B+ Voltage on my 5E3 is 417v - Help!

Discussion in 'Shock Brother's DIY Amps' started by JCMNelson, Jul 7, 2009.

  1. JCMNelson

    JCMNelson TDPRI Member

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    Sorry to hog the forum, I'm a bit of a noob, and this is SO helpful!

    Right, so first thing is to get rid of the Sovtek 5Y3, so I've ordered a NOS Jan Philips. But from what I've read this is only going to reduce the voltage by 20-40v, so I'll still have at least 377v, maybe even 397v?

    My understanding is that the ideal B+ voltage for the 5E3 is in the region of 350v - 360v, is this right? Replacing the PT is not really an option, so how would I go about reducing the voltage to this?

    Thanks for the help!
     
  2. EdMax

    EdMax Tele-Meister

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    #1 Get rid of the Sovtek 5Y3 good for around 40V drop in most cases
    #2 The 6V6's will not all load the circuit the same. If you find that Brand A loads to around 375V, brand B might load down to 350V.
    #3 The bias setting will also influence the anode voltage, recheck your max dissipation. You might need to change out the cathode resistor.

    The 5E3 I just had on the bench 25 minutes ago was running at 363V at the anodes(plates)using JJ 6V6's and an RCA 5Y3.
    20V across the cathode resistor.
    350V on screens
     
  3. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Gold Supporter

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    Using a "proper" 5Y3 will help.

    Is this from a kit, scratch built, or reissue? Is the proper PT being used?

    Biasing the 6V6's right will also help. What cathode resistor value is in there now? Have you measured to calculate for voltage, current, and dissipation?

    Here's the voltages of the 5E3 reissue as listed on its schematic:

    370 (off rectifier)
    320 (after 4.7k resistor)
    250 (after 22k resistor)
    204 (V2, pin 6)
    165 (V2, pin 1)

    My build measures 354 on the plates with a 5Y3. With my SS rectifier switch on, I have 405, which is safe for some modern 6V6's.
     
  4. JCMNelson

    JCMNelson TDPRI Member

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    This is built from scratch using trannies from Ted Weber, and everything (including Cathode resistor is as per original schematic (Fender).

    Haven't even got to biasing the 6V6's (JJ 6V6S), I'm not exactly sure how to do it - I'm still a noob.

    I figure I'll get the NOS 5Y3 and then worry about biasing, I just wanted to get my facts together in the meantime - I'd be grateful for tips on biasing...
     
  5. fezz parka

    fezz parka ---------------------------

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    Do you have the PT with the low voltage taps? I'd switch to those if you do. A 5e3 is cathode biased. Usually it's plug and play. On very rare occasions I've had to adjust the value of the cathode resistor, especially when the B+ is really high.
     
  6. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Gold Supporter

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    Which Weber trannies?

    I'm pretty sure he shows the specs on his site for the PT. If they're meant for 5E3's you're likely OK in that department, it might be a different issue altogether.

    Then again, even with modern "5Y3s" which are not true 5Y3s and yield higher voltages than older NOS 5Y3s you shouldn't be getting 417 voltage... I used Hammond "OEM style replacement" trannies and even with solid state diode rectifiers switched in I'm only getting about 405 on my plates.

    Check to make sure you got the right PT.
     
  7. fezz parka

    fezz parka ---------------------------

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    Also since he's in the UK thangs may be a little different voltage wise...
     
  8. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

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    Yes, definitely check the voltage you're getting out of the wall, it's not always what they say it is... we had this problem at work, where 117v on the wall came out @ 131v... a bit hot, to say the least...

    Franc Robert
     
  9. koen

    koen Friend of Leo's

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    Ok, I feel stupid. Where in the schematics layout is the B+ ? :oops:

    edit: Ah, I found it :p
     
    Last edited: Jul 9, 2009
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