Help with Blues Junior?

Discussion in 'Amp Tech Center' started by P Thought, Nov 25, 2019.

  1. P Thought

    P Thought Poster Extraordinaire Ad Free Member

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    Several years ago I gave my son one of my blueprint teles, and my Blues Junior along with it. He didn't play it much at first, but he's been learning to play the last couple years, mostly on acoustic but he's used the rig occasionally.

    The amp has developed a problem: when you turn it on it makes a loud, steady shrieking sound, no matter what you do with the volume. The sound continues until you turn the amp off, and it seems to be affected neither by any of the controls, nor by plugging in or unplugging the guitar. No sound comes through at all from the guitar. The guitar works OK on the dinky little Johnson practice amp I gave him at first, so I don't think it's the problem.

    My son is coming down for Thanksgiving. I asked him to bring the Blues Junior, and let me see if I can get it back in operation. I told him he could take one of my Peaveys back with him while I have his amp.

    I'll take it to a tech if I have to--probably have to travel for that--but are there things I can do myself by way of checking, or does someone who's experienced this have suggestions for which part might need changed? I have a multimeter, but I'll need some, er, coaching on how to use it. :oops:

    Thanks in advance. :)
     
  2. Pasta Player

    Pasta Player Tele-Meister Ad Free Member

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    Had similar problem here with a shrieking Blues Junior. 1st figured it might be tube related and switched some tubes around - no help. But they were very difficult to remove.

    Ordered some new tubes and then looked closely at the tube sockets themselves. Lightly touched them all with a soldering iron to reflow all solder, on all of their connections (even adding a little solder where I thought necessary). New EL84's went back in easily (as opposed to the older tubes) but figured that it was all probably the result of the tube sockets needing re-flowed and initially, due to the old EL84's tube pins being a bit corroded / oxidized.

    Once the old tubes had been in place for so long, me wiggling them to get 'em out probably added to the loose & poor connections.
     
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  3. fendrguitplayr

    fendrguitplayr Poster Extraordinaire

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  4. Zipslack

    Zipslack Tele-Meister

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    @Pasta Player is probably on the right track. Back when I did repair work, it was standard for me to re-flow all the PCB-mounted sockets with 60/40 solder. The ROHS stuff will crack pretty easily with vibration and heat. While you're at it, re-flow the connections for the input socket and possibly all the pots. The input for sure, the pots for future "insurance".

    Cracks too small to easily see with the naked eye can cause a lot of "strange sound" and intermittent issues.
     
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  5. corliss1

    corliss1 Friend of Leo's

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    I also am a believer in reflowing all the joints on the tube pcb board of the hot rod series amps. It takes seconds, and often cures problems before you realize you have them.

    Isolate - pull a preamp tube. Dude that stop the noise? Pull the next tube? If you pull the power tubes the noise will definitely stop, but that would at least narrow it down to if it's in the preamp or not. Other than pulling and replacing tubes, there isn't much I can recommend for a non-tech to do.
     
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  6. P Thought

    P Thought Poster Extraordinaire Ad Free Member

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    I misremembered the noise, either that or it morphed since the last time I heard it. It's more of a loud growl, no shriek to it.

    There are just two kinds of tubes, so I could do some testing if I bought a new one of each(?) The flash shows this up in the picture 'way better than it shows to the naked eye, but lookit the brown blurtch (sorry about the technical talk) around the resistor (ain't it) labeled R47, right below the left one of the three capacitors lying in a row. Would that be a good guess as to the suspect?


    Blues Junior r47.jpg
     
  7. corliss1

    corliss1 Friend of Leo's

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    Pull the power tubes. Measure the resistance of that guy, then measure the voltages. They might be a hair higher than what the schematic shows with the power tubes pulled, but they should be close enough. That'll get you more details most likely. Burnt resistors are usually a symptom of something pulling too much current through it, but they are rarely the problem itself.
     
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  8. P Thought

    P Thought Poster Extraordinaire Ad Free Member

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    I was going to go out to the garage and find my multi-tester, then take a picture of it and see if one of you here would show me which position to set the switch, where to put the pointers, and what to look for on which meter scale.

    Then I had images of discovering that the amp was toast, but that I could salvage many of its parts, strip its chassis, learn all about schematics, transformers, circuits, soldering, caps and resistors, tubes and bias. . .I'd use the chassis and the cabinet to make my own hand-wired amplifier, then I'd parlay what I'd learned into a lifelong fulfilling hobby, building tube amps for fun and profit. . . .

    All that ain't happening. I'd probably shock myself to death or burn down the place. I took the Blues Junior down to the music store, paid 'em the $35 inspection fee--applied to the bill if they do the work--and asked them for an estimate of parts and labor to repair it. If it's reasonable to repair it I'll have them do it, and if it's not I'll look for something (for my son) to replace it.

    You guys who know and understand these things have my deep admiration and respect. Thanks for the replies; I'm sorry to have troubled you.
     
  9. corliss1

    corliss1 Friend of Leo's

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    Probably the safest bet for sure :D
     
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  10. saltyseadog

    saltyseadog Tele-Meister

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    It is years since I applied the BillM mods to my made in USA green board BJr' but that R47 cap is one of the ones that he supplied along with the three others in a row. He said that the ones Fender put in were not very good and recommended replacing them all. One of the things he warned to look out for was that residue on the cap ends. Now BillM died a few years back but as far as I know there are others who have kept it going, either way you will find his recommendations for which make of caps to use as replacements. Here is a link to the BillM site which working or not is still the bible of advice for BJr' owners,
    http://billmaudio.com/wp/
     
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  11. Henry Mars

    Henry Mars Tele-Afflicted

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    Tube sockets with cold solder joints and tubes. With the JR look there first,
    I had a lot of crazy problems because of tube sockets. I re soldered them and the amp has been fine ever since. Also this thing will eat tubes especially if you play it cranked like I do. In my Jr they get replaced regularly when the amp is being used heavily ( every 6mo to a year.), Use quality tubes,
    The PS cap is crap ... replace it.
     
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  12. Tommyd55

    Tommyd55 Tele-Meister

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    That billmaudio site is gold.. Thanks for that link..
     
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