Trouble with my 5E3 clone

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Mike_E_McGee, Jan 9, 2005.


  1. Mike_E_McGee

    Mike_E_McGee Member

    Messages:
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    Dec 30, 2004
    Well, I've almost finished my 5E3 clone. I thought it was done, fired it up, and got nothing. It turns out that I had miswired the rectifier tube. OOPS! I rewired, and the normal channel sounds great! I'm getting nothing out of the bright channel though. I've looked and looked, and can't see anything wrong. The tone control functions on the normal channel. If I crank the normal volume with nothing plugged in, I get loud hiss (to be expected). Doing the same on the bright channel gets me a tiny hiss when almost completely maxed. I've posted on the 5E3 forum, but have yet to get any responses (about the bright channel, they were very quick to respond to my recto problem). This is a mission amps kit, and I'd appreciate any ideas on where to trouble shoot.
    Thanks,
    Mike
     
  2. glasman

    glasman Guest

    Given the fact that the normal channel is working that leaves a pretty small area to trouble shoot.

    That design has 1/2 12AY7 (12AX7) for the preamp. Check your
    voltages between the Normal and the Bright Channels. The Cathodes are tied together based on this schematic.

    https://schematicheavencom.secure.powweb.com/fenderamps/deluxe_5e3_schem.pdf

    Pin 3 and 8 should be tied together according the original fender prints. So measure the voltage to ground from pin 3 or 8.

    Then measure the voltage between Pin 2 and 3, should be close to the same voltage as you measure above. Then measure pin 7 to 8, once again, should be close to what you measured above. If not check the input jack wiring around the 1meg ohm resistors.
    Make sure that the grid is not tied to ground somehow.

    Next thing to check is the voltage on pins 1 and 6 of the preamp tube to ground. They should be identical. Both are fed from the same supply through 100K resistors.

    If all is ok up to this point, check the Volume control wiring for the bright channel.

    There is not much more than this, if all else fails, give Bruce at Mission a call.

    Gary
     
  3. Mike_E_McGee

    Mike_E_McGee Member

    Messages:
    136
    Joined:
    Dec 30, 2004
    Thanks for the help!
    Here are the measurements I got:
    Pin 3 to Ground is 13.6mV
    Pin 8 to Ground is 13.6mV
    Pin 2 to 3 is 312mV
    Pin 7 to 8 is 284mV
    Pin 1 to 7 is 1.6V
    Pin 6 to 7 is 1.6V
    The Grids (pins 2 and 7) are not grounded.

    If I read what you said correctly, pins 2>3, and 7>8 are a bit off from each other, and both are off from the pin 3 to ground/pin8 to ground.
    Since the normal channel works, I'm guessing that the pin 7 to 8 connection is indicative of the problem, but I'm still not sure where to go from here.
    If you could give me my next step as well, I'll be eternally grateful!
     
  4. glasman

    glasman Guest

    This seems low to me, you should see around 1 to 1.4volts (this is a guess) between the cathode and ground.

    The voltmeter was set to DC?


    Before I ask anymore questions, what type if tube is the amp using for a preamp?

    If it is a 12AX7, then Pin 1 to Ground should be in the order of 100 to 200 volts, depends on the power supply.

    Pin 6 to Ground should also be in the order of 100 to 200 volts.

    Lets start here.....

    Gary
     
  5. Mike_E_McGee

    Mike_E_McGee Member

    Messages:
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    Dec 30, 2004
    Once again, I expose my ignorance...
    Here are the voltages with a speaker connected, and the standby off:
    Pin 3 to Ground is 1.83V
    Pin 8 to Ground is 1.83V
    Pin 2 to 3 is 1.83V
    Pin 7 to 8 is 1.83V
    Pin 1 to 7 is 113.2V
    Pin 6 to 7 is 117.7V

    It is a 12ay7.
    Obviously I'm a bit ignorant of the workings of the amp. I know I'm close to getting it, and I'm learning a lot, but I've clearly bitten off more than I can chew. Thanks again for the help!
     
  6. Mike_E_McGee

    Mike_E_McGee Member

    Messages:
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    Dec 30, 2004
    By jove, it works!!!!!!
    I haven't done anything though. I must have fixed it by staring at it intently for most of the day?!?
    I don't get it, but I'm going to play with it for a while.
    Thanks again!
     
  7. glasman

    glasman Guest

    If has started working after poking around in the amp, you may have a cold solder joint. You might want to use your soldering iron to reflow connections on the first tube section.

    Have fun with the amp.

    Gary
     

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