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5E3 Build w/ B+ Gone Awry

Discussion in 'Shock Brother's DIY Amps' started by Huddy, Nov 1, 2020.

  1. dan40

    dan40 Friend of Leo's

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    Keep in mind that the variac test may not give a true indication of the final sound if the heater voltage got to low. Low heater voltage will prevent the tubes from working properly and developing their full gain. The amp may have sounded a bit browner and fuzzier with lower heater voltage.
     
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  2. Huddy

    Huddy Tele-Holic

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    Yes, I was pretty sure that such low heater voltage would have an adverse affect. Though I wasn't sure what it was sound, inaccurate bias readings, or both. But the goal was see if I could it in the bias ballpark.

    Really crossing my fingers on these 5Y3s I've got coming.
     
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  3. JamesAM

    JamesAM Tele-Meister

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    I had the TAD 5y3, and I can say it is essentially a 5v4 (ymmv as always). my voltages were way too high with that rectifier in my 5e3. A JJ or NOS will drop your voltages to more reasonable levels.

    I had to bite the bullet and get a NOS Raytheon to get my voltages in the neighborhood of normal. I also had to mess with bias resistors to get to a decent plate voltage and b+. However, I also have a deluxe reverb output transformer, whose 6.6k ohm primary makes things a bit hotter anyway.

    My guess is you will have to do the same experimentation as I did with your cathode resistor, as your PT is hotter than mine. You may want to order a few different ones now (anywhere from 270r to 470r given your PT and its voltages to the rectifier) if you want to prevent another wait as with your rectifier tubes.

    just a suggestion, and imho only. Be careful and have fun!
     
    Last edited: Nov 8, 2020
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  4. Huddy

    Huddy Tele-Holic

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    NEW TO ME 5Y3 UPDATE -

    I got my box of a few 5Y3s pulls... Just and a second to do one of them... a Sylvania

    Wall voltage - 121 AC
    HT Secondary - 370-0-370 AC
    B+ - 384 DC
    Plates - 377.5
    Cathode - 21.5

    Here's the Rob's chart w/ JJ 6V6s selected.


    Screen Shot 2020-11-09 at 12.47.27 PM.png

    I'll try out the other two 5Y3s later when I have time but I have a feeling if they'll be in the same ballpark or higher. I did get my volume back. My Preamp and PI tubes are still getting voltages that are a bit too high - (from memory) 190 on the plates of the first 3 triodes and 230 on the PI triode.
     
  5. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    So your plate-to-cathode voltage is 356, and you're at 106% dissipation? :)

    What *is* your bias target? And remind us, what size bias resistor are your running right now?

    This is about when folks start to ask for a full new voltage chart...
     

    Attached Files:

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  6. Huddy

    Huddy Tele-Holic

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    bias target? I’m new to scratch builds so I don’t have a set number - previous target was “don’t eat up power tubes”. Now that I’m out of that territory I’m open to suggestions.

    I’ll definitely get a full chart together this evening when I have time to really focus on it and be super accurate with everything.
     
  7. Huddy

    Huddy Tele-Holic

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    right now I’ve got 250 ohm 5 watt that meters a 244.7 ohms.
     
  8. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    With JJ 6V6s, you could just consider yourself done. The amp will act as any 5E3 does with high B+, but none of the components are in danger. :)
     
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  9. JamesAM

    JamesAM Tele-Meister

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    Look forward to your voltage chart- im interested in seeing yours compared to mine to compare power transformers!

    As others have said, if you like the sound of JJs, you can probably say you’re done and go play that bad boy. If you prefer a smoother breakup, you can go with another 6v6 and see how your voltages look.

    if they’re still high or you redplate, you can up the bias resistor value. You have plenty of room on your plate voltages. I bet a 270 or 300r will get you where you need to be. Alternatively, you could go the zener diode route to lower the voltages from the PT.
     
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  10. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    For what it's worth, I think people who want to build a 5E3 would be better off getting a power transformer spec'd for a Deluxe Reverb, like the Hammond 290BX. The mounting bolts have the same spacing, but the secondary voltage is lower (generally 640-680VAC). With a DR PT, your voltages are bound to end up in the right zone to make your tubes happy in this application.

    All of those 700VAC+ "tweed Deluxe" PTs just set people up to have the same issues with high B+, and then they have to feel frustrated and apply band-aids to make things work out, when they shouldn't have to! Sorry, this is a pet peeve of mine...
     
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  11. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    So folks are saying you already hit the target. Dissipation is the key value, and 105-110% is an excellent goal, so unless your full voltage table is way out, you’re done. Good job!
     
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  12. Huddy

    Huddy Tele-Holic

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    Yup - I totally agree. But... Excellent learning experience for me so far so I'll take it. ;)
     
  13. Huddy

    Huddy Tele-Holic

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    Alright - So here's my voltage chart. I've got my wall voltage. My HT w/ the 5Y3 installed... B+ and all relevant tube pins.

    I have two V1 and V2 readings because one has a 12AY7 in V1 and the other with a 12AX7 in V1. V2 remained constant as the 12AX7. Note on the 12AX7 in V1... It appears to be unbalanced? I had another one in there yesterday or the day before but it's in a different amp and didn't have time to dig the original one out of another amp I had it in or find another one. The original 12AX7 that I had in V1 had more balanced-ish voltages and that were all but spot on w/ V2A.

    The 12AY7 brings all the voltages down for V2 as well. I don't know if that's normal or not. I've tried two different 12AY7s and they both were around 140v compared to the 190 of the previous 12AX7.

    I won't be in front of the amp for a few days so I won't be able to make any tweaks until Friday probably.

    Also the Output tube's plate dissipation is just the cathode method a la uncle doug.

    Screen Shot 2020-11-10 at 5.37.59 PM.png

    Lemme know your thoughts! Thanks so much!
     
  14. dan40

    dan40 Friend of Leo's

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    Since the preamp tubes are usually set up in cathode bias, the 12ay7 is operating at a different bias point than your 12ax7 was. It is likely drawing a bit more current through the 22k preamp dropping resistor so all of your voltages on v1 and v2 will fall slightly. You will notice slight differences in the plate voltage readings of almost every preamp tube you install.
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The 6V6 bias calculation does not subtract the screen current. Rob subtracts an estimated 5.5% screen current when using his bias calculator.
    If you subtracted an estimated 5.5% screen current the result would be a Plate dissipation of about 14.4 watts or 103% per tube.
     
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  16. Huddy

    Huddy Tele-Holic

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    Yes I just used to the same google doc and that simple cathode method was already there and calculated the figures I plugged in.
     
    Last edited: Nov 10, 2020
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  17. JamesAM

    JamesAM Tele-Meister

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    I would be less worried about preamp voltages and more on getting the bias to where you want it to be. As @King Fan said, what is your bias target? I keep coming back to your plate-cathode voltage of ~355 and a b+ of 43mA/tube. My calculations match @Lowerleftcoast with 103% for a 14w tube taking into account -5.5% grid current.

    if you like the sound of JJs, play it- if you don’t, get some different 6v6s and see if you need to rebias. If dissipation is too high for those tubes, experiment with cathode resistors to lower that b+ current. Your plate voltage may increase, but you have some room to spare. If your target is below 100% dissipation, as others have alluded, that may not be possible with your PT- at least not without changes to the circuit or lowering voltage from the PT with diodes.
     
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  18. Huddy

    Huddy Tele-Holic

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    Yeah honestly - I was very pleased for the hour I played it with the new rectifiers. Previously it seemed a bit louder and wouldn't break up unless dime'd. Now if the volume is a little past "noon" it's pretty responsive to pick-attack, which I like. So I'll probably leave it as is until I have something else to compare it to and get a little bit more experience under my belt. Does it sound like a legit 5E3? Doubt it. But I wouldn't know cause I've never heard a real one in person. Very happy regardless. Thanks for the input!
     
  19. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Good for you. If it sounds good and biases at 100-115%, what makes you think it doesn't sound like a 'real' 5E3? I'm thinking it likely does! :)

    BTW, you may *not* be limited to running JJs -- Rob, based on both data sheets and lots of user experience, re-classified the 6V6GT as a 14W tube. I wouldn't try it out on new-issue TS, but my 1947 Ken-Rads and some new-make EH are very happy around 115% dissipation if I calculate them as 12W tubes...
     
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  20. Huddy

    Huddy Tele-Holic

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    Thanks! Just my expect the worst and hope for the best mindset.

    yes I’ve been doing some research on alternatives as a lot of people have said that the TungSols aren’t terribly interested it working too hard. Unfortunately everybody just says JJs I think because they seem to be bullet proof. But I’ll grab a set of EH tomorrow so they’ll be to me by the weekend. Thanks! I’ll grab some different cathode resistors as well incase things get out of whack with them in there.
     
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