5f1 build with Hammond 125ase OT

Discussion in 'Shock Brother's DIY Amps' started by Tele Slacker, Mar 26, 2020.

  1. Tele Slacker

    Tele Slacker TDPRI Member Silver Supporter

    Posts:
    94
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    Building a 5f1 champ, using the referenced output tranny. For this circuit, which secondary should I use? Looks like it’s dependent upon primary impedance. Suspecting there’s more than one good answer, any caveats?

    Equally important... why? Teachable moment!

    upload_2020-3-26_21-50-57.jpeg

    Thanks all!
     
  2. drew1d

    drew1d TDPRI Member

    Posts:
    59
    Joined:
    Jun 30, 2014
    Location:
    Westchester NY
    I use the 5000 ohm primary (6v6). with the appropriate impedence of the speaker. If your using a 4 ohm, green I suppose. Hope that helps.
     
  3. Mongo Park

    Mongo Park Tele-Holic

    Posts:
    723
    Joined:
    Nov 28, 2010
    Location:
    Winnipeg
    The op transformer has to match the correct impedance of the power tube you are using as well as the speaker you are using.
     
  4. drew1d

    drew1d TDPRI Member

    Posts:
    59
    Joined:
    Jun 30, 2014
    Location:
    Westchester NY
    I was looking at the specs on the 125ase. I don’t think you can use that in a champ. It’s only 3 watts, and can only handle 25ma. If you go with it, You may have to change the bias resistor so it sends less juice to the transformer. Or, not care and just run it. Hammond stuff is well made and holds up past it’s specs for sure. I’ve only built 2 amps both single ended. I’ve used a 125dse. For a Princeton style amp, and used a el-34 for a power tube. (So I used the 2500 primary instead). I couldn’t get the B+ voltage from the filter caps down enough to where I wanted it. So I went with a power tube that could handle it. (The power supply ma and filament could handle it). Good luck.
     
    Tele Slacker likes this.
  5. Tele Slacker

    Tele Slacker TDPRI Member Silver Supporter

    Posts:
    94
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    I’m using this with a Hammond pt, using the 275-0-275 HT tap (lower B+). Running 6v6 obviously, into a 4ohm speaker.
     
  6. tubegeek

    tubegeek Tele-Meister

    Age:
    59
    Posts:
    137
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    Basically as you move up from ASE to BSE to CSE etc., you will get a larger standing current capability as the cores are larger and larger. Since the last thing you want in a Champ is beefy low end (which is what you lose first as you approach core saturation) I would suggest that you get whichever Hammond approximates the size of the Champ's transformer - IIRC the ASE is just the one size smaller, it's probably for All American Five table radio replacements.

    If you oversize the transformer, say a DSE, it'll be able to drive a "real" cabinet with more low end. But you run the risk that it actually won't sound as good through a Champ-style speaker - too much low end coming through that the speaker won't be able to handle well.
     
  7. King Fan

    King Fan Friend of Leo's

    Posts:
    4,753
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    That's a slightly confusing little OT. Somebody's gonna ask: Why that one? :)

    But assuming you have it already, IIRC, the original 5F1 was 17K:4ohms.
     
  8. Tele Slacker

    Tele Slacker TDPRI Member Silver Supporter

    Posts:
    94
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    “Somebody's gonna ask: Why that one?”

    Fair question... easy answer: poor proofing of order - didnt catch the 3-watt reference. But I have another heyboer properly spec’d around here. ;)
    So alls well that ends well.

    Appreciate all the help... everyone.

    and in the words of Buddy Miller: “Keep your distance”

    Strange days.
     
    tubegeek and King Fan like this.
  9. Tele Slacker

    Tele Slacker TDPRI Member Silver Supporter

    Posts:
    94
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    Not a continuation of the output transformer question, per se... but I’m seeing some strange behavior from the volume pot (see attached YouTube link):



    Metered the pot resistance from ~3 to wide open 12 (pot clicks on at about 3). As you can see below, there is a disproportional change from ~8 - ~11. Very little change above 10 (up to 12).
    upload_2020-3-29_18-4-19.png

    I don’t expect a perfect transition... just haven’t seen this with other 5f1 builds. Significant difference from 5f2a build in side by side noise, and volume pot response. Pot seems a little out of tolerance ... 1M pot reading 1.2M... ~18% difference...

    thoughts?
     
  10. King Fan

    King Fan Friend of Leo's

    Posts:
    4,753
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Not sure about the taper. Somebody smarter than me is needed. :)

    Re the noise, do you mean the pot turns noisily, or the amp is noisy? If the amp, and if your 5F2a has a separate power switch, that could do it -- the 120V household power on the back of a 5F1 on-off volume pot is basically sitting right on top of our little tiny input signal.
     
  11. Tele Slacker

    Tele Slacker TDPRI Member Silver Supporter

    Posts:
    94
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    Overall, slightly more noise than other builds (including another 5f1). I may try the RobRob HT center tap to 8uF cap ground in your thread.

    wondering if I need to order another pot... or may do a workaround to see if it’s the pot/switch combo.
     
  12. King Fan

    King Fan Friend of Leo's

    Posts:
    4,753
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    If the amp's all built it may be hard to drill in a separate power switch and use a normal pot — but it’d be quieter and the pot might just work better.

    I like your workaround idea. For noise testing just unplug, lift the 120 off the pot, splice it safely outside the amp, and plug in to turn on...


    Sent from my iPad using Tapatalk
     
  13. Tele Slacker

    Tele Slacker TDPRI Member Silver Supporter

    Posts:
    94
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    Thanks for the responses on all of this. In the spirit of providing the teachable moment referenced in the original post (matching output xformer primary impedance to speaker load), Uncle Doug has a very informative video that addresses this. I might have to watch it once or thrice to digest content (slow learner).

    Hope that might help anyone else who’s searching.
     
    King Fan likes this.
  14. zook

    zook Friend of Leo's

    Posts:
    2,506
    Joined:
    Aug 6, 2003
    Location:
    Cochise, AZ
    Where did you get this information? That is a very high primary impedance for a 6V6.
     
    Tele Slacker likes this.
  15. King Fan

    King Fan Friend of Leo's

    Posts:
    4,753
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    You're right, it's nice to give a source. I recall learning about 17K many years ago when I found out the 5F2a OT was not the same as the 5F1 OT. Since then, I've seen that discussed in a lot of threads, and yeah, I was always struck by the 'unusual' 17K. Maybe somebody smarter than me can point out how 17K:4ohms was a useful (5W, SE) setup?

    As for a published source, Classictone reverse engineered their 40-18110 ("This output transformer was directly designed from the one in an actual vintage 1958 Fender* 5F1 Champ** amplifier.")

    upload_2020-4-3_9-1-46.png
     
    Last edited: Apr 3, 2020 at 11:29 AM
    Tele Slacker and tubegeek like this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.