Bugera joke?

[drewl]

Did you hear about the guy who bought a Bugera?

But seriously folks,
Got an Infinium 6262 here I'm retubing.
It's stenciled that it can run 6L6's or EL34's, but there's no switch or bias adjustment pot as shown on the schematic for it.

This one has four tube monitoring LED's on the back, what'd they do change the design?
This thing looks pretty new.

[Enzo]

There is not a slide switch under a cover on the rear panel?

[Jazz P Bass]

The tubes are automatically biased.
This guy in the video is a real gorp but he spells it out (kinda)
BUGERA INFINIUM Valve Life Multiplier Technology - YouTube

[Enzo]

Well, at least it lets me know they came out with a new line. Amazingly free of real information though. I like the part about proper biasing will make your power tubes last 20 years. Hell, if you never bend your strings, they will last 20 years too. Neither one will have anay life to the sound, but last, they will.

I gotta go find the schematic now and check it out.

WOW, big departure for Behringer. The service manaual; is 14MB, has all the schematics AND mechanicals.

Each tube has a sensing resistor in the cathode leg, which sampled voltage is sent to the autobias board. There each tube current is input to a small processor IC, and it controls the bias for that tube, using op amps and transistors. It works or it does't I guess. There doesn;t appear to be any adjusting available. And just what it decides is proper current is hard to say. I guess you could measure that easy enough.

[drewl]

Yeah, the rear panel LED's are connected to that "auto-bias" board.
I was going to to look up the chips but I'm kinda' busy this week.

The bias circuit was holding at about 33ma per tube, around 60% dissipation.

[Jazz P Bass]

I can hear it now.
"I want to make my autobias board adjustable.
Where do I put a pot?"

[drewl]

Well that video posted was 10:55 of Gorp I'll never get back.
Didn't explain anything technical.
This amp had a bad 6L6 which lost it's vacuum and blew the mains fuse, the "Infinium Valve life multiplier" circuit did nothing to prevent the fuse from blowing!

Nice idea with the auto-biasing, but looking at the board you'd think they would have used some better and bigger components, it's mostly all surface mount stuff, although with the schem Enzo can see if the parts are spec'd right.

[Enzo]

I dunno. COnsidering it is the bias for a tube, there will be next to no current flowing, so parts need not be beefy. Voltage will be under 100, so no special high voltage parts are needed either. The sensing cathode resistor was a 4.7 ohm if I recall. (I don't have the file open at the moment) So at 33ma, it dissipates about 1/6 of a watt. So even at twice the current we are still under a half watt.

[drewl]

That sounds about right as I was reading almost 5 ohms from the cathode to ground.
I had pulled two tubes and the bias voltage on the empty sockets was like -30 something, while on the tubes still in it was around -50.
That's when I realized the board was compensating and adjusting the bias voltage.

I guess we'll see if the circuit functions well over time, or if we start seeing failures from it in the future.

[Gtr_tech]

Heh....ok. Let's be smartass and see how it deals with JJ 6V6s. I'm DYIN' ta know....

[Mr Johnny Birchwood]

on the bugger-uh subject, i ended up with a model 1960 on the bench a few days ago. It's pretty impressive that some pencil-pusher designed an amp so cheap and shitty that actually works(depends on your definition of 'works'). I'm not a factory authorized tech so Behringer wouldn't release a schematic. Owner reported weak grainy distortion. Tried a new set of JJ EL34s and biased em to -38g1. Plate and g2 vdc was 460-470 ish. Still weak and grainy, volume pot was scratchy indicating bad coupling cap on v1, but the black enamel crap on the board prevented me from a proper visual inspection of the circuit. The connectors from power supply or choke or something kept breaking contact and cutting B+ voltage. Didn't really feel like taking the time to hard wire the crappy steel coated tfx leads to the pcb. I had this thing on the bench for an hour reversing a previous amateur repair attempt so that I could properly diagnose and just gave up and told the thing's poor owner to take it back to toys r us and buy a real amp, or for a few hundred bucks I could build a PTP 50w 2xel34 using existing chassis and transformers. My seat of the pants calculation tells me that the reduced current demand on the tfx plus half-current through the opt combined with the higher impedance reflected to one pair of tubes vs 2 pairs would yied a pretty dynamic 50 watt amp with some headroom and better mid and low frequency opt coupling. Are these transformers even worth salvaging? Shiny chrome bellhousings notwithstanding, they seem like extremely cheap components.

[Gtr_tech]

You get what you pay for....

[drewl]

This amp actually sounds pretty good.
It's their ripoff of a 5150,(you seen their "Trirec- gee what's that stolen from?-) and sounds better than some of those I've played.
This looks like the future of amp mfg. Seperate boards with small/surface mount components tied together with cheap connectors like a computer. Have you guys seen some of the new "mini" amps...more fun to work on!

[Mr Johnny Birchwood]

Bugger-uh's do not sound good. Marshall's sound good. Fender's sound good. This thing sounds like what it is. A cheap-o tube amp. A real output transformer might punch it up a bit, but why bother? Not to say that there aren't some half-decent quality amps comin' from chiney-land these days, but I'm not ready to drink the cheap chinese kool-aid just yet. Luckily there are still some old school rock and blues dudes out there with some real amps that want them serviced. I won't put another one of these POS up on the bench ever again. Not even to replace an input jack. In 20 years there will be hardly anybody left that remembers what a real amp sounds like or even cares. This bugger-uh is the worst of the worst. I could build a 'honest 50w' pp amp with the parts in my junk bin that would eat this thing for breakfast and crap cheap pcb mount tube sockets. Ok, rant over, have a nice day!

[Jazz P Bass]

Gotta love em for that 'black' pcb.
Try tracing one out, you'll love it.