Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: matt mincer on June 02, 2018, 06:21:22 pm

Title: Bugera 333xl-212 Infinium schematic
Post by: matt mincer on June 02, 2018, 06:21:22 pm

Hey All,

I have a Bugera on my bench and can't find the schematic anywhere on the web. I find the non-Infinium schematic but not the one I have. I'm told the Infinium has an auto bias circuit for the output tubes if that helps. Anyone know where I could find the schematic?

Thanks
Matt

Title: Re: Bugera 333xl-212 Infinium schematic update
Post by: matt mincer on June 04, 2018, 06:53:22 pm

Thank you for contacting us. Per contract, all BUGERA schematics, as well as service manuals, can only be accessed by BUGERA authorized service centers. Therefore, we will not be able to provide you with the requested material. Please let me know if you have any further questions.

Title: Re: Bugera 333xl-212 Infinium schematic
Post by: John on June 05, 2018, 05:59:30 am

I had looked around too.
What makes the Infinium different than the XL?

Title: Re: Bugera 333xl-212 Infinium schematic
Post by: matt mincer on June 05, 2018, 07:14:13 am

Quote from: John on June 05, 2018, 05:59:30 am

I had looked around too.
What makes the Infinium different than the XL?

From what I was told on a Facebook forum, the Infinium uses an automatic bias control circuit on the output tubes. I think my problem is on the power amp board. It blows the plate B+ fuse as soon as the thing is powered up. It does it even if there are no tube installed.  The problem is that the circuit board is covered in black so it's difficult to trace out.

M

Title: Re: Bugera 333xl-212 Infinium schematic
Post by: John on June 05, 2018, 07:44:00 am

Quote

The problem is that the circuit board is covered in black

Ugh. Guess that explains the price.  :icon_biggrin:  They probably prefer you just swap out boards.


Do you have a current limiter? That would probably keep the fuse from blowing while you take voltages. If the tubes are out and the fuse blows, almost has to be a dead short. Maybe bad filter cap, something like that. I guess they're covered in epoxy too?

Title: Re: Bugera 333xl-212 Infinium schematic
Post by: matt mincer on June 05, 2018, 09:10:31 am

I've disconnected the B+ wire from the board and it doesn't blow the fuse. So I don't think it's the filter caps. Honestly, the amp board doesn't have much on it so it should be easy. Sadly, not so much so far.

Thanks
Matt

Title: Re: Bugera 333xl-212 Infinium schematic
Post by: GENOVA AMPLIFICADORES on February 12, 2025, 08:26:28 am

Hello everyone, I have a Bugera 333 INFINIUM, after a few minutes running on current, I have a limiter on the input to avoid blowing the fuse, the automatic bias attenuator indicates changing the output valves, if that doesn't work, they have been tested and they are ok, has anyone already had these with automatic bias?