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Duckie is Quiet, 5e3 squealed a bit and then went silent

Discussion in 'Shock Brother's DIY Amps' started by milkshape, Sep 1, 2014.

  1. milkshape

    milkshape Tele-Holic

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    In 2012 I built a DIY 5e3 from sourced parts and the help and encouragement of people here at this wonderful forum, you can see it here: http://www.tdpri.com/forum/shock-brothers-diy-amps/313314-duckie-another-5e3-tweed-deluxe-born.html#post3929359 Last night right before a practice it squealed for a second and went silent. What's funny is I had not a half an hour before we got together warmed up a bit and it was fine. I did notice a slight acrid smell and the second 6v6 was blue plating a little but soon stopped. No smoke visible, transformers cool, caps don't seem to be popped or puffy. Checked what if it is not the amp things like the cable between guitar and amp, took the effects out of the equation, tried cable and guitar in another amp. I have been very lucky with my builds any issues were small, obvious, and easily fixed. Entering exciting territory for me, fixing is an opportunity to learn a lot more. I guess next step is getting the B+ voltages? Is there troubleshooting guide or outline people like to follow? Look at stuff coming off the rectifier first, then look at ... Help appreciated in any form, thanks, milkshape


    Update: closer examination showed showed the 4.7k resistor between the first and second filter caps is toast. That and probing showed no voltage on B+1.
    Fixing now, hopefully this is it.
     
    Last edited: Sep 1, 2014
  2. Telephonic

    Telephonic Tele-Meister

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    Keep us posted, threads like this are a great resource for people like me and a good challenge for the seasoned pros on here. :)
     
  3. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I'm by no means an expert amp troubleshooter but I'd pull all the tubes and follow Paul Ruby's startup guide.
     
  4. milkshape

    milkshape Tele-Holic

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    I think the toasted resistor was a symptom as opposed to the problem. I replaced it and switched power on and put it on standby, no smoke, switched it off of standby and the rectifier sizzled a bit and then the fuse blew. I suspect the rectifier tube is done, I checked for shorts and did not find any. I have a spare rectifier in the 5f1 I built but am shy to try it until I get some feedback on whether my suspicions are sound. More research on the net at large is most likely how I will be spending my evening ;) Thanks everyone.
     
    Last edited: Sep 1, 2014
  5. ripgtr

    ripgtr Tele-Holic

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    New rectifier tube or NOS rectifier tube? I have read a fair bit on modern rectifiers failing. Not from personal experience. All mine are old, they came with the amps and rectifier tubes seem to last a long time.
     
  6. milkshape

    milkshape Tele-Holic

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    Hey ripgtr thanks for the comment, it's a sovtek, new guy. So we have a fireworks show in the rectifier bottle. Pretty sure that's not the operating norm, going to try my other rectifier tube and if that proves to be the issue replace rectifiers in both the 5f1and 5e3 with NOS tubes.
     
    Last edited: Sep 1, 2014
  7. milkshape

    milkshape Tele-Holic

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    Images of the toasted resistor
     

    Attached Files:

  8. milkshape

    milkshape Tele-Holic

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    Swapped out rectifier tubes, the one from the deluxe worked in the champ, and the one from the champ shoots sparks when power is applied in the deluxe. Guessing either a short or a bad power transformer. I will go over the connections with the multimeter, but the amp does not move often and I just can't see a short suddenly appearing. I mean vibration can move things around but enough to produce a short? Ideas welcome!
     
  9. Commodore 64

    Commodore 64 Friend of Leo's

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    How about a pic of the guts? Maybe we might notice something.

    I would have guessed a bad rectifier tube, but you already ruled that out.
     
  10. milkshape

    milkshape Tele-Holic

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    Thanks c64 I will get a shot up, the amp has been perfect for 2 years and gets used almost everyday. So I don't believe it is a wiring issue. This is the first time I have opened the back on it in I can't remember how long. So I don't think it is a wiring issue. But more eyes the better. I have a feeling I will be replacing the power xfrmr.
     
  11. hackworth1

    hackworth1 Friend of Leo's Vendor Member

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    Shorted power tube screen grid in either tube (pin 4) will cook that resistor. Might also short second filter cap.

    Install new Power Tubes and new 4.7k to 5K 2 watt resistor and try it.
     
  12. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Save yourself some tubes and follow Paul Ruby's startup guide. His guide gives you specific things to look for and will allow you to troubleshoot issues with the least damage to the rest of the amp. It starts with no tubes in the chassis and measuring voltages and progresses with tubes being added in a controlled manner.

    Yes, your burnt resistor is the symptom of something that is allowing way too much current to flow--most likely a short.
     
  13. milkshape

    milkshape Tele-Holic

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    Compared the voltages coming off the power transformer of the deluxe with those of the champ. I first removed the rectifier. The champ is steady 480V at pin 5 and 6, while the deluxe is all over the place but never more than 65+/- V. It's crazy, numbers never stay quiet, just keep flipping around

    Hackworth - thanks for the reply, so you think perhaps the tube is shorted or the short exists outside the tube? I did notice that the second 6v6 did do a little blue plating when the problem first showed up.
     
  14. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Is the power transformer center tap securely grounded? A loose ct ground will cause funky problems.
     
  15. milkshape

    milkshape Tele-Holic

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    Thanks robrob, I will double check that. Was not able to get to it over the weekend. I remember an issue with the heater tap not being grounded and learning about the 100 Ohm y wired to ground trick to eliminate it. The stuff you find here can save time time time. So many newb builders such as my self have gone from 0 to tone by being helped from past and current threads and knowledgeable members. Chances are someone has done it or broke it just like you. Long Live TDPRI.
     
  16. milkshape

    milkshape Tele-Holic

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    I replaced the resistor and got some new tung-sol tubes but unfortunately this did not cure duckie. I am going to take the chassis out and give it a good visual and electrical inspection to make sure everything is on the up and up. I will post voltages and findings.

    I have a sneaking suspicion it is the power transformer. Right now when you turn it on, the rectifier tube sparks, red plates something fierce, and blows the fuse. Even after that the rectifier works fine in the champ I have.

    All shots in the dark welcome.

    I got the tubes from tubedepot, first order there and was impressed. I fat fingered my address and sent them a note. They responded quickly, like minutes, let me know it was fixed and the tubes arrived earlier than expected.
     
  17. Commodore 64

    Commodore 64 Friend of Leo's

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    I have a bad PT that had that exact same behavior with the rectifier tube. I have 47 ohm resistors on the leads to my rectifier and one of them got so hot it melted the solder on the rectifier pins in about 4 seconds.

    When I need a PT ASAP I go with a Hammond from Angela: http://angela.com/hammondclassicenclosedplateandfilamentpowertransformers.aspx (Hammond drop ships)

    When I can wait 4-6 weeks I go with https://www.edcorusa.com/

    Another good option is Classictone: http://www.triodestore.com/classictone.html
     
  18. milkshape

    milkshape Tele-Holic

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    Thanks Commodore 64! that is the kind of similar experience I was looking for. I see a new power transformer in my future.
     
  19. milkshape

    milkshape Tele-Holic

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    Links were helpful, thanks!

    Does Edcor really want $21 to ship it UPS ground!? Man, that's practically 1/2 the cost of the tranny! NE is not the dark side side of the moon. Nice lookin' stuff tho'.
     
  20. Viejo

    Viejo Tele-Afflicted Silver Supporter

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    I was gonna suggest you listen to Hackworth but then I saw you allready have.
     
    Last edited: Oct 26, 2014
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