5E3 voltages / high plate dissipation

Discussion in 'Shock Brother's DIY Amps' started by Joe Les, Sep 28, 2020.

  1. Joe Les

    Joe Les TDPRI Member

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    I just finished building a 5e3 from scratch with a couple of the rob Robinette mods (switchable coupling caps, switchable NFB) and it sounds great but I'm getting a couple high voltages on V1 as well as high plate dissipation on the 6V6s and was wondering if I should be concerned and if there's much I can do about it.


    B+1: 373

    B+2: 335

    B+3: 260


    V1 - EH 12AX7

    1: 178

    3: 1.4

    6: 172

    8: 1.4


    V2 - EH 12AX7

    1: 171

    3: 1.3

    6: 209

    7: 19

    8: 50


    V3 - RCA 6V6

    3: 360

    4: 336

    8: 20


    V4 - RCA 6V6

    3: 364

    4: 337

    8: 20


    Plate current: 40mA

    Plate to cathode: 339V

    =13.6W

    I think everything looks fine except for the 13.6W plate dissipation on the 6V6s, the voltages on pin 1 and 6 of V1, and also the B+3 seems a little high. Everything else seems to be pretty close, if not slightly high. Also, I am using a classictone 40-18016 PT and a JJ 5Y3S rectifier.
    Thoughts?
     
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  2. D'tar

    D'tar Friend of Leo's

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    Hey Joe!

    Those numbers look really good IMO!

    How does it sound? You can play with dropping resistors... Other tubes etc. But I would just play!

    We all love pictures! Hint!
     
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  3. King Fan

    King Fan Poster Extraordinaire

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    What he said. :)

    If you view 6V6GTs as 14W tubes (many informed folks have started doing this) you're actually under 100% dissipation, and even if you take 'em as 12W tubes (which is nice and conservative) you're 'only' at 113% -- which is actually safe and even desirable in cathode bias, is in the range these amps typically run, and should be well tolerated by decent 6V6s (especially good ol' RCAs). And of course D'tar is right about the other voltages too.
     
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  4. jimgchord

    jimgchord Tele-Afflicted

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  5. jimgchord

    jimgchord Tele-Afflicted

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    Not really a big deal. 6v6 is closer to 14w diss anyway. You could run a string of 10v, 5 watt zener diodes between the pt center tap and ground to bring it down if you want
     
  6. King Fan

    King Fan Poster Extraordinaire

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    FWIW, my 5E3 with a 40-18016 runs about 115% dissipation on modern wall voltage (~120-122), sounds insanely great, and has never eaten a 6V6 -- even tho I run late-40s Ken-Rads, which some might see as less robust than RCAs...

    Now, that said, I did build a vintage voltage adapter / bucking transformer, and with wall voltage knocked down about 10V the amp also sounds killer -- less modern, a bit mellower or bluesier. But my adapter box has a 'standard' outlet in it too, and the amp sounds awesome either way.
     
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  7. Joe Les

    Joe Les TDPRI Member

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    sounds good thanks for the replies! Now that you guys mention it I remember reading about the 12W vs. 14W debate for 6V6s. I still need to build a cab but here are some pics of the chassis: IMG_1865.JPG IMG_1860.JPG IMG_1863.JPG IMG_1862.JPG IMG_1861.JPG IMG_1864.JPG
     
  8. Joe Les

    Joe Les TDPRI Member

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    Also this is only my second build so lead dress suggestions etc. are welcome
     
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  9. King Fan

    King Fan Poster Extraordinaire

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    That's a nice tidy build; I'm not the smart guy to trace the whole circuit or verify each component, but overall I'm gonna say you did a fine job.

    What's going on here? Is that a splice without heat shrink? Or???

    And I can't see where your household ground/green anchors, but I assume it does. :D

    upload_2020-9-28_9-4-7.jpeg

    Not to critique but hoping maybe to make your life easier, tweed builds are hard enough if you use well-behaved wire. Is that fatter wire (eg, the white) just really thick insulation, or is it also heavier than 22ga?
     
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  10. Joe Les

    Joe Les TDPRI Member

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    Good point about the lack of heat shrink on that splice, looks like I missed that haha. I'll definitely fix that. My household ground is hidden under the power chord in that pic so you can't see it, but it's attached to a power transformer bolt. And yeah the thick white wire is some that I got from tube depot. It's 22ga but for some reason the insulation is really thick which makes it kind of a pain but it's what I had so I used it and it ended up working out alright. Definitely will avoid it in the future though.
     
  11. jimgchord

    jimgchord Tele-Afflicted

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    Better practice is to have the safety ground on its own dedicated fastener.
     
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  12. Jlwctn

    Jlwctn Tele-Meister

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  13. Joe Les

    Joe Les TDPRI Member

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    It sounds great!! I'm really happy with how it came out. The NFB mod is also really cool.
     
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  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Nice looking build!

    Your 250R bias resistor gets very hot. There should be some space in between the bias resistor and bias cap.
     
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  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I used the classictone 40-18016 with old GE 5y3. I also used the classictone 40-18022 OT on 3 recent 5E3 builds. (the 3rd 5E3 has a 12ax7 in V1)
    With 120v from the wall
    B+ 374, 369, 364
    B+2 331, 330, 316
    B+3 245, 243, 247

    V1 JJ 12ay7------- EH 12ax7
    1: 133, 131 ----------166
    6: 130, 126 ----------163
    8: 1.95, 1.88 ---------1.32

    V2
    1: 166, 168, 167
    3: 1.13, 1.15, 1.21
    6: 199, 199, 202
    8: 45, 46, 45

    I have 13W Russian 6V6 substitutes for power tubes. So we maybe comparing apples to oranges with power tubes... but pin 8: 22, 23.7, 21.1

    As you can see the 12ay7 have lower plate voltages than the 12ax7.
    For sound I prefer the 12ay7 in these three builds.

    I think your build is in the ballpark. For giggles you could use higher resistance for the dropping resistors. I doubt you would notice a difference even if you brought the voltage down a tad.

    I do recommend a 12ay7. OMMV.
    Enjoy:cool:
     
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  16. King Fan

    King Fan Poster Extraordinaire

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    +1 on trying a 12AY7.
     
  17. Joe Les

    Joe Les TDPRI Member

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    Thanks for all the info; that's good to know. I was kinda wondering if using a 12ay7 would make a difference in plate voltage. I haven't tried a 12ay7 yet just because I don't have one and my local guitar shop is currently out of stock, but once I get one I will definitely give it a go to see how it compares sound wise and voltage wise.
     
  18. Nickfl

    Nickfl Friend of Leo's

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    The voltage across your cathode resistor includes screen current as well as plate, you should subtract 5% or so screen current from that 40ma. So with 38ma actual plate current your dissipation is really about 12.9w or 92% if you call those 14w tubes. Well within spec for a 5e3.
     
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  19. JamesAM

    JamesAM Tele-Meister

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    I’ll echo everyone above and agree that your numbers look fine and your build looks great!

    I wish I had a classictone PT available for my build earlier this summer, but they were backordered for months due to Covid. I used a Hammond 290bx and my numbers are a bit hot- looks like yours are a-ok, especially for those RCAs. I had to up my cathode R to a 330r to get in the right ballpark, which was actually pretty close to your numbers if I can recall correctly.

    the only thing I would say is to stay away from tung sol 6v6, as the consensus seems to be that they are true 12w tubes and can’t handle the hotter bias from modern higher wall voltages. Mine redplated even at about 100% dissipation, which should be fine for a cathode biased amp. Most NOS are much hardier and will handle higher voltages better, and your RCAs are considered by many to be the best of the best. I’ve got JJ 6v6Ss in mine, and they sound fine and are right at about 94% dissipation.

    the tung sols sound awesome, though. I bet your RCAs sound fantastic.
     
    Last edited: Sep 29, 2020
  20. GoKart Mozart

    GoKart Mozart Tele-Meister

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    Looks fantastic!!
     
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