Home Forums Design and Building 2 Stroke Amplifier Design and Building Hammond PT for a Two-Stroke (Rev 2) Amp?

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  • #8006
    Todd
    Participant

    I am I first time tube amp builder and I would like to use a Hammond PT to build 2nd revision of the Two-Stroke Amp.

    I want to use a Hammond PT because I live in Canada, have a local supplier (NextGen https://nextgenguitars.ca) 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.

    Starting with the Fender replacements 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 power lamp + 12ax7 + one of 6V6/6L6/EL34)

    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. Is this a problem?

    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 I see:

    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 …

    #8007
    Andy
    Keymaster

    From what I recall the 290AX is the one you want. The 22772 has 2A for the filament so that should be fine there. You’ll need about 70mA on the secondary so that is good too.

    #8008
    Todd
    Participant

    Thanks @ajswanson

    I was wondering if the higher filament amperage spec is left over from the original two output tube design…

    #8009
    Todd
    Participant

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

    The consensus is that the Hammond 290 AX (https://www.hammfg.com/part/290AX) 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 (https://www.hammfg.com/part/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.”

    #8012
    Reggi
    Participant

    Hi…the Hammond 200 is fine. 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.

    #8340
    Mark
    Participant

    Just chiming in on this old thread to confirm the 290AX works fine. I just swapped the AES 022772 PT that I used initially for the Hammond 290AX to try to compensate for the high line voltage at my house (125VAC), which was presumably resulting in a pretty high B+ of 425VDC with the AES PT. To get the B+ down, I used the 275VAC secondary (red/white pair) instead of the 325VAC secondary (red pair). It brought the B+ down to 375, which is still a little high, but seems tolerable. I’m not finding the 290AX to run hot at all, yet. I’ve only had it cranked (volume on 8-12) continuously for about 30 min at most. It only got slightly warm. The amp is getting a great grinding tone around 5-10, then starts to melt down past that. When it’s wide open it starts compressing like crazy, kinda like a fuzz pedal, and cutting out slightly. Think Neil Young, but maybe even worse. 🙂

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