than go through Behringer to order a replacement PT i opted for a step up transformer. Amp works great.