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Blues Junior Died..


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Hi guys.. My Blues Junior just decided not to work.. I played it this morning ok.. Then I turned it off and went out and when I came back to try to use it again, it didn't turn on..

When I turned the amp on, I could hear a very soft humming from what I'm thinking is the transformer but absolutely nothing else was working.. The humming's not from the speaker but from the back and the little on/off light's not coming on either.. I'm thinking it may be a blown tube but I'm really new to tube amps.. I did notice that one tube is a little bit blacker than the rest but not by much..

What's a blown tube look like?

I did opened up the back cover AFTER unplugging it and leaving it for a bit to hopefully get the caps to drain.. That got me a bit nervous.. Anyway, after poking around with a multimeter, I know that the 2 fuses inside the amp are ok and so is the fuse in the plug.. The switch also seems to be working.. Problem is that I don't know what the rest of the electronics do.. Any suggestions??

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here's the schematic from Mr Gearhead:

Blues Jr. Schematic

From what you've said, it could easily be a filament power supply problem, so you might want to check to see if the filaments are glowing ( remember, they're not very bright, just a tiny orange glow barely visible). That's just a wild guess, though, and shouldn't be considered a diagnosis.

Some other quick things to check (if you feel up to it):

  • Unplug it, carefully remove the chassis, and bleed the power supply caps (see the tutorial on this forum) - check for voltage across the caps before proceeding! Bleed caps again if necessary.
  • Check the board and wiring harness for any obvious disconnections, breaks or shorts.
  • Look for any signs of unusual heating (charring, warped plastic parts, etc.).
  • Check for leaky power supply caps - they should show an open circuit on your multimeter (after a momentary chargeup).
  • Pull all the tubes and check for broken pins, etc.
  • Finally, if you're feeling really froggy, reinstall the tubes, support the chassis on a pair of non-conductive stands (I use wooden blocks) so you have access to the inside, hook up the speaker, power it up, and carefully, using one hand only, check the voltages marked on the schematic.

As always, keep in mind that there's voltages in there that can kill you "Dedder 'n Hayull", to quote my redneck buds, so if you don't understand how to do any of this or don't feel comfortable with any of it, don't!. Be more careful than you think you need to be, and you won't have any sad stories to tell later (nor will your survivors). :D

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Nope.. Tried both the same cable and guitar on another amp and they both worked fine.. Like I mentioned, the on/off light isn't even on but there's a faint, barely audible hum from the back of the amp...


Sorry, LoveKraft, didn't see your post until I hit 'post' myself.. Thanks again for the suggestions, guys!! Will poke around in there a little more..

Edited by Stalefish
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