I Think I Fried My Homebuilt 5E3!

Discussion in 'Shock Brother's DIY Amps' started by JCMNelson, Jul 4, 2009.

  1. JCMNelson

    JCMNelson TDPRI Member

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    So, I was tying out some tube variations using 12AX7's, 12AY7's, 12AU7's and a 6JE8 that I had lying around and everything was going great.

    Switched off the amp, put a 12AU7 in both V1 and V2, switched it on - and, nothing! Switched it off again and tried numerous different combinations but got absolutely nothing out of it!

    The lamp comes on, the valves heat up, but there's absolutely no sound at all! Tried different cables, with and without guitar, but nothing, apart from a pop when the amp is switched off (everytime)!

    I haven't opened it up to check anything yet, anyone got any ideas?
     
  2. muchxs

    muchxs Doctor of Teleocity

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    Aw, rats. If you're getting a pop we can rule out the speaker. Still, check it with a known good speaker.

    Swap tubes with known good tubes.

    Tube swapping results in no sound. Are you sure the last tubes you put in there are fully seated? Did you damage a socket?

    Make sure your 6V6s are fully seated and properly oriented. If you have a broken center pin you can stick them in bass-ackwards. There's are Chinese sockets in circulation with oversized center holes, you can stick the PA tubes in there in any orientation.

    First thing to check when you open it up is voltage. Check 6V6 plates, 6V6 screens, then work your way down to preamp tubes. Be careful! It's live, hot and it can bite.

    Look for a broken wire or a bad solder joint.
     
  3. callaway

    callaway Tele-Holic

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    Did it work with the 6JE8? That has a much different pinout from a 12a_7 tube. I think you could have blown your power transformer. I'd pull the tubes and check to see if the power transformer measures open. If not, then leave the tubes out and check that you're getting rail voltage. Then put your original known-good tubes in and check to make sure the plate voltages are correct.

    Be careful!
     
  4. JCMNelson

    JCMNelson TDPRI Member

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    The 6JE8 tube didn't work (as kind of expected) as wasn't in the amp for long at all (less than a minute?). The amp worked after that, but after another change or two stopped working - does that sound llike a blown PT?
     
  5. fezz parka

    fezz parka ---------------------------

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    Is there any hum or hiss coming from the speaker? Check your voltages and do a pop test starting from the power section beck to the input. Where you don't hear a pop, there's your trouble.
     
  6. muchxs

    muchxs Doctor of Teleocity

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    A fully cooked PT won't work at all. If it was loaded enough to blow the fuse should go first. Still, it's easy to check. No voltage on Pin 8 of the rectifier would be a bad sign.

    If the HV secondary is open the amp shouldn't pop when switched off standby.
     
  7. callaway

    callaway Tele-Holic

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    Yeah, it might not be the PT. I was thinking the high voltage winding could be open and the heater/pilot light winding could still be fine.

    Is it possible that the 6JE8 could have caused the 100k plate resistors to blow? Well, should only be about 0.25 W dissipation if they were shorted to ground. You'll just have to dig around and try to figure it out!

    Lesson for anyone in swapping tubes though---don't make the swap unless you're absolutely sure the pinout and ratings are similar. Of course I can't say for sure that the 6JE8 was the cause of the problem, but I'd be highly suspicious of it.
     
  8. Middleman

    Middleman Friend of Leo's

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    Did you check the fuse? Maybe it fried and it's an easy fix.
     
  9. muchxs

    muchxs Doctor of Teleocity

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    Pilot lamp and filaments means fust is o.k..
     
  10. JCMNelson

    JCMNelson TDPRI Member

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    I've just switched it on again and noticed a low hum/grumble. Not too loud but definately there.

    Does that narrow down the issues?
     
  11. fezz parka

    fezz parka ---------------------------

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    Check your wiring in the preamp and if you have the tube amp book by Pittman, on page 141 it'll guide you through doing the circuit disturbance test.
     
  12. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Gold Supporter

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    If it worked fine before tube swapping its likely not a wiring problem.

    Lights on, fuse and PT aren't blown.

    Check your rectifier. Also look for burnt components or arching marks on the tube sockets when you open it up. Look for poor solders, maybe a bad solder finally gave way. Look for wires that may accidentally be contacting other wires or ground (chassis). If everything looks OK, pull out the meter and start measuring voltages - asking us is like shooting in the dark, you'll have to troubleshoot it with a meter and schematic in hand.
     
  13. JCMNelson

    JCMNelson TDPRI Member

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    OK, I've got the 5Y3 on the way (6V6's checked in my RI Champ 600 and they're fine).

    Got the voltages I'll be looking for (my hand is already in my pocket) and I;m opening it up tonight to start checking. I'm pretty p****d off that I've done this, but in a wierd way I'm looking forward to trouble shooting this...

    By the way, thanks everyone for your help, I'm just starting to learn (5E3 was built with my father-in-law) and you guys are being a great help!
     
  14. fezz parka

    fezz parka ---------------------------

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    Poor solder joints would be a wiring problem, Johnny.:)

    Hum coming from the speaker means the power section is alive. Since the problem showed up after tube swapping, check all solder joints on the noval tube sockets. You could have knocked a cold one loose. Check v1 and v2.
     
  15. JCMNelson

    JCMNelson TDPRI Member

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    BINGO!! :D

    A wire on V2 (pin 2) had come loose, and on re-attachment everything is back to normal!! Looks like I haven't fried the PT...

    On a slightly different point, I took the opportunity to check B+ voltage, and it's 415V! I've got a Sovtek in there, is that the only issue? I've got a Jan Philips 5Y3 on the way, so I'll take a reading as soon as it comes.

    Thanks for all the help!
     
  16. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Gold Supporter

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    True :)

    I only meant something was likely not mis-wired.





    Very cool.

    If this happened on one pin, it might be elsewhere too. Check all of your solders again. I had one of my 1st builds work fine until about an hour of playing everytime... turns out my soldering skills sucked bigtime and the heat from the filaments would eventually make the bum solder crack loose.
     
  17. fezz parka

    fezz parka ---------------------------

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    Awesome! To quote Hannibal Smith, I love it when a plan comes together.:D

    [​IMG]
     
  18. koen

    koen Friend of Leo's

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    delete
     
  19. koen

    koen Friend of Leo's

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    delete - wrong topic :)
     
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