Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joelap on May 02, 2010, 10:58:07 am
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Hi, I've got a Bugera 6262 on the bench right now. Its a local guy's amp I told him I'd take a look at before he gets in too deep. Powers on but no sounds comes out. I was able to diagnose it down further but looking for any potential obvious issues I may not be thinking of. There is NO sound whatsoever coming out, not even an audible hiss when the master volume is cranked. I am using verified working speaker cab, speaker cable. Power tubes aren't lighting up at all (and no heat coming off them either, so its not like the heaters are just not visible), but the preamp tubes ARE lighting up. The amp has a "preamp out" jack and I ran that into my poweramp and sound definitely comes out but the distortion channel is markedly quieter than the clean channel. My initial thoughts were blown OT before I got too far into it, but if the power tubes arent getting current at all and the preamp tubes are, then the problem I'm thinking is a connector to the power tube circuit board or the board itself. However, this still doesn't address the issue of the lead channel being much quieter than the clean channel. No connectors are visibly loose and no components are visibly "blown", and amp doesn't have the "blue smoke smell". We know these Bugera's are budget clones of other amps, this one being a budget clone of a Peavey 5150 (imagine that, a budget clone of a Peavey). Serial number build date states March 2008. Here were are, maybe 2 years later and the thing is crapped. All tubes are brand spankin' new as well. Feel bad for this guy really ... dropped $600 for the amp and at least $125 on a new complete set of pre and power tubes. He coulda bought a damn good condition 5150 used on ebay for about what he paid for the Bugera.
At this point because of the circuit board nature and the lack of tech support I am expecting from Bugera (or just rediciously high cost for a replacement board), I suggested he sell it for parts, or gut the chassis and enclosure and try and sell that to someone who builds / tinkers with amps.
Any other things I should check into before making that recommendation? Any other ideas what could be the issue?
Thanks,
Joe
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> the thing is crapped.
I see two, or maybe one, problem. Likely a $1 repair (though it may take all morning to reveal it).
Being a PV-copy, it is very likely the preamps are heated with DC and the big bottles on AC.
The basics:
AC Voltage at power transformer secondaries.
DC voltages at main power filter caps.
AC voltage -across- power bottles' heater pins.
You expect 400V-500VDC at the first high-voltage large filter cap, descending to 300V to feed preamps, maybe a lower voltage for a mondo-grind stage.
You expect 6.3VAC across power tube heater pins. If it isn't there, but you find 6.8VAC across the fattest PT leads, trace it out. There's a bad connector, a blown fuse, a bad solder joint (fat connector pins on thin PCB make bad solder joints), or a vaporized PCB trace. If not obvious, pull the big tubes (maybe including the driver) and ohm-meter your way from PT heater leads to tube pins.
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Power tubes aren't lighting up at all (and no heat coming off them either, so its not like the heaters are just not visible),
Divide and conquer. You may have multiple problems but no power tube filaments is a show stopper. Concentrate on fixing that. Dead filaments is an easy fix on paper, but may be much more involved inside a modern amp.
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Check out all cable connectors. IIRC there should be also a filament wires in some of those connectors. That is (or has been) a common failure point in bugera amps.
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Thanks. By "crapped" I didn't mean it was beyond repair. I meant less than 2 years since the manufacture date and there's an issue, on an amp thats barely been gigged.
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Just had a Bugera in the shop.The one I had used a filament fuse inside the chassis.Check for hidden fuses.Fuses inside the chassis are common on lots of new production amps.Silly I say,but who am I to stand in the way of progress?
And always check to see if it uses DC heaters.I recently had a Marshall TSL401 that had DC heaters on the preamps and AC on the power tubes and phase inverter.
In your case it may be the 1 dollar fix as PRR indicated.Lets hope so for your friend's sake.
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I just finished Bugera 1990 , it had some of the same symptoms, if the power tubes aren't heating up you have no heater voltage, pull the tubes and check for voltages , trace it back , there's a resistor on the power tubes pcb , most likely it's fried. on the preamp brother good luck the 1990 is surface mount technology , and I bet this one is too your best bet is to order a new board . I emailed Bugera and the engineer there was very helpful . Good Luck Brother