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Thread: 2004 Fender Blues Deluxe RI extremely weak and distorted

  1. #1
    Member Fred G.'s Avatar
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    2004 Fender Blues Deluxe RI extremely weak and distorted

    Hi All,

    I've taken on the task of repairing a friend's 2004 Blues Deluxe Reissue. It has an extremely quiet signal, with splatty, ugly distortion. The preamp volume has a minor effect on the volume, i.e., you can finally hear the amp when the channel volume gets to 7 or so; the remainder of the controls, including master volume, "seem" do nothing at all.

    I've mostly worked on P2P, eyelet board, and turret board amps with vintage style circuits, so this amp is a bit of a challenge to me, but I took it on to acquire new skills and learn something, so please bear with me.

    What I have tried so far, without any results, is:

    1. resoldered V1 pins, cleaned and retensioned V1 tube sockets;
    2. resoldered all the PI tube pins;
    3. tried jumpering the FX loop with a short cable.
    4. tested some of the component values (including the big 5W block resistors).

    I know there's a lot left to test. I just wanted to launch this new thread to ask questions and hopefully get them answered as I go along in this learning process. The circuit board and solid state components are a whole new ballgame and I'm taking it slow.

    What are the suggestions as to where I go from here?

    I'm planning on testing the PI plate resistors and looking further at those 5W resistors, and when the magnifying glasses I ordered get here, inspecting the solder joints.

    Thanks in advance,

    Fred G.

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    Last edited by Fred G.; 11-15-2019 at 08:41 PM.

  2. #2
    Lifetime Member Enzo's Avatar
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    MAke sure the speaker is plugged into the MAIN speaker jack, not the extension speaker jack. The MAIN jack is the one with the shorting contact across it. The shunt opens when a plug goes in, but if you use the extension jack, the shunt remains.

    Testing plate resistors couldn't be simpler. Go to pins 1 and 6 of the 12AX7 tubes. If there is B+ there, the resistors are not open.

    You have resoldered the small tube sockets, but the power tube sockets are the ones that crack their solder most.

    Circuits are circuits, so it doesn't really matter what the parts are on, turrets, eyelets, terminal strips, pc boards.

    Use the FX loop to test. Plug the guitar into the FX return. Is the output strong or still real weak? And plug into the regular input jack and connect the FX send to some other amp. This tests your preamp. Does your preamp sound OK coming out that other amp? We just determined if the problem was preamp or power amp.

    I use my eyes for a quick check, but if I suspect a solder joint, I just resolder it. Why waste time trying to see a crack that may never be visible? My iron is already hot, and resoldering a tube socket takes literally just a few seconds, lots faster than me and my hand lens.

    In fact that whole Fender Hot Rod series and their other amps made the same way, like yours, I just automatically resolder the power tube socket pins.

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  3. #3
    Member Fred G.'s Avatar
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    Well...I've already tested the plate pins on all tubes, and the voltages seemed normal enough (around 240+ VDC in the preamp and PI tubes, 400+ VDC on the power tubes - I don't remember the exact values. But it was among the first things I tested).

    Already made sure the speaker was plugged in the correct jack (but still may clean them).

    I've plugged a guitar into the power amp in jack - silence. I'll try it again, though.

    I haven't tried plugging the preamp output into another amp yet. I don't have any other amps with FX loops, so it'll have to go into a regular input jack. I'm a little suspicious of those two jacks - maybe they're corroded?

    Maybe it's just me, but I find it a hell of a lot more of a PITA tracing circuit paths on a PCB than I do something more primitive...adding in the unfamiliar solid state components makes it more daunting.

    Pressing forward! Thanks for your help - I'll be back after I get some free time to dig a little more later this weekend!

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    Supporting Member Randall's Avatar
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    Did you test the amp with another speaker? I have a Twin Reverb in my shop that came in with very low output. BOTH speakers measured ~8 ohms, but were frozen up solid.

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    It's weird, because it WAS working fine.....

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    Supporting Member The Dude's Avatar
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    Check voltage at output tubes screen grids. You could have open screen resistor(s).

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    Lifetime Member Enzo's Avatar
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    The loop jacks are PROBABLY OK, you already patched them together. I suggested using them simply because they are at the mid point in the amp circuit. Divide and conquer.

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    Education is what you're left with after you have forgotten what you have learned.

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    i would check out the dual supply for the opamps,especially on U1,that is notorious for problems in all the budget Fender amps like the hotrod,and wiggle all the flat cables connecting the boards,it could be just some bad soldering.

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  8. #8
    Member Fred G.'s Avatar
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    Fixed!

    It was the two 5W resistors. Their solder joints had gone cold.

    Thanks everyone, for your help!

    Fred G.

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