Blues Jr. hums w/ no input/volume @ 0 and sounds distorted when played at any volume

Discussion in 'Amp Tech Center' started by Quinn T Eskimo, Oct 17, 2020 at 2:33 PM.

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  1. Quinn T Eskimo

    Quinn T Eskimo NEW MEMBER!

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    BJ III blew fuse
    1. Replaced fuse, noticed crackling in power tube. Replaced power tubes. Now amp has crackling sound when played. Also humming sound at any volume and even with no input. Also resoldered all tube bases.

    2. Replaced preamp tubes. Problem unchanged.

    3. Replaced 4 large IC capacitors. Problem remains unchanged.

    4. Poking around board/tubes with chopstick has no affect.

    anyone have any other suggestions?

     
  2. JRapp

    JRapp Tele-Meister

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    1. remove Fender name plate with hydraulic jack
    2. discard amp in dumpster
    3. slide a real amp (not designed by Shane Nicholas) under the name plate
     
    Last edited: Oct 17, 2020 at 3:47 PM
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  3. edvard

    edvard Tele-Afflicted

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    If it blew a fuse, assume something shorted. Pull the tubes and check to make sure you are getting proper B+ and Heater voltages, as the transformer may have gone. Check for AC at the Plate connections, which might indicate your rectifier stage went kablooey; inspect diodes and power caps.

    Beyond that, I dunno.
     
  4. Jon Snell

    Jon Snell Tele-Holic

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    It would be useful to know if the hum is mains frequency or double mains frequency. That will at least tell us where the hum comes from.
    Check the screen grid resistors, replace R52 with 33k.
     
  5. Quinn T Eskimo

    Quinn T Eskimo NEW MEMBER!

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    Thanks for the replies. Based on my ability to try these recommendations (I’m basically a residential electrician with a multi-meter and soldering gun), I may have to have an amp tech look at this.

    I’m good at following directions if anyone can offer anything more specific (i.e. meter across these two points).

    Thank you
     
  6. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    For the hum. You have the amp apart. Make sure the grounds are attached to the chassis. The output jack doesn't appear to be grounded, for instance.

    Crackling:
    Make sure tubes pins/sockets are making good contact. Use deoxit and work tube in/out of socket.
    You have already re-flowed the solder on the socket terminals.
     
  7. 4wotitswurth

    4wotitswurth TDPRI Member

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    I had a similar problem with mine. I’m not saying this is necessarily the case with yours, but after cleaning tube sockets and replacing tubes etc I finally swapped the tube board with this..

    https://reverb.com/item/10803881-fe...acement-tube-pcb-with-bias-test-points-by-mox

    might be a different version for your BJ3, but at least for me it solved all my problems. Basically the tracks on my tube board had burnt across with excess heat, my guess... like you, a guy with a fluke and a weller.... ;)
     
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  8. saltyseadog

    saltyseadog Tele-Meister

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    Earlier this year I did a major mod to my green board BJr' adding one of these boards along with a new Hammond 1760F output transformer which made a huge difference to my amp. Over the years I had it twice into a tech with problems with the original tube board overheating and damaging connections. These boards are made differently and are much better than the Fender ones and a very helpful seller as well. Cannot talk any higher about these. Unsure whether this will fix the OP's amp but any BJr' owner should be aware of this simple to install mod.
     
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