Not another JTM45 build!

Discussion in 'Building the Classics' started by jessemhopkins, Jul 26, 2020.

  1. jessemhopkins

    jessemhopkins Member

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    The bright channel breaks up around 2, the normal channel around 4. I suppose I can roll some tubes in the preamp, but I’ll save that for once it’s stable. So far, it has only blown fuses with power tubes installed.
     
  2. william vogel

    william vogel Well-Known Member

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    Light bulb limiter and check for excess current draw.
     
  3. Chris-in-LA

    Chris-in-LA Well-Known Member

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    I haven’t checked my JTM45 with Metrospec iron but your initial b+ is about 100 volts higher than the manual shows, which is about 400v, not 500v. Didn’t you get that Merren PT from a forum member? Maybe it’s not the right PT.
     
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  4. jessemhopkins

    jessemhopkins Member

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    PT is correct and voltages have all settled down now. I didn’t record the exact B+ but it was somewhere right around 450. Higher than the metro but the same as what Neil and others reported on either Merren or original Drake. I’ve still got another pair of KT66 now to try, I’ll pop them in and take some measurements shortly.
     
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  5. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Good luck. Mine is very close to the Metro specs, almost exactly the same on the power tubes and rectifier, but 20 volts over on V1 and V2. The PI is mixed, p3 and p6 are 20 over, p3 and p8 are 10 under. Below is the Metro specs for reference if anyone is asking.

    upload_2021-1-31_12-31-51.jpg
     
  6. jessemhopkins

    jessemhopkins Member

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    I’m pleased to report that I got this amp up and running stably this weekend. With the aid of a friend, we noticed the rectifier had failed in addition to a bad solder joint on one of the output tubes. Retouched the joints, swapped the recto, we’re in business. Only thing left is for me to pin the badge @neikeel sent across the pond on it. I’ll grab some pics and shoot them over later.
     
  7. jessemhopkins

    jessemhopkins Member

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    Here's the finished amp atop my 4x12. An absurd amount of lessons were learned along the way, as they always are, but I'm so glad to have this one done and it sounds fantastic. I'm still dialing in the tone for my setup, but truly superb. Not much noise unless it's cranked, and I likely won't have much occasion for that.

    A massive thank you to everyone who helped me out and lent their expertise to this relative noob, especially to @neikeel and @william vogel for your long-suffering during the troubleshooting phase. It feels a bit silly now to put the coffin badge on it, knowing how far off in many ways the look is, but I'll put it on until I build a proper replica someday.

    Onto the next one!
     
  8. adew1

    adew1 Active Member

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    Looks great!
     
  9. neikeel

    neikeel Well-Known Member

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    Need final final pic!
     
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  10. jessemhopkins

    jessemhopkins Member

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    Haha ok, I’ll have to swing by the hardware store first. I’m taking it out for a real world test at church this weekend.
     

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