5E7 Checkout

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jbever, Apr 30, 2008.

  1. jbever

    jbever Member

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    Interested in input on the following:

    5E7 seems to be very treblely and harsh. By the time I get the treble up around 7 to get some overdrive it gets real stiff and harsh. I'm using a strat into the normal input. 5u4G EH rectifier w/ 6L6 SED's. 12AY7 in V1.

    In checking voltages everything is within tolerance except:

    Plate voltages on V1a V1b and v2a are high even considering the +/- 20%. They're coming in at about 200V. Schem is 140.

    Cathode on V1a V1b v2A are a little low at about 1.6v. Schem is 2.2.

    Another thing I've never seen before on the rectifier are resistor / diodes bridging from pins 3 & 7 on the AC side to pins 4 & 6 respectively.

    B+ Supply is 432v coming of Pin 8 of the rectifier.

    Questions are:
    What are the bridged resistors on the rectifier? Surge protection?

    Are the V1 & V2 voltages ok?

    I've always heard that the 5E7 is the supreme amp and right now I'm not that impressed. My reference is my 5E3 Mission build, great amp!

    Any help is appreciated, thanks.
    Jerry
     
  2. Trout

    Trout Member

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    I suspect the diodes on the rectifier are to prevent arcing internally in the rectifier tube.

    If you use a glitch capturing storage scope, it will show some serious transients generated form the collapsing magnetic field in the power transformer. It is transformer dependent, and spikes of over 3KV have been seen on some transformers. The avalanche rated diodes allow most of the transient to be dissipated before becoming a lightning bolt inside the 5U4.

    This tends to show up commonly when entering and leaving standby mode.

    Here is the Diode Data for the ones used in the Fender 5E3, BYD33V data sheet , I suspect those are the same or similar and used for the same reasons.


    Tubes play a big role in the 5E7, I have found that most new product tubes tend to be extremely crisp. If you can get your hands on an NOS RCA 12AY7 it will clear up some of that.
    I have tried the 12AY7 in both V1 and V2 positions and it also helped.
     
  3. tlpruitt

    tlpruitt Member

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    Is it a 5E7 clone or an original?

    If you are using the original Fender schematic I wouldn't be too concerned with the slightly higher voltages you are seeing. That is pretty typical.

    I don't usually run the treble that high with mine. I usually have the treble between 3 and 5 (on a scale of 0-12) when I use the normal channel. Treble on 7 would be very bright on mine.

    The easy approach is try swapping some preamp tubes. Don't overlook the V3 tube. Half of V3 is used for the phase inverter but the other half is used for the last gain stage before the phase inverter so if V3 is a bright tube the amp is going to be bright. I had an EH 12AX7 in V3 and replacing it with a smoother 12AX7 definitely tamed the high end a bit for me.

    Also, you may know this but if you want more gain you can use a slightly hotter tube in V1. I am torn between a 12AY7 and a 5751 in V1 on mine, with the 5751 having a little more gain.
     
  4. jbever

    jbever Member

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    Thanks for the feedback guys. The amp is a Victoria. Good info on the rectifier. I may just have a false expectation of how high I can run the treble. I probably just need to back down and keep looking for the right tube combination. I just wanted to make sure the voltages were ok so that I wasn't chasing my tail. Thanks
    Jerry
     
  5. redtoploader

    redtoploader Member

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    You may want to go with a higher gain tube in v1 and turn the treble down.

    Does the amp have new jensen reissues? These might take awhile to break in...never liked those myself, but some people do.
     
  6. 909one

    909one Member

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    I just got a ceriatone 5e7 clone and besides some noise issues I was having with the amp, its a pretty cool amp.

    With my Tele in the normal channel I usually have the treble and bass both set around 7. Its not too bright for me. In fact, the higher the volume is, the more saturated it gets, and I find that I need that level of treble to keep the amp cutting through the mix.

    It's a cool amp, but not right for all situations IMO.
     
  7. tommytomcat

    tommytomcat Member

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    The voltages are going to be higher because most of us are getting 120-130v AC from the wall.. When the 5e7 came out it was only 110v AC.

    Yours may be bright and harsh right now because in part the speakers aren't broken in.. Even Alnico's need some break in time.

    I've built 2 5e7 kits.. both great sounding amps once I figured out what preamp tubes sound best with them. One has v1=5751, v2-3, 12AT7's.. The other I ended up with v1=12AV7 (really close to a 12ay7 in gain factor) and V2-3=12AT7's. There was just too much grit/not enough definition when I use a 12AX7 in any of the 3 positions. Also, on the bright channel, check the bright cap on the volume control. Schemo has a 100pF cap in there. You can lower it to a 47uF cap to try and tame the highs some. Or jumper the channels and use both volumes to find a blend that you like.
     

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