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5e3 Rectifier (5y3) voltage

Discussion in 'Shock Brother's DIY Amps' started by mcentee2, Feb 11, 2019.

  1. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    ....another hour, another question...

    My 5e3 pre-built chassis has a 230v Primary PT, as such everything is running *slighty* hot on 240v mains. The tube plates are ok as per other thread, and I am happy with them and the tube dissipation numbers I have.

    .... but the 6v6/12a.7 filaments are running at 6.9v and the 5y3 rectifier at 5.4v - just about in spec, but I would be more comfortable with them a bit lower.

    I would like to bring them down to 6.3v / 5v and am planning on putting the right resistors in series as per advice around and instructions on @robrob pages.

    I've worked out the values for the drop and the right wattage but all the example I can find are done on the 6.3 power/pre tube heater circuits.

    Can I do this for the 5v 5y3 filament circuit as well ? ie find the right resistance for the drop required then get two resistors of half that value and put them in series on both sides of the ac feed to the 5y3 ? Does it being carried on the high end of the HT affect this in any way ?
     
  2. rogb

    rogb Tele-Holic

    909
    Jan 3, 2012
    London, England
    Assuming you have a centre tap (red/yellow?) on your PT, you could use a Robrob Zener stack, to lower your B+?
    [​IMG]
     
  3. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    B+ is fine, as stated in original post, my question was about taking the rectifier Heater/Filament AC down from 5.4v to 5v.
     
  4. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    Bump for the afternoon/evening crowd!

    Anyone know if I can bring rectifier tube filament voltage down the same way as other 6.3v based filament tubes via two dropping resistors?
     
  5. Urshurak776

    Urshurak776 Tele-Meister

    493
    Jul 2, 2004
    Charlotte
    I'm no expert, but I don't think it is necessary. I assume the components are rated for at least that voltage?
     
  6. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    I wouldn't worry about 5.4vac. Any reference to ground would carry the rectified vdc with it.
     
    Wally likes this.
  7. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    5y3 rectifier is rated for 5v, my build measured 5.4v, which although doesn't sound a lot is enough over spec!
     
  8. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    43
    Mar 1, 2010
    Kent, OH
    Spec is +-10% right? 5.5V?

    You are on spec.

    I wouldn't worry for a second about 5.4V on the fils, personally.
     
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  9. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    Many thanks, I haven't seen many comments that say it's fine at that level :)

    However, do you know where these specs are? The 5y3 sheets I can find just state the nominal value and not any accepted variance?
     
  10. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    43
    Mar 1, 2010
    Kent, OH
  11. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York

    Thanks for the link, however my reading of it is possibly different to yours.

    Most of it is around too *low* voltage and its effects.

    It also mentions the variance built in re 10%, however that is to cater for a spikey supply where the nominal voltage can vary up or down.

    My voltage is already 10% higher than nominal, so it has nowhere to "safely" flex upwards.

    I do think I need to bring it down and I know how to do it on the 6.3v tubesb.

    My question is if that same method can be applied to the 5y3 heater voltage that rides on top of B+.
     
  12. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    If you must. You could add dropping resistors in series with the 5vac supply. to drop .4vac on a 2 amp load you would use .2 ohm resistance. use 2w resistors. One .4r2w on each leg? I have never done this so its totally theoretical.

    V(drop)=I(current in amps) R
     
    Last edited: Feb 13, 2019 at 9:37 AM
  13. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    Many thanks, indeed it is that method I am proposing to use - the one shown on @robrob 's 5e3 mod page.

    I just would like someone to practically confirm if the 5y3 can be treated the same as the 6v/12ax7 in that regard - I am the same as you, only theoretical so far.

    I worked it out as a 0.1r on each leg though!

    Total r= 0.4v / 2 A = 0.2r = 2 x 0.1r(2w)
     
  14. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    parallel resistors 2x.1=.05r

    2x.4=.2r

    This is why I said theoretical. The heater supply is one coil of wire right? I would think this makes the added resistors in parallel to each other. That is why I doubled the value.
     
    Last edited: Feb 13, 2019 at 10:06 AM
  15. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    Hmm.

    This is a series resistance, but split across both sides of an AC supply, hence total divided by two.

    They aren't parallel.

    https://robrobinette.com/Generic_Tube_Amp_Mods.htm#6.3V

    "
    Desired voltage drop / amps = resistor ohms



    .5 volt drop / 2.7 amps = 0.19 ohm dropping resistor



    We want to keep the voltage balanced on each heater pin to reduce 60Hz hum so we need to use two resistors, one on each pin

    We divide the 0.19 ohm by 2 to get 0.095 ohm (I rounded up to 0.1 ohm)"
     
  16. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Cool. Sounds like you have a plan. Let us know how it works.
     
  17. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    Lol:):)
     
  18. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    43
    Mar 1, 2010
    Kent, OH
    Adding components that will get hot and potentially fail to a system that is within a perfectly safe operational envelope would seem to defeat the purpose of your efforts.

    Really, I don't know why in the world you are choosing to obsess over this. A used 5Y3 rectifier is dirt cheap. I have a drawer full of 'em. Put a couple protection diodes on the rectifier and find something else to modify in the amp that might relate to something audible like tone.
     
    Nickfl likes this.
  19. mcentee2

    mcentee2 Tele-Meister

    281
    Feb 18, 2011
    York
    So far you are one of the few to respond, so thank you for that.

    As to "obsession", I asked a question for something I don't know myself.

    I still don't know the answer, maybe not many do, fair enough, but in the thread I did help someone else understand something they had got wrong.


    Sorry about that.

    Yes the rectifier has protection diodes already so that is good.
     
    Last edited: Feb 13, 2019 at 12:23 PM
  20. rogb

    rogb Tele-Holic

    909
    Jan 3, 2012
    London, England
    ??? You wrote "everything is running slightly hot" so lower the B+ a few volts. It won't affect anything with lower plate volts by a small % + or - but at least your AC will be closer. I doubt 6.9v is really much to worry about though.
     
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