Need Help Locating a Schematic

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by stebnera, Jan 23, 2008.


  1. stebnera

    stebnera Member

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    Anyone here have or know where to find a schematic for an Earth Sound Research "Earth Revival Model 1954?" I've also read that the company directly cloned Peaveys, so if someone knows the equivalent Peavey model that would be some help too.

    I volunteered to take a look at one for a friend. His story was the amp worked when he bought it. He took it to a shop when it quit working. They told him it had the wrong power tubes in it, and the output xfmr was probably fried as a result. They pulled the power tubes and advised against the cost of the repair vs cost of the amp, so he simply used the amp as a speaker cabinet (4 x 10 combo) for the past 4 years or so.

    When I opened the amp up, there are no tubes and it is also missing a fuse. One of the transformers is indeed a little "melty", but it's not connected to anything. Someone has significantly hacked this amp (messy, brown solder joints, wires cut, wires with stripped ends not connected to anything...) and I'm hoping to track down a schematic to figure out exactly what it's original condition is supposed to be. My guess is someone "modified" the amp to use EL34s or something, but I'm not sure how to figure out what tubes they modified it for as there are no tubes in it and my friend doesn't remember what the "wrong" tubes were. I know the original design was for 6L6s, and "schematic heaven" has schematics for some earth amps, but nothing that looks like this circuit.

    Any help would be appreciated.

    Aaron
     
  2. donnyjaguar

    donnyjaguar Member

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    It sounds like a piss-poor design. I think if I were going to create an amplifier Peavey would be the last manuf' I'd model mine after. You may be better off rebuilding it to a known good design making use of the working hardware in it.
     
  3. stebnera

    stebnera Member

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    Upon further investigation, I think the clipped wires are the ends of the output transformer. The brown solder joints are probably due to the output xfrm overheating, like the tech said he thought it had. It appears the tech did more than my friend thought he did when he diagnosed the amp having wrong tubes and the output xfmr being fried. I've begun making a schematic for the amp myself, but after making my way through 1/3 of the circuit or so, I feel fairly certain all that's happened is the guy cut the output xfrm leads and left the ends so someone would know where they were connected.

    This leads to my next question, how to determine what the output xfrmr is so I can replace it. I have pictures I can email anyone that thinks they might help identify it. It's a standard looking xfrmr, about 4" x 3.75" x 3.5" with 5 leads (grn, brn, blk, red, blu). The bolt pattern is 2-1/8 x 3-7/16. The number on the side is 200031. The insulation of the wires read "LL16217 CSA TYPE TEW 105 C." I'm equipped with oscope, signal generator, voltmeter and know how to use them, but I'm not sure how to test the xfrmr if I can't power it up to get impedance ratio or whatever other characteristics I would need to spec a new one if it can't be determined from numbers and photos. I've also never tested a xfrmr, so I'm not sure how to safely power it up if it's not wired into the circuit. It is definitely the output xfrmr. Any help would be appreciated.

    I understand the amp isn't the best, but the process of going through this is helping me make the conversion from mechanical engineer/lab technician to a hobbyist amp guy, so it's worth the time to me. My friend will also be happy to have the amp working again at relatively low cost, even if it is a relative POS.
     
  4. SatelliteAmps

    SatelliteAmps Member

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    You can contact Paul at Mercury Magnetics, and he can probably rewind the original for you, and provide a wiring diagram when it is done. www.mercurymagnetics.com
     
  5. stebnera

    stebnera Member

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  6. BassHog

    BassHog Member

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    I have the schematic for the 212 version of an Earth Revival combo. I'm guessing the version you have is similar right? 4 6L6 power tubes, solid state pre-amp etc?

    I also happen to have an output transformer that will work for this amp as well, it can use any generic 4x6L6 output transformer I'm pretty sure. I have tested this transformer in a Revival and it does work fine, it just didn't end up being a transformer problem so I still have the OT.

    Here is a link to the schematic.
    http://www.prowessamplifiers.com/schematics/images/Revival.jpg

    I got this from some amp tech in Sweden, it was close to unreadable but I went through it and cleaned it up as best I could. It was also wrong in a couple spots so I fixed it, the ground for the filter caps wasn't there for some reason.

    This is the only version of a Revival schematic I have ever seen.

    Good Luck
    Scott
     
  7. stebnera

    stebnera Member

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    that's the one! thanks again.
     
  8. DcinDc

    DcinDc Member

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    A GREAT BIG THANK YOU!!!!!! :thu:
     
  9. guitarcapo

    guitarcapo Senior Member

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    I think I see the problem from that schematic. The power tubes and speakers are on the wrong side of the amp.
     
  10. teemuk

    teemuk Member

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    Though its drawn rather confusingly that design is a direct clone of some Peavey amp, but I can't remember which model at this instant. Earth also cloned Fender amps and even several effect pedal and organ designs. Basically, everything that was moderately popular at those days.

    They were basically the American Behringer with the exception that while fire-catching Behringer amps are pretty much just an urban legend I've literally seen few Earth Sound Research amps catch in fire.
     
  11. DcinDc

    DcinDc Member

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    Well since the thread is rolling again....

    Did the OP ever fix the problem?

    Can anyone say with some certainty what impedance the stock speakers were?

    I've got a 4 6L6 version with the speakers in parallel for a 4 ohm load. Looks like maybe the speakers have been replaced.

    The problem is almost immediate red-plating. The cathode resistors are right, the screen resistors are good, the bias is good, the plate voltage is about 475-480.

    The static (idle) dissapation is about 30 watts a tube, so obviously the red-plating is real. It happens within a minute of turn on. This is with -60v of bias.

    GE tubes don't look nearly as bad as newer Chinese tubes.

    I'm thinking it must be the OPT, but I got to thinking if the speakers should be in series, rather than parallel, that my be throwing it that far off. Maybe not.

    Next step is to measure the OPT and determine if it is somehow mismatched or bad. Don't know any history of this amp.

    The screen voltage layout is wierd too. One tube of each pair having a resistor inline form the screen of the other.
    TIA
     

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