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Thread: Bugera 1960 half volume?

  1. #1
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    Bugera 1960 half volume?

    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...

  2. #2
    g1
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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?
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    Supporting Member mozz's Avatar
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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?
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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....

  5. #5
    Lifetime Member Enzo's Avatar
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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.

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    Guitar plugged into effects return = half volume as well...

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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...

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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...

  9. #9
    g1
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    Have you checked voltages on the PI tube?
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    Not yet... I will this evening... This week has been a crazy one...

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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...

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    Anybody? Lol

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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....

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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...

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    "Thermionic Apocalypse" -JT nickb's Avatar
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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; 01-28-2018 at 12:37 AM.
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    I haven't been able to get it in the full volume mode at all lately... Just half volume... All the tone controls seem to work... It is quiet... Just half volume...

  17. #17
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Danglin' Fury View Post
    I haven't been able to get it in the full volume mode at all lately... Just half volume... All the tone controls seem to work... It is quiet... Just half volume...
    That's good then. Have you ever tried to fix something that won't go wrong? Frustrating doesn't come close...
    Experience is something you get, just after you really needed it.

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    Yes sir I have... Lol! And you are correct... Frustrating doesn't touch it... Lol!

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    I have access to the 2 22nF coupling caps that are in the phase invertor... I'm going to change those tomorrow and see if that fixes the problem... The effects loop board seems to be ok... The jacks as well... When the amp came to me, the customer said the mains fuse blew and there was a dead power tube... I measured everything on the power board and it is ok.... As the power tubes are all operating as advertised...

  20. #20
    Lifetime Member Enzo's Avatar
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    Find those two caps on the board. Apply a steady signal to the amp. Now see if the signal is present on the phase inverter side of those caps, and then see if it is present on the power tube side of those caps. That will tell you if the caps are diminishing the signal

    I don't know what operating as advertised means. All glowing heaters? Did you check for B+ on the screen of every power tube? Pin 4.
    Education is what you're left with after you have forgotten what you have learned.

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    Yes sir... ~450 Volts DC on pin 4 of the power tubes....

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    Anything? Also earlier in the thread, I took some measurements of the output transformer... The primaries look a bottle low to me, anyone else?

  23. #23
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Danglin' Fury View Post
    Anything? Also earlier in the thread, I took some measurements of the output transformer... The primaries look a bottle low to me, anyone else?
    DC resistances don't tell you much. The best methods are probably (a) measure the primary inductance or (b) ring the transformer see RG Keen's method.

    Have you measured the grid drive yet?
    Experience is something you get, just after you really needed it.

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    I will do the lightbulb test, although its proving difficult to find a neon bulb locally... Here's the deal... I work at an electronics shop repairing and modifying high end analytical equipment for the battery test industry... Between that and my sons visiting every other day I have very limited time to work on amps, although I love doing it... Someday I hope to own my own shop but I digress... I just found out the shop I work in has a signal generator so tomorrow I'm gonna put in a 1kHz sine and see where the signal gets small... Man I'm telling you... The voltages in this amp and the resistance readings are all good... I've measured the resistance on all the caps (R.G. Keen says below 15 k ohms = bad caps) all readings are well above that...

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    Ok... Just applied a 1kHz sine wave into the Bugera.. Aaaaaaand it started red plating... Now its half volume AND the power tubes are red plating... Anything? Anyone?

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    Aaaaaaaand with the output transformer in the amp, still connected, I have about 237K ohms resistance between all taps of the primary measured to the secondary taps....

  27. #27
    g1
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    Does the red-plating only happen with signal?
    Do you have any other type of OT you can sub in there to test?
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    Quote Originally Posted by Danglin' Fury View Post
    Aaaaaaaand with the output transformer in the amp, still connected, I have about 237K ohms resistance between all taps of the primary measured to the secondary taps....
    Disconnect the negative feedback lead before measuring.

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    The red plating most definitely only happens with a signal present... I may have a friend that has a spare OT he can loan me... Im gonna see if the bias caps are leaking today around 11:00-11:30... So I Will be able to eliminate that... Perhaps I can get another OT this evening... If it is the OT, any place I can find one for under $125?

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    And thank you sir... I completely forgot to do that...

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    Not a terribly helpful reply, but my friend gave me a non-infinium 1960 that had bounced between all the techs in the northwest, who declared the amp had no fault, despite producing nearly no power and redplating the tubes. I had a poke around and all the voltages seemed sensible. I was going to test the OT with a neon but I instead have opted to pull all the PCBs out and build something else in it with a spare OT I have.

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    So did you try the other transformer to see if that was it?

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    Removed the feedback wire... Still have
    ~237k ohms between the primary and secondary...

  34. #34
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    It was the output transformer... Got one from eBay for $40... Worked perfectly... After reading several posts with extremely similar faults, and after troubleshooting everything else and finding no fault I deduced that it to be the output transformer...
    g1 and The Dude like this.

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    I also want to thank each and every one of you that helped me.... All of the knowledge here is worth so much... I appreciate all of you...
    nickb likes this.

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