Advice: Hammond PT for a Two-Stroke (Rev 2) Amp

Discussion in 'Shock Brother's DIY Amps' started by maccullt, Feb 28, 2019.

  1. maccullt

    maccullt TDPRI Member

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    I am I first time tube amp builder and I would like to use a Hammond PT to build the 2nd revision of the Two-Stroke Amp from Dave Hunter’s book

    I want to use Hammond PT because I live in Canada, have a local supplier (Next-Gen), and Hammond have a good reputation.

    I am undecided which transformer to pick and I am looking for help from experienced builder especially ones that have built this amp.

    The Tube Amp Network hosts a copy of the layout and the schematic

    The book suggests one of:

    Mojo760
    Secondary: 330-0-330 VDC @ 75mA
    Filament: 6.3V @ 4A
    Rectifier: 5V @ 4A

    P-TF22772
    Secondary: 325-0-325 @70mA
    Filament: 6.3V @ 2A
    Rectifier: 5V @ 3A

    Weber 125P1B
    Secondary: 330-0-330 100mA
    Filament: 6.3 V @ 4A
    Rectifier: 5.0 V @ 3A​

    Or any transformer for a tube amp with:

    Secondary: 310-0-310 to 330-0-330 VDC at least 70 - 80mA
    Filament: 6.3 V @ 4A (note: the schematic from the Tube Amp Network says 2.7A)
    Rectifier: 5.0 V @ 3A​


    Hammond Transformers

    Starting with the Fender replacements at the Hammond classic 290 series I see :

    Hammond 290 AX
    Secondary: 325-0-325 VDC @100 mA
    Filament: 6.3V @ 2.25 A
    Rectifier: 5 V @ 3A

    The filament voltage is low but according to the Hammond site this is the replacement for for Fender parts 125P1B and 022772.

    Would 2.25A be too low for this amp (this would be powering the lamp + 12ax7 heater + heater for one of 6V6/6L6/EL34).

    I wonder if the higher filament amperage is a left-over spec from the first revision of the amp which could have two power tubes ...


    Hammond 290 CX
    Secondary: 325-0-325 VDC @207 mA
    Filament: 6.3V @ 4A
    Rectifier: 5 V @ 3A

    The filament amperage is correct but the secondary is amperage is high - 207ma vs the 100ma or less for the other PT

    Hammond 290 CBZ
    Secondary: 325-0-325 VDC @120 mA
    Filament: 6.3V @ 4A
    Rectifier: 5 V @ 3A​

    This seems to be closer to what I need according to the original spec.​


    Looking at the Hammond classic 200 series


    Hammond 272 DX
    Secondary: 300-0-300 @144 mA
    Filament: 6.3V @ 4A
    Rectifier: 5 V @ 3A

    The 300-0-300 is lower than the spec’d 310-0-310 minimum ​


    Looking at the Hammond classic 300 series I didn’t see anything closer …

    Thanks for reading this far!
     
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  2. Mikey_Boss

    Mikey_Boss TDPRI Member

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    Hi, my 2 cts

    Not that experienced, but 12ax7 = 300 mA, 6v6 about 500 mA, 6L6 would be 900 mA, el34 would be 1,5A. So running a 12ax7 and an el34 would need 1.8A

    BR

    Mikey
     
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  3. magic smoke

    magic smoke Tele-Meister

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    The schematic looks like a modded out champ. Mikey Boss has the right math, 290 AX should work fine. You may want to change R4 from 68k to 34k for less attenuation on the input.
     
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  4. gigante

    gigante TDPRI Member

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    One of their recommended PTs (P-TF22772) only has 2A of filament current. I don't know why in the "Or any transformer for a tube amp with" section they recommend 4A

    but this seems like a reasonable guess.
     
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  5. magic smoke

    magic smoke Tele-Meister

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    BTW, Dave Hunter’s guitar amplifier book was my first introduction to this fascinating world. Please post a build thread and read as much as possible.

    You should probably try to build directly from the schematic, the layout you linked has some puzzling symbol choices and at first glance might not be the same revision.
     
    Last edited: Feb 28, 2019
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  6. maccullt

    maccullt TDPRI Member

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    Thanks to everyone one who chimed in on Guitars Canada, Tube Amp Network, diyAudio, and TDPRI (http://www.tdpri.com)

    The consensus is that the Hammond 290 AX should be fine for the Two-Stroke.

    Some other interesting observations:

    “There have been reports that the 200 series can run hot, and can even buzz IIRC, so if you are the type who wants extra quality and is willing to spend more to get it, then the 300 series is better.”​

    The 291AEX is an “upgrade” version of the 290AX and in addition to supporting export voltages​

    “291AEX uses high grade 29M6 magnetic steel laminations for reduced losses, more surge output power, cooler operation & longer life.”​
     
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  7. Mongo Park

    Mongo Park Tele-Holic

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    So are you thinking point to point for this build
    It is easier to follow the schematic and gives you a better understanding of what is happening.
    Cheers. Yes Ron
     
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  8. Mongo Park

    Mongo Park Tele-Holic

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    Looks like you can pick up from Nextgen, sweet.
     
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  9. sixstringer

    sixstringer TDPRI Member

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    Regarding 68k vs 34k resistor for R4, you can just leave that resistor out all together and the amp works fine. You won't gain or lose any input signal gain with any of those.
     
  10. KellyWalrus

    KellyWalrus TDPRI Member

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    I'm just populating my board now. Did you end up finishing this project?
     
  11. maccullt

    maccullt TDPRI Member

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