Home › Forums › Help/Technical Questions › My 12AY7 Pre has died

Viewing 11 posts - 1 through 11 (of 11 total)
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  • February 9, 2011 at 11:51 pm #81337
    realgarry
    Member

    Went to record a voice-over the other day and it wasn’t working. Tubes are lit although I don’t know if that means a tube still could have gone bad (I tried some other tubes with no luck also). I’m not sure if I should spend the money to send it in and get it fixed. It’s always been noisy (hiss-like noise, not ground loop noise) and if I thought I’d get the unit back in working order, and with lower noise, I’d do it. Anyone else with a similar experience?

    February 10, 2011 at 12:08 am #114214
    ranjam
    Member

    That’s gotta suck. Can you measure any Plate voltage? I realize that may be over most people, but if you can, you might find a missing voltage. The real bummer is that if the voltages seem to be there, you could really be in trouble. Well, if the Plate voltages aren’t there, you’re still in trouble. No schematic, no easy way to trace it out, and who knows what the solid state devices are. Ouch.

    February 10, 2011 at 5:41 pm #114227
    realgarry
    Member
    Quote:
    That’s gotta suck. Can you measure any Plate voltage? I realize that may be over most people, but if you can, you might find a missing voltage. The real bummer is that if the voltages seem to be there, you could really be in trouble. Well, if the Plate voltages aren’t there, you’re still in trouble. No schematic, no easy way to trace it out, and who knows what the solid state devices are. Ouch.

    Yeah, measuring plate voltage is over my head, but I think you’re right in that I’m screwed. I guess I was hoping EHX would just jump in, say they’re sorry I got a bum unit and send me a new one. A quieter one. For my VO work I always had to use a noise gate after the 12AY7 pre. My previous tech support queries whet unanswered.

    February 10, 2011 at 11:32 pm #114231
    SanquiFlerb
    Member

    This forum is for discussion between ehx users. If you want to get your unit repaired contact them https://www.ehx.com/about/contact . Good luck with it!

    February 10, 2011 at 11:38 pm #114232
    realgarry
    Member
    Quote:
    This forum is for discussion between ehx users. If you want to get your unit repaired contact them https://www.ehx.com/about/contact . Good luck with it!

    Yes, and I, as the owner of a 12AY7 pre, am discussing it. Thanks for “checking in!”

    February 10, 2011 at 11:42 pm #114233
    ranjam
    Member

    This http://www.untrue.ch/test/ehx_12ay7/ehx12ay7.html is as close as I can find to any type of photo representation of what is inside. You can see the two transistors on the shared heat sink in the top toward the right hand side of the first photo. Plus an IC in the upper left. Who know what EH uses; if they have a house number or a real world number. If you had the right test equipment you could find out what was wrong, or a schematic could let you signal trace it.
    If the IC has a real number on it, Google the pin out, and ‘scope the input and output pins if you had a signal generator.
    It almost looks like a plain TLO74. Wow. I wouldn’t expect such openness from EHX, but this is a pleasant surprise if it is true. Here http://circuitdiagram-schematic.com/12/pre-amp-equalizer-using-tl074/ is a preamp schematic (NOT the EHX, but just one using the TLO74) to get the pin out and an idea of a typical circuit.
    That’s all I know. With real part numbers, you can test anything, and know where else to look. I have had this happen before, and just plain dumb luck helped me. And this was with supposed name brands that had a ‘reputation’. If you have nothing to lose, go for it!

    February 10, 2011 at 11:46 pm #114234
    realgarry
    Member
    Quote:
    This http://www.untrue.ch/test/ehx_12ay7/ehx12ay7.html is as close as I can find to any type of photo representation of what is inside. You can see the two transistors on the shared heat sink in the top toward the right hand side of the first photo. Plus an IC in the upper left. Who know what EH uses; if they have a house number or a real world number. If you had the right test equipment you could find out what was wrong, or a schematic could let you signal trace it.
    If the IC has a real number on it, Google the pin out, and ‘scope the input and output pins if you had a signal generator.
    It almost looks like a plain TLO74. Wow. I wouldn’t expect such openness from EHX, but this is a pleasant surprise if it is true. Here http://circuitdiagram-schematic.com/12/pre-amp-equalizer-using-tl074/ is a preamp schematic (NOT the EHX, but just one using the TLO74) to get the pin out and an idea of a typical circuit.
    That’s all I know. With real part numbers, you can test anything, and know where else to look. I have had this happen before, and just plain dumb luck helped me. And this was with supposed name brands that had a ‘reputation’. If you have nothing to lose, go for it!

    Thanks RanJam!

    February 12, 2011 at 6:50 pm #114253
    Jazzman57
    Member

    Mine didnt die yet, but it has the same constant hiss, does any one know what tube goes into which slot Im thinking maybe the tubes are reversed causing the hiss?

    February 12, 2011 at 8:35 pm #114254
    ranjam
    Member

    You can’t reverse the tubes. A 12AY7 is a 12AY7, and they only go in one way. You might just have noisy tubes. I’d try any other ‘similar’ tube and see if the noise improves. If the low gain was appealing, stick with low gain tubes. Try a 5751. If you have time and money, hunt down NOS 6072’s. If you have an old TV shop around your corner, ask about any 12AD7, 12DF7, 12DM7, 12DT7, or 12DW7’s they have. Anything will work in theory, but if the gain is too much the distortion might not be very pleasing. It won’t hurt to experiment, though. That’s how you learn.

    February 13, 2011 at 1:10 am #114255
    SanquiFlerb
    Member
    Quote:
    Yeah, measuring plate voltage is over my head, but I think you’re right in that I’m screwed. I guess I was hoping EHX would just jump in, say they’re sorry I got a bum unit and send me a new one. A quieter one. For my VO work I always had to use a noise gate after the 12AY7 pre. My previous tech support queries whet unanswered.

    I came here to tell you about the contact info because since this is the official ehx forum people thinks that ehx staff pops up every day and reads posts, which is not the case even if it should be that way. ehx staff rarely posts here unfortunately, because it would be nice to get official support on line.

    February 13, 2011 at 3:13 am #114262
    Jazzman57
    Member

    Thanks for the information and the suggestions on the tubes, as you can tell Im not familiar with tubes at all. I saw the two different numbers and thought… Well there I go thinking again LOL

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