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Sizing wire for heater circuit... (5E3)

Discussion in 'Shock Brother's DIY Amps' started by DrPepper, Apr 5, 2021.

  1. DrPepper

    DrPepper Friend of Leo's

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    I'm building a 5E3 clone'ish amp. Getting ready to wire the heater circuit. I have 18 & 21 ga solid core copper on the way but, the way I am routing I might come up short with the 18 ga. but, I ordered plenty of 21 ga. By the numbers, the 21 ga. should be rated at over 3.5 Amps from what I can find ... So, 21 ga. should be sufficient, right?(2 12**7's and 2 6v6's)
     
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    You'll be fine.
     
  3. Muzzy

    Muzzy TDPRI Member

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    Use the 18 to wire the power tubes and convert to 21 for the preamp tubes. That's usually what I do anyway.
     
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  4. DrPepper

    DrPepper Friend of Leo's

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    Thanks
     
  5. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    On my last build, a hybrid, I only had one tube. At first, it was very noisy. Then I re-wired the heater circuit using a shielded two-conductor instrumentation cable for the heaters. This wire consists of 2 insulated 18 gauge wires (twisted) and a tinned, 18 gauge drain wire. The wires are jacketed together with foil shielding. I attached one end of the drain wire to my ground bus and it significantly reduced the hum. I think the only way to use this wire effectively with multiple tubes would be with dedicated runs, no daisy-chaining, so it might clutter up your build if the design has a lot of tubes. I'd guess it's about 1/4 inch in diameter.

    20210405_093637.jpg
     
  6. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    Heater voltage is only 6V. Electric fields will be small. The current is high and thus the magnetic field also. Shielded wire does not protect against 50/60Hz magnetic fields.

    Keeping the two conductors close does help, twisting them even more. That might have caused the improvement you mention.
     
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  7. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    That's good to know. I used it because I had it on hand and I thought it might help.
     
  8. schmee

    schmee Doctor of Teleocity

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    I avoid 18 ga on them all now. Been using the standard Fender gage used on all but the heaters for a long time. No issues even in 6 pre tube amps. The stiff 18 ga puts a lot of strain on things, especially today's thin cheap tube socket tabs.
    The "aha!" moment occurred after taking apart old Hammond organ chassis that had like 16 tubes in them... all driven by tiny heater wire.
     
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  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    5E3 only has 4 tubes on that filament string. 22AWG is fine.
    It is easier to manipulate the smaller wire.
    It also fits into the terminals easier.
    KISS... don't bother with the 18AWG... Marshall didn't. hah.
     
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  10. dan40

    dan40 Friend of Leo's

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    22awg for me also.
     
  11. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Another 22ga convert. I believe a guy named Jim Marshall was an early adopter...
     
  12. Urshurak776

    Urshurak776 Tele-Afflicted

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    A buddy of mine wired his 5E3 scratch build with 22GA radio shack hook-up wire. Everything. Works fine. That was a little over a year ago. No issues so far.

    Edit: It was a 5F1.....still okay I would think.
     
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