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Yikes! 5E3 DMM readings -- I now know why everything seems high

Discussion in 'Shock Brother's DIY Amps' started by RustySterling, Oct 12, 2018 at 1:29 AM.

  1. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    I'm attaching a JPEG spreadsheet of my DMM readings on my Tube Depot 5E3. I've had a problem with high voltages not just on this amp but also my recently built 5F2A. Turns out, my household voltage is 123.5VAC. Yikes! I measured at a few outlets and get the same thing. I know current back in the '50 was around 110-112VAC, so my modern voltage is really high.

    There is other strangeness about this amp -- which is working BTW. On the rectifier Pins 1 and Pin 7 should read 0 but the DMM jumps around with rising and falling VDC on both those pins. I know that isn't right.

    Not sure about other values but here is the JPEG of the spreadsheet. I hope someone will look at them and let me know if they are way out of line.

    Oh, and B+ VDC: 1 = 386; 2 = 343.1; 3 = 264.6
    5E3VoltagesCropped-1.jpg
     
    Last edited: Oct 12, 2018 at 6:17 PM

  2. Wyatt

    Wyatt Tele-Afflicted

    Nov 3, 2004
    Your household voltage is average for modern day.

    I would have expected the Tube Depot PT to be compensated for the higher wall voltage. Almost every repro transformer maker offers at least a compensated option.

    It’s really the only the V1 voltages that seem +50% high.
     
    Last edited: Oct 12, 2018 at 9:02 AM

  3. Urshurak776

    Urshurak776 Tele-Meister

    353
    Jul 2, 2004
    Charlotte
    My understanding is you want the power tube pin 3 voltages to be around 360V (ideally.) However, your 380V with JJ 6V6 tubes shouldn't be a problem at all. As @Wyatt mentioned, your V1 voltages are high. I guess that is power transformer dependent. I'm not sure what power transformer tube depot provides in those kits.

    I am also building a 5E3 (thread is on here also) and my household voltage is around 122.6 average. I picked a power transformer that is supposed to be designed around this modern voltage. Classic Tone 40-18016

    http://www.classictone.net/40-18016.html
     
    Last edited: Oct 12, 2018 at 10:40 AM

  4. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
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  5. Urshurak776

    Urshurak776 Tele-Meister

    353
    Jul 2, 2004
    Charlotte
    @D'tar, I saw another thread that said to do the dropping resistor before using the Zener diodes for noise reasons. Have you ever heard that?
     

  6. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    @Urshurak776 Using the same Classictone 40-18016 PT. So what might be causing high voltage on V1? And up +50% seems pretty significant.

    @D'tar I know about the Zener diodes from The Professors thread on his 5F2A. He had good luck with it. And I'm noting what Urshurak said about dropping resistor. I'll have to explore more.

    The thing that is perplexing and concerning to me is the high V1 voltage. I'm going to post my B+ voltages later. Any ideas what might cause such high reading on V1? Additionally, it seems to me that voltages on the rectifier are high. Or am I reading those incorrectly?

    Also, does anybody have any idea why Pins 1 & 7 on the rectifier would have anything on them? Those are free pins and AFAIK should read 0-VDC or VAC.

    I wish @robrob would take a look.
     

  7. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    Can you define "jumpy" ? If you're just seeing it go crazy with numbers less than a volt or so, I wouldn't be worried at all. It's just trying to pick up whatever it can, and since that tube pin is just floating out in space you're picking up random data.
     
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  8. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    @corliss1 Yeah, I thought that it might be random data. On my 5F2A I get proper readings of 0 on those pins but on the 5E3 it is just crazy. Maybe I'm overthinking that as an issue.
     

  9. Urshurak776

    Urshurak776 Tele-Meister

    353
    Jul 2, 2004
    Charlotte
    Do you have another rectifier tube and another 12ax7 or 12ay7 you could try?
     
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  10. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    Yes, I have those. I'll give that a try.
     

  11. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    OK, here are the B+ VDC: 1 = 386; 2 = 343.1; 3 = 264.6

    Also readings on C3 = 1.463VDC; C6 = 1.365VDC; C10 = 21.89VDC

    I also checked my grid resistors values and they are all fine and within spec.

    And I'm attaching the layout and schematic of this Tube Depot kit.

    5E3Schematic.jpg
     

    Attached Files:

    Last edited: Oct 12, 2018 at 6:01 PM

  12. magic smoke

    magic smoke Tele-Meister Silver Supporter

    241
    May 28, 2017
    Quantum Entanglement
    Are you using a 12ax7 or 12ay7 in v1? I’ve experienced increased plate voltages when substituting preamp tube types
     
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  13. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    JJ 12AX7 in V1 and V2. I'll try a 12AY7 in V1 and we'll see.
     

  14. Nickfl

    Nickfl Tele-Afflicted

    May 24, 2016
    Florida
    Those voltages aren't tremendously out of line IMO for a kit build. The commonly used transformers in many kits often yield B+ close to 400v for a 5e3. 170 on plates of V1 is a little high, but not nuts, note that the preamp plates on the 5F11 are around 160v. You said you checked the grid resistor values? Did you check the plate and cathode resistor values on V1 as well? Those are the ones that would be likely to throw off your voltage or bias.

    I'm more concerned about your power tube bias. If you used the 250 ohm cathode resistor as per the schematic, then you are over 100% dissipation (even for a JJ), something closer to 90% would be more conventional. You might consider upping it to a 280 or 300 ohm cathode resistor, though that will end up pushing your voltages up a bit further. Don't get too hung up on B+, these amps can sound good anywhere between 340 and 400v and if you want to pull it down closer to likely vintage specs, just use zeners.
     

  15. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    @Nickfl Thanks. I appreciate your input. I put in a EH 12AY7 in V1 and that tamed some things. Pin 1 at 122.7 and Pin 6 at 122.0; but P3 now reads 2.091 vs. 1.482 previously, and P8 now reads 2.081 vs. 1.48.

    BTW, cathode and plate resistors test in spec. And I just may change that cathode resistor from the 5W 250ohm to a 10W 300ohm. I'd really like to put more singing tubes, like the EH 6V6, in this amp and don't trust they would last in the present circumstance.

    Oh, and the noise I hear once it warms up and I dig in I'm beginning to be convinced that it is speaker breakup. I've been playing with the back open, facing me, with lights out and don't see anything strange with the tubes when it starts. I'm hoping that will smooth out once these speakers are broken in. And that little sizzle seems more like a character of this particular amp right now.
     
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  16. Urshurak776

    Urshurak776 Tele-Meister

    353
    Jul 2, 2004
    Charlotte
    Using Robs bias calculator you are at 109% dissipation. Like Nick said above, a 300 ohm cathode resistor will put you in the low 90's. A 270 ohm is about 101%. The 300 should be perfect. Hopefully your B+ will be below 400V, so you would have to check that.
     

  17. SacDAve

    SacDAve Poster Extraordinaire Silver Supporter

    Age:
    66
    Dec 23, 2009
    Rocklin Ca.
    I did some readings on one of my 5E3's house current 118 then the same Amp I used a Variac and lowered the current to 110. Overall the sound of the Amp was about the same at 110. The Variac did add some hiss. I can't remember what classic tone PT I used in this amp. I'm thinking of trying a 300ohm cathode resistor or a zener diode string. I also use a 12AY7 in V1 don't care for the 12AX& in V1.
     

    Attached Files:

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  18. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    @SacDAve I like you chart better than mine.

    I really prefer 5751s or 12AY7s, which I had in the amp previously. Went to the 12AX7s during trouble shooting phase because I wanted to follow Rob Hull's design specs. But I still prefer the lower wattage preamp tubes and will stick with one of them in V1 (EH 12AY7 right now). I have ordered a 10W 300ohm resister to swap out with the cathode bias resistor now in her.
     

  19. SacDAve

    SacDAve Poster Extraordinaire Silver Supporter

    Age:
    66
    Dec 23, 2009
    Rocklin Ca.
    Can't wait to see the results of the 300 ohm. I did a mod on one of my 5E3's someone posted. I did use a 300 ohm.tThe amp was stock before I did the Mod.(250 ohm) hears the voltages before and after o_O. This Amp never really sounded very good I used all metal film resisters after the Mod it sound even worse. I probably be redoing the Amp soon.
     

    Attached Files:

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  20. RustySterling

    RustySterling Tele-Meister

    230
    Jun 4, 2018
    Carmichael, CA
    @SacDAve I have the screen and grid resistors installed on the sockets with the same values you noted. That was part of the original build. The filter caps in mine are 22uf, so I'm happy with that. What does the 1000pf (.001uf) on the tone pot do better than the .0047uf? Oh, and I used all carbon comp resistors except for dropping resistors on filter caps.

    I'm pretty happy with the tone of my 5E3, which, with the 2x10s, isn't really a 5E3. I do have a Proluxe in a standard Deluxe cab with 12". I'm thinking of swapping the two amps, which would make the 2x10 more like a Tweed Super and my 5E3 build, well, like a Tweed Deluxe. It would be an easy swap.
     

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