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So I have this Bugera 1960 on the bench... When I first turned it on, it was loud as hell... I was scratching my head as to what the problem was... So I turned the amp off, then back on... BAM! it was half the volume... I turned it back off then on again, half volume... So I let it sit for a day... Came back and turned it on again and had full volume... Put the standby on, then switched the standby off and I had half volume.... It came in originally with a blown mains fuse and a bad tube... I replaced all 4 tubes with a matched quad and I've had zero problems with the power tubes... They all are on and have that nice blue glow inside... I have replaced the choke with a resistor, same thing... Full volume than half after I cycle the standby switch... Put the choke back in, same thing.... Replaced all preamp tubes with know good tubes.... Same problem.... Does it sound like maybe a cap? Coupling or otherwise? Maybe something in the phase invertor? Any replies would be most appreciated.... Thanks for looking...
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Is it the infinium or not?
Have you tried it with a patch cord connecting the FX send to FX return?Originally posted by Enzo
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I'd check all the solder joints on the tube sockets and elsewhere. If you bang on the amp while the problem is there, does it fix it?Comment
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It is not the infinium... I have tried jumping the effects loop... I have not tried banging it... I looked with a magnifier to find cold and cracked solder joints, to no avail... I just soldered every tube socket pin and will try it when I can... I'm at my day job atm....Comment
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SO when it is half volume, plug the guitar into the FX return. Still half?Education is what you're left with after you have forgotten what you have learned.Comment
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Guitar plugged into effects return = half volume as well...Comment
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Playing the Ohm Ranger I took a couple of measurements Power on, and standby in the play position...Power tubes... Heaters 24.7 volts DC, plate 457 Volts DC, screen grid 451 Volts DC, control grid ~-40 Volts dc...Comment
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Also, when I move the standby in to play position, it seems the signal sort of swells into being... My Bugera 333xl, as soon as the standby switch is moved, I have sound... This 1960, like I said, takes approximately 3 seconds for the sound to be there...Comment
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Have you checked voltages on the PI tube?Originally posted by Enzo
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Not yet... I will this evening... This week has been a crazy one...Comment
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Checking the voltages on the PI...
Pin 7 has ~22 VDC pin 2 has 21.07 VDC,
Pin 1 and pin 6 have 203 and 224 VDC respectively, pins 8 and 3 have 34 VDC on them... And pin 4 has -18.2 VDC and pin 5 has -6.46 VDC... Measurements respect to ground...Comment
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Anybody? LolComment
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Soooooo.... I just measured my output transformer primaries... Red (center tap) to brown: 6.5 Ohms... Center to blue:5.4 Ohms... Measured with tubes in....Comment
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With the power tubes out, 7 and 8 ohms on the primary... From brown to blue it reads about 11 ohms...Comment
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Whilst in half power fault mode, I would do some basic tests like check the bias current in each tube just see see if they are all making connection. Then I would check that each output tube grid is being driven - use a 1KHz sine wave signal generator on the input (or FX return), dummy load and scope or DVM on ACV with a 10nF 600V cap in series with one of the leads.Last edited by nickb; 01-27-2018, 11:37 PM.Experience is something you get, just after you really needed it.Comment
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