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Power transformers questions

Discussion in 'Shock Brother's DIY Amps' started by screefer, Nov 28, 2020.

  1. screefer

    screefer Tele-Holic Silver Supporter

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    I'm teeing up a few projects and wish to enjoy some local sales.
    The larger the order the better shipping rates.

    The first two projects are definitely a Harvard and a Champ and then maybe a Deluxe micro. I am very inexperienced at this (but totally hooked) having only built one 5f2a, so please bear with me.

    I will probably go with Hammond(s) as they can be sourced here, but I've included specs for a 40-18027, TP-25, and a Mojo760EX for comparison.

    Hammond 290AX; Hammond 290CAX; CT 40-18027: Allen TP-25 Mojo 760EX

    ma = 100 ... 115 ... 100 ... 150 ... 75

    Volts = 650/550 ... 630/550 ... 630/550 ... 620 ... 330

    Heater
    CT = yes ... no ... yes ... yes ... no

    Bias tap = no ... no ... no ... yes ... no

    Weight = 2lbs. 15oz. ... 4lbs. 1oz. ... 4.5lbs. ... 5.1oz ... 3.4 lbs.

    My first question is why the weight differential between them especially the AX and CAX?
    And indeed, what are we getting for the extra weight?

    Next, the 5f10 calls for 305v. but when I use the lower voltage I get 328v. with this formula
    (275 X 1.414 - 60v. ) and I get 343v. using this calculator...https://thesubjectmatter.com/calcptcurrent.html

    My wall shows 121 volts and I realize that can be an issue.
    How important is that 305v. target? If so, would a zener string be the route to go?
    The 5f1 doesn't pose an issue regarding B+ v. with the AX or CAX?

    Which Hammond tranny (they are the same price) would you all recommend for the 5f10 and which for the 5f1?
    It seems that the AX would suffice for both (and it has a heater CT) but I've read lots on here recommending the CAX specifically for the 5f10.

    The Micro calls for the 40-18027 and apparently it can also be used for the full blown 5E3.
    Would the AX work for the Micro seeing as how the milliamps are the same as the 40-18027?

    Thanks for any help and please straighten me out if I'm not thinking this correctly.
     
    Last edited: Nov 28, 2020
  2. James Knox

    James Knox Tele-Holic Silver Supporter

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    The Hammond 290AX has what you need for both 5F1 and 5F10 AND they are on Sale 10% off a AES through Dec 1. The 290AX is my favorite for 5F1s and I’m just finishing a 5F10 Harvard with one now.

    Also, the Classic Tone will be hard to find with them have gone out of business.
     
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  3. screefer

    screefer Tele-Holic Silver Supporter

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    Thanks. We've got the same deal up here Northside.

    Interesting to see what your B+ ends up at?
    Great build you got going on!

    Wonder why the bulkier CAX (more wires and weight) gets so much love?
     
  4. James Knox

    James Knox Tele-Holic Silver Supporter

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    I used that one once, I think it was on RobRobs Micro Deluxe. It has the International Wiring options, more taps, etc if I recall correctly.
     
  5. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    If you haven't purchased any power transformers yet, I say to expand your search and try to find something that will do the job as closely as possible, without needing to plan for a bunch of Zener diodes to make it work.

    Note that the Deluxe Micro doesn't draw very much current, being just two "preamp" tubes and optionally a rectifier tube. So if you get a power transformer that's rated for 150mA or whatever, it's not going to sag very much and your B+ may end up much higher than some online calculator will tell you. The Hammond 269GX or 269JX might work really well here, since they're older designs expecting only 115V from the wall.
     
    Last edited: Nov 28, 2020
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  6. DrewB

    DrewB Tele-Afflicted

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    Definitely do your best to avoid using "thumbtacks" to get the job done.
     
  7. screefer

    screefer Tele-Holic Silver Supporter

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    Thanks
     
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