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first build 5e3 - question on tubes and parts

Discussion in 'Shock Brother's DIY Amps' started by agent_zed, Aug 22, 2019.

  1. tubegeek

    tubegeek Friend of Leo's

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    LED = Light Emitting Diode
     
  2. andrewRneumann

    andrewRneumann Tele-Holic

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    I didn’t see it anywhere in the schematic or layout either.
     
  3. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The original deluxe had a two prong power cord. The old schematics show a .05uF cap as a *death cap* for that two prong power cord. I am pretty sure that is why it was included with the kit. I know of no one who would install a death cap. It could be used for different applications though.

    It is nice to have that cap supplied should you want to mod the normal or bright channel. It would cut some bass if it replaced one of the .1 coupling caps.

    For your build it is redundant.
     
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  4. agent_zed

    agent_zed TDPRI Member

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    well i know that much :) it was more the fact that it worked both current directions which it shouldn't do so must have additional diodes.

    thanks all for the sanity check on the additional cap. Glad it might be useful in the future at least, rather than sitting in a box for the rest of eternity.

    Snuffer stick made and i've double checked all my connections and tightened all nuts/bolts. Hopefully get time to go through power testing today.

    thanks
     
  5. agent_zed

    agent_zed TDPRI Member

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    So with a healthy dose of fear i plugged it in and started doing the testing as per the instructions from stewmac.

    Pilot light came on no worries (so the LED seems to be doing it's job). Slight hum from the transformer. So far so good
    Tested filament voltage on the v1 pins (9 - 4/5) and got 6vac which is between the 5-7 specified. happy days so far.
    Plugged in the 5y3 as per instructions, got a red glow off the valve/tube, and tested the b+ voltage on the board (pin 27) and it returned ~460v which is way over the specified ~386v.

    So i turned it off and discharged the caps and have come in to do some research.

    This post https://www.tdpri.com/threads/my-5e3-voltages-are-too-high-everywhere-what-to-do.116164/ says that the high voltage can be due to fully charged caps. The advice appears to be to put in the power valves and it should drop to normal.

    A) Does this seem like a good plan? Should i measure any other voltages first
    B) is it only the 5y3 and 6v6s at this testing stage or all valves installed?

    many thanks

    so close now.... :)
     
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  6. D'tar

    D'tar Friend of Leo's

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    voltages without a load will be high. A bulb limiter is a good thing.... Reduces fear by a whopping 90%:D

    https://robrobinette.com/5e3_Modifications.htm#Light_Bulb_Current_Limiter

    Proceed at your own risk. You should check voltages throughout the circuit where you expect to find B+ and check to make sure its not where it shouldn't be as well. Then add your preamp tubes, recheck. power tubes recheck... Follow the startup guide.

    https://robrobinette.com/Tube_Amp_Startup.htm

    Without a bulb limiter a 500mA fuse is recommended until you are sure you have no issues.
     
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  7. David Barnett

    David Barnett Doctor of Teleocity

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    D'tar is right.

    If nothing's drawing current, the voltages will be high. What you're seeing is normal.
     
  8. agent_zed

    agent_zed TDPRI Member

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    Thanks both sorry for late reply.

    She makes sound !!!! :)

    ...well kind of.

    So i followed the advice and built a bulb limiter and turned it all on with that. All seemed ok so plugged in a guitar and as if by magic it was amplifying YAY

    So i removed the current limiter and upped the fuse to the 2 amp slow blow.

    Still have sound so moved the volume 1 knob a bit and it got louder. Tone changed with the tone knob but if i engaged the vol 2 it started to break up the sound not in a nice distortion type way but a hiss kind of sound.

    I didn't get chance to test for long before it suddenly started to make a weird noise through the speaker so i stomped on my emergency power cut out switch and stopped it. Can't really explain the noise easily it wasn't feedback more of a weird sci fi noise that would probably have gone into a squeal if left on if that makes any sense.

    It's late now so i can't turn it on to test again so will try again tomorrow and check all the voltages etc.

    I guess it'll be hard to advise anything without further intel but anything obvious to check?

    On the bright side the few clean strums i heard sounded nice so pretty excited to test it properly.
     
  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Congrats on getting it fired up!

    The volume/tone pots on a 5e3 can get some odd noise when they are set fairly high. With standard parts there can be blocking distortion at louder volume.
    When the unused channel is at a higher volume setting it can suck some tone. Essentially the signal can find a path to ground through the B+ of the unused channel.
    This doesn't sound like what you are describing though.

    Do you have a negative feedback resistor mod on this amp? If so you may need to swap the OT primary wires to address a positive feedback issue.
     
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  10. D'tar

    D'tar Friend of Leo's

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    Show us your voltages!!! All tubes each pin. Photos are welcome and can save pages of troubleshooting text!
     
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  11. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    ^^^ exactly. While we wait for voltages (nice job @agent_zed) note that StewMac uses Mojo kits and Mojo includes a death cap *but doesn't connect it.* I guess just for visual authenticity? Of course an orange death cap is nightmarishly inauthentic...
     
  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Blue vs Orange... meh
     
  13. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Heh, it's less painful to die of electrocution than of ugly amp visuals....
     
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  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I suppose you are right, but the smell of burnt hair makes my eyes kinda squinty, just like when I see ugly amp innards.

    :lol:
     
  15. agent_zed

    agent_zed TDPRI Member

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    Just had look again this evening and fired it up and listened for a while and it began to do the weird thing again. Then i remembered that 1 of the 2 12AX7's that i had kicking around had done something weird when i tested it in another amp ages ago. I thought i had the good one in but turns out as soon as i swapped it out it's all good :)

    I then also realised that i'd put it in the wrong position so swapped the 12ax7 with the 12ay7 and it all sounds pretty good to my ears :) haven't cranked it yet as it's always late when i get out to the garage but played around for a few minutes and tried the controls which all responded well.

    I haven't got all the voltages just yet but i checked a few. Sorry it's not complete yet. Do these help at all so far?

    rectifier pin 8 = 341v
    6v6s pin 2-7 = 6v, pin 8 = 19.9v
    V1 pin 1 = 127v, pin 8 = 1.7v

    What are the most important ones to check?

    I'll get some photos up soon. It's still out of it's case so i'm really excited to get it all looking like it should and hopefully it will distract from the completely inauthentic colours in my amp! I don't even have the fake standby switch!

    Big Thank you to everyone who has helped me, it's really appreciated.
     
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  16. jtcnj

    jtcnj Tele-Holic

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    Congrats on getting this far, and staying alive in the process.
     
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  17. agent_zed

    agent_zed TDPRI Member

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    Omg does it sound good! even my GF could tell it sounded a lot better than previous times she's heard me play (the tone not the technique, the technique is still rubbish).

    I seem to have loads of clean headroom. I really had to crank it right up to get the overdrive and although it was only for a few mins (as it was loud!) it was some nice sounding overdrive. Certainly nothing i've achieved in the past with pedals etc.

    I have a concern though and i'm hoping it is just the way it's meant to be (I suspect not). When i switch it on from cold it does the quiet bit before it's warmed up but then it makes quite a loud humming noise like if i was holding the ends of the lead. After a few minutes it drops away and is almost silent and back to giving a lovely sound.

    If the amp has been on recently then this doesn't happen leading me to believe it is to do with heat.

    Is this just the valves warming up? a loose connection? or have i likely got a bigger problem somewhere?

    Thanks
     
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  18. agent_zed

    agent_zed TDPRI Member

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  19. andrewRneumann

    andrewRneumann Tele-Holic

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    Did you mean this literally? Like 3 minutes for the hum to go away?
     
  20. agent_zed

    agent_zed TDPRI Member

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    yeah literally 3-5mins. I read a couple of other forums and people have suggested it's the power tubes causing the problem. I don't know how likely that is. I don't have any spares. The only thing i can try first is swapping out the V1 preamp tube as i have access to a spare 12ax7. It won't help if its power tubes but at least it will be one thing ruled out.

    Forgot to add this noise is independant of volume settings or even if the guitar is plugged in!
     
    Last edited: Sep 13, 2020
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