Bugera 6262 head(ache)

[Guitarded]

Hey all, I just pickup a Bugera 6262 head and the clean crunch channel work fine.
When I switch to the lead channel I can hear the relay switch over and the lead light comes on but the sound is thin and the lead channel control pots have no effect on the sound but the Clean channel pots will change the sound of the lead channel when lead channel is enabled. also the lead reverb has no effect and the presence control pot has some affect but very weak.
I've got schematics and have had training in electronics but it's been about 25 years since I've work in the industry.
I'm thinking bad lead channel transistor.

Any help or direction would be appreciated.
If you need any more info Ill do what I can.


Thanks

[Chuck H]

It sounds like one or more relay contacts aren't engaging with the switch. It could be a bad relay/s or a problem with the power supply or rail that operates them. It could be as simple as a broken or loose cable contact.

Another possibility is that a component or control specific to the lead channel is failed. I don't mean to be vague. It's just that you may not get a response that is perfectly relevant to your specific symptoms.

[soundguruman]

Relay failure will cause that to happen.
However the relay may be OK, just the voltage is not high enough.

The ones I saw had a pulse relay. The pulse switches the latch contacts on the relay.
If the voltage is not high enough, it won't latch.
However, this type pulse relay is very high reliability (the relay itself).
Much higher standard than "typical" guitar amp relays.
Without 15 volts, it won't latch.

You have to make sure your 15 volt regulator is supplying the full 15 volts.
Inadequate heat sinks on these amps cause the 15 volt regulators to overheat and fail.
(the regulator may have NO heatsink)

The reg overheats and the voltage drops way low...no longer supplies 15 volts.
They are also soldering a BIG resistor across the regulator, in a lame attempt to stop it from overheating failing...

I just move the 15 volt reg to the chassis, with long leads. This provides a good heat sink.
The 15 volt regulator stays real cool and keeps on working.
Once the reg has a heat sink, it no longer needs the big bypass resistor. You can leave that out.

Once the 15 volts stays on...and does not overheat...
and the relay is good, (put in a socket if you pull the relay)
Should switch over and the controls should work.

Another issue is grounding.
These amps depend on poorly designed ground connections.
The plated board contacts a screw post for the ground. Depends on the screw to make tight contact.
These type grounds fail easily and are unreliable. The contact oxidizes, burns, or the screw comes loose.

Bypass the ground - solder a wire to the board - ground with a wire to the chassis, use a ring terminal, nut, screw, lock washer, to make a solid tight permanent ground.

The amp is actually a pretty good sounding one, once you fix the bugs.

[km6xz]

Bugera uses 24 volt relays for that model. The small switching transistor T2 turns on the relay by completing a return path for the 24volts on the relay. If the Bright LED lights when switching, forget the relay as the problem, the same relay(RL2) controls that also.
The relay might be working fine which shifts the attention to the audio path. Check the signal level at the top of the Lead Gain pot, if it OK, check that V7 and V8 are lit, since those two tubes are unique to the Lead Channel. If the tubes are lit, and the Bright LED lights when tuned on Bright, than check for grid signal on pins 2 and 7 of V8, and if OK, pin 2 of V7. A total of 5 measurement or status checks should isolate the defective stage this way.

[Chuck H]

Damn Stan! You wrote that like you've fixed a dozen of them and memorized the schematic or something

[Guitarded]

I knew this was the right place to go. Thanks for sharing your expertise.
I will go through it this weekend.
I will update with findings and result.

[km6xz]

I just looked at the schematic, it is a straight forward simple circuit that is suitable for making an educated guess of operating conditions at every node.
Bugera is one brand that did not exist when my shop was the western half of the US depot maintenance for Behringer but I am sure we would have done a thousand of them if it was out 11 years ago. I see different models of Bugera from rehearsal studios who are tough on them, but do not know any user/owners of them using them for personal playing. With decent tubes, they sound a lot better than their price would suggest. They come with really if'y tubes however. The brands I see almost every day are HiWatt, Randall, Marshall, Ampeg, Markbass, older Fenders, Orange and an occasional Peavey metal amp and Carvin tube amps. I really do not see many smaller amps, if they are out there, the owners do not bring them to me. The rehearsal studios are large and mostly have older US and UK tube amps they buy for high prices in the US, used and ship them here. The average rehearsal studio has about 10 rooms, up to 21, and with each room having tube amps, a pa system and a few minimal effects. So they are good customers, 40-80 amps each, all living a hard life of rental room gear used 24 hours a day.

[Chuck H]

Indeed! It almost miffs me that we here on the forum go to such efforts to make good amps and these budget models that sell for crackers sound easily 90% (subjectively ) as good. Well... They're just amps after all. Not much new under the sun.

I didn't look up the schem but I doubt my diagnostics would have been as quick and accurate. Nice.

[silverfox]

Guitarded, Would be able to post the schematic for that amp? I've liked the sound of it but was never able to find the schematic for it. Haven't looked lately though.

Km6xz- I looked at buying one from Guitar Center but there was something just missing from the tone. The price was right. The tubes from the factory must have been the missing link.

Silverfox.

[Chuck H]

Since you're here on the forum I'll guess that you're at least a little into this stuff. I wouldn't buy a Bugera for a couple of reasons. One is that it feeds non domestic industry, not that my tiny efforts matter in that regard, but second... It's still a "budget" product. Good greasy kids stuff but not easy to service or modify. Just because it's got 90% of what tube amps are about doesn't mean it's reasonable to try and add the other 10% with modification. That last 10% comes from modest circuit modification that is highly impractical on that amp and, more importantly, the use of very high quality transformers, tubes and speakers. This last bit comes at a prohibitive price. If you're going to spend it you might just as well build from scratch or a kit. Or even buy into something suitable in the first place. That last 10% is the hardest to gain and the Bugera just isn't a good platform for that. It's great for what it is, don't get me wrong. It's designed for a purpose and it serves it well. If you honestly like the amp, buy one with the understanding that what you buy is what you get. and it won't be as durable or roadworthy from a service standpoint as a lot of other gear.

[Guitarded]

I've look all over my home PC. Must have got it on a work PC. Ill check on Monday.

[Guitarded]

http://music-electronics-forum.com/t32394/

Reply #4

[silverfox]

I wouldn't buy a Bugera for a couple of reasons

After close to two years of hanging on the Forums I can't imagine buying another tube amp for anything other than parts. With the exception of the custom, small shop builds the new amps are nearly all implementing unrepairable construction techiques- Some speculation here.

Mostly interested in the schematic. I'm somewhat of a collector, which is probably unique on this Forum... But I do study all the different approaches and I did like the sound. It just wasn't there.

I wonder how likely it is this Country will ever return to a onshore manufacturing base??

Silverfox.

[dmartn149]

[QUOTE

I wonder how likely it is this Country will ever return to a onshore manufacturing base??

Silverfox.[/QUOTE]

Manufacturing will be returning to the US, robots will be doing the work.

[J M Fahey]

Cool, if done, but not enough:
http://www.nytimes.com/2012/01/22/bu...anted=all&_r=0