Kt66 Jtm45 Build

Discussion in 'Building the Classics' started by Outlaws, Mar 3, 2018.

  1. Outlaws

    Outlaws Member

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    I have built a few 5E3 heads with a mix of kits and sourcing, and want to do a JTM 45. I guess some are higher wattage than others? I want to keep it more around the 30-36 watt original. I am not a stickler for 100% dead on original copies of everything, but that is sort of where I want.

    What are the popular options. It seems most chassis mounting is all over the place... 2 cans inside, 1 inside 1 ontop... nothing even close to standard transformer cutouts and mountings....

    That transformer issue seems to be the crux of the whole choice. I had good luck with Classictone and would just assume use those again, but then it comes down to which chassis I can use and what layout/BOM I should choose.
    I am teetering on Triode or Ceriatones layout (sans the power switching and loop), Mojotone I don't know if they are going for max wattage or what, I have alreadys read theirs are tighter sounding (maybe the Heyboer trannys?).

    Thoughts?
     
  2. neikeel

    neikeel Well-Known Member

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  3. stickyfinger

    stickyfinger Active Member

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    Valvestorm is the closest to a original you can buy but doubtful its 100% accurate.
     
  4. Outlaws

    Outlaws Member

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    I don’t care about 100% accurate, I just want to make sure it’s more on the original at the lower wattage as I some advertise as being 45 watts and others say some are stiffer.

    But they do t mention the tranny cutout specs from what I see.
     
  5. Outlaws

    Outlaws Member

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    This chassis on Valvestorm seems to offer the use of any transformer but I don’t see how that’s possible. Is there are adaptor plate they give you once you specify which tranny you bought?
    Also, it’s aluminum.... isn’t that bad? Looking at these images they are running grounds to the chassis without any other wiring connecting those ground lugs together. I am under the impression aluminum isn’t safe to wire like steel.
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    It's the power supply B+ that makes it lower / higher wattage.

    Using Classic tone, the voltage taps might be change-able.
    Using a transformer for a rectifier tube, you have a range of voltages to choose from.
    (that's why I used classic tone, it has minus 20% taps)

    There are 3 rectifier tubes, and a SS rectifier which can allow 4 different B+ voltages.
    Then if the transformer has taps, you increase that choice to 8 different voltages.

    Sooner or later with some trails: I settled on 400V B+. But I had all kinds of choices to go up or down in wattage.
    (I made it 15 watts, triode) I could have gone up to 50 watts...and down to about 10.
     
    Outlaws likes this.
  7. S.Marshall

    S.Marshall New Member

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    Most JTM 45 transformers will have the same bolt pattern or very close.

    As far as aluminum goes that is what the originals are made of. I've been making these chassis for almost 10 years with no issues. Build it right and keep it maintained and you'll have no issues.
     
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  8. ampmadscientist

    ampmadscientist Well-Known Member

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    Just because something was made for many years, does not mean that the safety rules weren't changed.

    Since this amp was designed, the codes for electrical safety have been updated.
    That is why newer aluminum amps are built differently from the older aluminum amps....to meet codes for safety.

    The newer amp does not use the aluminum as a circuit current path. The current path has been isolated from the chassis.
    The chassis is still grounded, just not used as the current path. That's the difference.

    The old design uses the chassis as the current path (unless you update it).

    You will see that the aluminum chassis is bonded to the mains earth, and that connection is high-current tested to meet a safety requirement.
    Basically, every amp must meet:
    No high voltage leakage to the chassis. (hipot test) No high voltage leakage between conductors (insulation breakdown test)
    Ground withstands high current (ground bond test)
     
    Last edited: Mar 9, 2018
  9. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    There is no amp manufacturer that does a "hi-Pot " test on amps. Quit with your dribble, it's beyond getting old.
     
  10. S.Marshall

    S.Marshall New Member

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    You're talking about current codes and I'm talking about copying an original JTM 45 in a Valvestorm chassis.
     
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  11. danfrank

    danfrank Well-Known Member

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    Just use these where you attach ground to chassis. These dig into the aluminum and provide a secure electrical contact to the chassis:

    Int-ExtStarLWshrs.gif

    ExtLockStarWshr.gif
     
    Outlaws likes this.
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    EVERY amp / component manufacturer is required to do hipot tests, ground bond tests.
    It's the law.
    UL requires these tests.

    These laws were created to ensure electrical safety...
    something you obviously know nothing about.

    (I do these tests professionally)

    If the hipot test or ground bond testing fails, it is not legal to sell the appliance.
     
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  13. ampmadscientist

    ampmadscientist Well-Known Member

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    No.
    Dissimilar metals used to bond aluminum are prohibited.

    a. Chassis is no longer used as a current path.
    b. Oxide between 2 dissimilar metals will form a perfect insulator.
     
    Last edited: Apr 28, 2018
  14. stickyfinger

    stickyfinger Active Member

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    A aluminum ground lug and a aluminum chassis is A-OK to ground pins 1+8 on the power valves at the socket?

    Now I need to go see what the ground lugs are made of.. lots of amps of mine that I no longer own potentially have dissimilar metals even in steel chassis amps.
     
  15. danfrank

    danfrank Well-Known Member

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    Grounding pins 1 & 8 to the chassis is not good as it makes the chassis a ground return path, which will make an amp noisy. Yes, I know Marshall did it but Marshall did a lot of "less than ideal" things in the manufacture of their amps, especially early on.


    This is not directed at you, it's a general observation of mine, but I don't know why so many people that clone these amps want to do everything exactly like the originals. Electronically speaking, the originals had a lot of bad implementation in them. A clone will never be an original, period. So what's with the obsession to make a clone exactly like an original, when it can be made better. As in less noise, less hum, etc.
    I was asked to look into repairing an AC30 "handwired" reissue... I opened it up and was amazed at the craftsmanship in this amp. Very good! BUT they used carbon comp resistors, which are noisy as hell, and of course this amp has an intermittent noise problem. LOL! It seems that amp makers are more interested in building something new just like the originals instead of building it more reliable than the original. Even though this handwired reissue AC30 uses metalized polyester caps and LEAD FREE SOLDER!!! Ha Ha! Dumbasses!
    For those of you that aren't electronically inclined, lead free solder is useless and equipment made with it breaks down all the time. Bad solder!

    End of rant...
     
    Last edited: Apr 29, 2018
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  16. stickyfinger

    stickyfinger Active Member

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    What?!? Hum is tone!
    Seriously these low gain NMV amps are very quite imo and “better” has methods are not need. My builds and metal panels are very very quiet amps if following original layouts.
     
  17. toadfish

    toadfish Member

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    So what's better than carbon comp resistors (like NOS Piher's) newbie here so please educate me!!
     
  18. stickyfinger

    stickyfinger Active Member

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    Nothing wrong with carbon comp! They do have a noise but remember that what gets amplified is also part of the tone! So those Vox amps use them because it’s part of the sound of the amp.

    Piher would be historically correct for most 45s
     
  19. toadfish

    toadfish Member

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    Thank for that stinky finger I mean Stickyfinger:facepalm::hbang:
     
  20. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    Nice thread! Looking forward to your build thread
     

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