6V6 Tube Advice for 5F1?

Discussion in 'Shock Brother's DIY Amps' started by PorkChopExpress, Jun 27, 2020.

  1. PorkChopExpress

    PorkChopExpress TDPRI Member

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    Trying to zero in on a tube for my Boothill 5F1. I originally stuck a 12W Tung Sol 6V6GT in there - it sounded really good but was red plating like a mother (see photo).

    After doing some calculations, I found the max plate dissipation % to be around 115%. So I swapped out the Tung Sol for a JJ 6V6S (rated at 14W), thinking it might get me closer to 100% max dissipation. The JJ tube got me to about 103%, but it doesn’t sound nearly as good. There are some abrasive high frequencies that occur once the tube starts to break; they’re really noticeable at about the 9 or 10 mark on the volume control. I’ve never used a JJ 6V6S before, so not sure if this is normal.

    Looking for some advice on what to do next. Should I put the Tung Sol back in and swap out the power tube resistor with a larger value? Would it help to add a resistor to lower the voltage between the rectifier and B+ connection? Should I try a different power tube? Different rectifier tube (currently using a JJ 5Y3S)? Maybe there is something wrong with the JJ 6V6S tube?

    I can post voltage readings for both the Tung Sol and JJ tube pins if that is helpful. Thanks for any advice!

    729628FF-39B5-4D6D-A611-6768FF2087C8.jpeg
     
  2. Dacious

    Dacious Poster Extraordinaire

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    What's your cathode resistor value? You haven't got the bypass cap in backwards?
     
  3. Tele Slacker

    Tele Slacker Tele-Meister Silver Supporter

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    Yeah, I think the voltages would help the forum offer some better advice.
     
  4. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    And...what's wrong with 115% in a Champ? The only rules for a Champ are:

    1 - does it sound good?
    2 - does the tube redplate in that amp?

    If your answers are yes/no, respectively, rock it out.
     
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  5. PorkChopExpress

    PorkChopExpress TDPRI Member

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    I love this formula, but unfortunately the answer to both questions is yes. Not sure if the photo went through on my first post, but it shows significant red plating with the Tung Sol.

    I’ll get those voltages posted once I get back to my garage
     
  6. tubedood

    tubedood Tele-Meister

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    I went with a nice Sylvania black plate 6V6GT VT-107 from a reputable tube vendor. I like it a lot.
     
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  7. Dacious

    Dacious Poster Extraordinaire

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    Bear in mind there's 6V6s and 6V6s. You may have a high current draw tube due to manufacturing variation.

    But - check orientation of cathode bypass cap. If you have it wrong you'll get redplating.
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Oooooh I see the photo now.

    You can order tubes from vendors and say "hey, this is going in a champ" and they'll get you some that draw more or less current depending on the application.
     
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  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    What power transformer and what cathode resistor value?

    Sent from my moto g(6) using Tapatalk
     
  10. Jesco

    Jesco TDPRI Member

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    I would keep the Tung-sol and get the plate dissipation sorted out.

    As others have said: voltage readings and cathode size on the power tube would help.
     
  11. PorkChopExpress

    PorkChopExpress TDPRI Member

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    Thanks everyone, here are the numbers. I plugged them into Rob's calculator to get more accurate readings than my quick calculations. Hopefully I did this right:

    PT is a ClassicTone 40-18019
    V2 Cathode Resistor measured at 460 ohms (rated at 470 ohms)
    Wall AC voltage = 121.2 VAC

    Rectifier 5Y3S
    PIN 4 = 333.4 VAC
    PIN 6 = 334.0 VAC

    12AX7
    PIN 1 = 179.8 VDC
    PIN 3 = 1.35 VDC
    PIN 6 = 176.7 VDC

    Tung Sol 6V6GT (12W Max):

    B+1 = 372.1 VDC
    B+2 = 311.4 VDC
    B+3 = 204.8 VDC

    PIN 2 = 3.36 VAC
    PIN 3 = 363.8 VDC
    PIN 4 = 315.1 VDC
    PIN 5 = 127.4 mV
    PIN 7 = 3.37 VAC
    PIN 8 = 20.35 VDC

    https://robrobinette.com/Tube_Bias_Calculator.htm
    Tube Dissipation Using Cathode Resistor Voltage Drop Plate Dissipation = 14.4W = 120%

    JJ 6V6S (14W Max):

    B+1 = 378.2 VDC
    B+2 = 330.7 VDC
    B+3 = 287.3 VDC

    PIN 2 = 3.36 VAC
    PIN 3 = 364.0 VDC
    PIN 4 = 332.0 VDC
    PIN 5 = 87.8 mV (reading was not stable - continued to decrease)
    PIN 7 = 3.37 VAC
    PIN 8 = 20.67 VDC

    Tube Dissipation Using Cathode Resistor Voltage Drop Plate Dissipation = 14.6W = 104.3%
     
    Last edited: Jun 28, 2020
  12. Tele Slacker

    Tele Slacker Tele-Meister Silver Supporter

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    What was voltage drop across cathode resistor?
     
  13. PorkChopExpress

    PorkChopExpress TDPRI Member

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    I was using the cathode pin to ground measurement of 20.67 VDC (Pin 8)
     
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  14. PorkChopExpress

    PorkChopExpress TDPRI Member

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    I just had a look to make sure - it's correct
     
  15. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Is it a new speaker? If it isn't broken in yet the JJ might not be the whole problem.

    Sent from my moto g(6) using Tapatalk
     
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  16. PorkChopExpress

    PorkChopExpress TDPRI Member

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    Yes, it is a new speaker. Nothing special (Jensen C8R 4 ohm). Didn't think about that...
     
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  17. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Used it before. You've got about 25-30 hours of straight abuse to START settling that speaker. I like it for what it is, but crank the most bass heavy tracks you have through it as loud as you can stand it for a week or two. Put it in a closet if you have to. They aren't bad, but take a good beating to get there.

    Sent from my moto g(6) using Tapatalk
     
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  18. elpico

    elpico Tele-Holic

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    Don't change the cathode resistor, that biases it off center and is really just a bandaid. Address the real problem which is that all the voltages are too high. If you do this you'll bring both the B+ and the filament voltages back down and that will extend the life of your tubes significantly.
     
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  19. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    You may be able to lower the plate to cathode voltage by using an old 5y3. This would lower the plate dissipation by a little. Many times a new production 5y3 delivers higher voltage than an old version 5y3.

    Perhaps this tung sol is a little week for your 5f1 and a different tube would work with these voltages and bias resistor. (By the way check the actual resistance of the bias resistor. It may be low.)
    Edit: I see your post "Cathode Resistor measured at 460 ohms".
     
    Last edited: Jun 28, 2020
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  20. Nickfl

    Nickfl Tele-Afflicted

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    There is another thread recently where something was having exactly the same problem in a 5e3, they had a pair of new production tung sols that were red plating but sounded good and a pair of JJ's that were working fine but didn't sound great.

    The consensus was that those tung sols are just delicate tubes and often can't handle the hot bias on these amps. I would bet that basically any other new production or vintage tube would be fine. The JJs are another case entirely and theyre known to handle extremes of voltage and dissipation. They may in fact not sound as good because they're not being pushed as hard.

    You have many options, but my preference would be just to get a radio pull/anos 6v6 (or a few of them) off eBay. Or if you're the kind of person that would rather spend money than take your chances on that you can get a true NOS tube from a dealer. Either way US production 6v6 are still a good value and they will probably be your best bet for sounding good and being robust in this amp.
     
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