1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Transformer and choke positioning

Discussion in 'Shock Brother's DIY Amps' started by Tom Kamphuys, Jun 4, 2020.

  1. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    For my JCM800 6V6 build I was planning to use an upright PT. I need the space inside the chassis. I thought it was fine if I just rotated the PT 90 degrees wrt the OT. However, I found a YouTube video ' Transformer Orientation' by DeepBueHarp clearly showing the benefit of a lay down PT. So I would like to use a lay down PT and raise it above the chassis. I can imagine some aluminium strips, or a small hammond chassis as a ' foundation'.

    Has anyone done this before? Other ideas?

    And secondly, where should I place the choke? Electrically it should be between the PT and OT. That way it would also screen the OT from the PT. But what about the effect of the field of the choke on the OT? A lot of amps have the choke on the other side of the OT. What would be the benefit of that?

    I know thousands of amp have been build with upright PT's and chokes al over the place. But this is a research/learning project for me, so simply copying stuff is not my goal. I'm also planning to test this (in reality), but I first need to know whether I need to buy a lay down or an upright PT.
     
  2. Badside

    Badside Tele-Meister

    Posts:
    461
    Joined:
    Jul 5, 2011
    Location:
    Montreal, Qc, Canada
    I've built 2204's (aka single channel JCM800) with laydown and upright transformers, both with EL34 and 6V6 power tubes, and hum was never a problem.

    The video you're referencing is coming at it more from a hifi point of view. Marshall made a legacy out of amps with upright transformers.

    Don't overthink it too much. If upright is more practical for your layout do it.

    Look into the "headphone trick" to figure out positioning of the OT. Hint: as long as it's 90 degrees off and not right against the PT it's usually not an issue.
     
    awasson, King Fan, Paul G. and 2 others like this.
  3. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    5,992
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    ^^^ super logical. As a smaller deal, re the choke, I'd definitely try it between the PT and OT. As you say, the wires want to be there, and in my recent 5G9 build I learned Fender did it this way in a ton of amps, with both large and small chokes -- and some pretty close spacing.
     
  4. The Ballzz

    The Ballzz Tele-Afflicted

    Age:
    65
    Posts:
    1,717
    Joined:
    Apr 11, 2016
    Location:
    Las Vegas, NV
    @Badside

    Please be so kind as to either share the "headphone trick" or at least a link to it? I know I read it (here, I think) a few weeks back, but can't find it now!

    Thank You,
    Gene
     
    Last edited: Jun 4, 2020
  5. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    It's in Blencowes book section 3.11. It is basically what is done in the video I mentioned. Hook up the PT to 120/240V (only) and connect a headphone to the secondary of the OT. You can find a position where the hum is low (enough).
     
  6. schmee

    schmee Doctor of Teleocity

    Posts:
    13,424
    Joined:
    Jun 2, 2003
    Location:
    northwest
    I have put OT and PT oriented the same, close together etc. Just not had an issue. There may be amps where it is, I dont know but I dont worry about it much.,
     
  7. Badside

    Badside Tele-Meister

    Posts:
    461
    Joined:
    Jul 5, 2011
    Location:
    Montreal, Qc, Canada
    Good point! Sorry I was on mobile and didn't want to badly explain it

    Here's more info: http://ax84.rru.com/FAQs/general.html#hp-trick

     
  8. The Ballzz

    The Ballzz Tele-Afflicted

    Age:
    65
    Posts:
    1,717
    Joined:
    Apr 11, 2016
    Location:
    Las Vegas, NV
  9. dan40

    dan40 Friend of Leo's

    Posts:
    2,041
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    The headphone trick works great if your transformers must be mounted very close to each other. Once you get 3-4" separation between them on the chassis the noise reduces to almost nothing.
     
    awasson and King Fan like this.
  10. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    I get that the general consensus is that it should not be necessary. However, this is a learning, researching and overthinking build.

    So, what if I still want to do it, how could/should I do it?
     
  11. Mongo Park

    Mongo Park Tele-Afflicted

    Posts:
    1,004
    Joined:
    Nov 28, 2010
    Location:
    Winnipeg
    Hook up your power transformer as in the headphone trick and the connect your op transformer to your volt meter one lead to black and the other to 16 ohms or 8 ohms of you don’t have 16 ohms. Set your meter to millivolts. Powers up the power transformer and see what you pick up. it is easy and super accurate.
     

    Attached Files:

  12. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    Ok, you guys convinced me. I'm going with an upright PT.

    I think...
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,648
    Joined:
    Dec 30, 2019
    Location:
    california
    Either stand up or lay down are fine. The stand up is great when the chassis does not already have a cut-out.;)
     
  14. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    This is what I am intending to use:

    Screenshot_20200610-183417.png

    Looks like the IEC cut-out will be easy, so I won't have the trouble of making it (as discussed in a recent thread).
     
  15. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    I've made a wooden dummy chassis and mounted some hardware. Good I did that as I had some mistakes in the drawings.

    I performed the headphone trick. First I tried to use a scope, but it didn't work out. Using an actual headphone worked like a charm.

    IMG_20200630_223112473.jpg

    The minima in the hum occur for seemingly random orientations; parallel to the PT is not significantly worse than perpendicular.

    I have to move the OT quite far away (see image) to have no audible hum. Would the above location have an influence on the signals in the preamp circuit? Would you route the OT wires outside or inside the chassis? Shortest route or clearing the tubes?
     
    Last edited: Jul 1, 2020
  16. dan40

    dan40 Friend of Leo's

    Posts:
    2,041
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    Several amp manufacturers have chosen to mount the OT at the opposite end of the chassis with good results. The only issue I can see would be the long runs of wiring needed to make it work. Running the wiring on the topside would work but be sure to encase each wire run in something to keep them safe.
     
  17. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    After testing some more, I have found that there is a minimum in the hum very close to the PT and choke. I only have to raise the OT ~10mm and place it at some weird angle. Has anyone of you guys ever done that? How would you accomplish that? Would be nice if it was adjustable (locking nut?). The minimum is very 'small'.
     
  18. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    630
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    I repeated the experiment with the actual chassis. Outcomes differ. I actually managed to make a movie. I connected the OT leads to the microphone in of my phone. It's even more sensitive than a headphone.

     
    LetItGrowTone likes this.
  19. dan40

    dan40 Friend of Leo's

    Posts:
    2,041
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    I actually had to tilt my OT a few degrees one time to get rid of the last bit of audible hum. The amp is still working fine today and very quiet. You will always want to test the positioning on the actual chassis you are using because the chassis itself forms a bit of a shield and will cause changes in the radiated noise from the PT.
     
    tweedy_woodpecker likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.