Yet another 5E3 build...PT questions...

Discussion in 'Amp Tech Center' started by ianb3432, Jul 2, 2017.

  1. ianb3432

    ianb3432 TDPRI Member

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    Hello, been a while since I've been on here. Well currently I'm looking to do another 5E3 Tweed Deluxe build, but I had a couple questions regarding the power transformer and hoping someone could help me out...

    This time my idea is to build the 5E3 in a 2x12 tweed twin cab, but also I want to use a 5E7 chassis, because I figure it will make it easier for modifications, given the extra space in the chassis, and extra potentiometer holes. Plus I think the ground switch would be great for the NFB switch mod while also having the standby and power switches.

    My only concern though is the cutout in the 5E7 for the PT will have difficulty with mounting the 5E3 PT, so I'm wondering if I could avoid that hassle and use a 5E7 PT for the build. I'm looking at both weber 5E7 and 5E3 PT's and trying to determine if it will work, with decent results. Here are the specs for the two:

    https://www.tedweber.com/media/import/w022798sch.JPG (This is for the 5E7)

    https://www.tedweber.com/media/import/w025130sch.JPG (This is for the 5E3)

    So it looks like both tube filament secondaries should work fine, but my question is for the 5E7 PT, would the red/white secondaries at 660V on the 5E7 PT work for the 5E3, which looks like it requires 680V? Or would that run the two 6V6s too cold and not sound great? Or is there a relatively easy way to lower the 720 voltage on the 5E7 PT to get more into ideal 5E3 voltage territory? And also does the extra 50mA of current play a big factor on the bigger PT for a 5E3?

    If its too complicated and easier just to find a way to make do mounting the 5E3 PT in the larger chassis hole, I'll just go that route...maybe I'm just over thinking the whole thing...either way, thanks for your input!
     
  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The 5E7 should be fine. With today's wall voltage a 330-0-330v power transformer will run higher voltage than the late 1950's. The 5E7 should be just about perfect. You also have a fixed bias tap available for a fixed/cathode bias switch.
     
  3. ianb3432

    ianb3432 TDPRI Member

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    Thanks for the input! I think I will go that route for the PT...next thing I was wondering...which OT would be the best match with the Weber 022798 PT? The stock OT they have for the 5E3 kit is 6.6k for the primary and the 5E7 OT is 4k...will either work just fine or is the difference in the primaries going to have a significant difference in tone/output? Also I should probably mention I plan on running the build on the standard 5Y3/6V6 tweed deluxe setup.
     
  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Then use the 5E3 6.6k or better yet use a multi-tap OT so you can run 6L6s too.
     
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