5E3 Power Section Numbers....Voltages Etc

Discussion in 'Amp Tech Center' started by DennisM, Feb 28, 2020.

  1. DennisM

    DennisM Tele-Meister

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    Home built 5E3. Was wondering what the ideal B+, Plate voltage, voltage across cathode bypass etc is? What's my goal?

    Here's what I have now:

    Plate=362v
    B+ 1=369v
    B+ 2=336v
    B+ 3=245v
    Across cathode bypass=24.6v
    Cathode resistor=470 ohms

    So, 24.6/470=.052/2=.026A
    .026A x 362v plate = 9.41W dissapation

    Does this look right....are the voltages too high or low? Just checking to see if I'm close to correct tolerances? The amp sounds good with no noise.
     
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  2. dan40

    dan40 Tele-Afflicted

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    You would normally shoot for a dissipation of 12 watts on the 5e3 but it's not a requirement. The standard 250-270 ohm cathode resistor would likely put you right on target. If you are happy with the amp's sound now, you could leave the 470ohm in and call it a day.
     
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  3. dan40

    dan40 Tele-Afflicted

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    Your voltages look good. If you do decide to try the 250 ohm cathode resistor you may see the b+ drop slightly from the extra current draw which is completely normal.
     
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  4. DADGAD

    DADGAD Friend of Leo's

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    With that 470 ohm cathode resistor, you could run a pair of 6K6 pentode outputs. They can be fun.
     
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  5. DennisM

    DennisM Tele-Meister

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    I thought the target was 70%? I'm using JJ 6v6's and they handle 14 watts, so I figured 9.4W was a good figure? I started with a 250 ohm resistor and ended up with something like 13W? What would be the result sound wise of a higher dissipation?
     
  6. dan40

    dan40 Tele-Afflicted

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    70% has become a guideline many use in fixed biased amps. Most cathode biased amps such as your 5e3 tend to run their tubes right at 100% dissipation. Lowering the cathode resistor should make the amp sound a bit dirtier. If you prefer higher headroom from your 5e3 just leave the 470 ohm in place.
     
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  7. DennisM

    DennisM Tele-Meister

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    THANKS!! I wondered why it was so clean! :)
     
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  8. monkeybanana

    monkeybanana Tele-Meister

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    What transformers are you using? I like your numbers :)
     
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  9. cobaltu

    cobaltu Tele-Meister

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    I think you calculation is a bit off. You are supposed to subtract the Cathode voltage drop from the Plate voltage.

    Like this:

    24.6V/470 = .052A/2= .026A

    362-24.6 = 337.4V

    337V * .026A = 8.77W

    I would drop the cathode resistor to ~ 300 ohms.
     
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  10. DennisM

    DennisM Tele-Meister

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    Oh wow. I didn't know that. Stands to reason. I went in an put a 250 ohm in it and it's never sounded this good. Because of my mistaken 70% rule, this thing was was running so cool...didn't sound like what I thought a 5e3 should. Does now! :) I'll measure the numbers in the morning. Thanks to you and all for the help!
     
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  11. DennisM

    DennisM Tele-Meister

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    I got it from Antique Electronic Supply. I heard that they are rebranded Classic Tones, but can't swear to it. It's the one listed on their site for Deluxe, Deluxe Reverb. It's got a 50V bias tap too. I might use this same tranny in a 5f11 build I'm planning.
     
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  12. DennisM

    DennisM Tele-Meister

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    Thank you too @dan40. You helped me a bunch!
     
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  13. monkeybanana

    monkeybanana Tele-Meister

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  14. King Fan

    King Fan Friend of Leo's

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    That's a great 5e3 PT. They're not *rebranded*, exactly: AES just sells the wholesale version from Magnetic Components (MC), ClassicTone's parent firm. Other than the even-more-confusing name scheme, they're the same thing from the same company and factory. CT calls this the 40-18016.

    upload_2020-2-29_10-46-17.png

    EDIT: I'll be interested to see your new numbers. Are you using Rob's bias calculator? It's super easy since you can use his 'cathode resistor voltage drop' method.

    That 330-0-330 may run your JJs right near 100%. If you don't get to 100%, that's OK, but if you're curious, some folks find standard '12W' 6V6s may sound a bit different -- some say better -- and NOS versions may sound better still. Why do I mention it? The 12W tubes often bias out over 100% -- mine have run between 107 and 112% in my 5e3 with that transformer -- but the sturdy old NOS versions at least can do this all day long. I've run 1953 RCAs and 1947 Ken-Rads for years without issue...
     
    Last edited: Feb 29, 2020
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  15. DennisM

    DennisM Tele-Meister

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    I installed the 250 ohm resistor last night. The new plate voltage dropped all the way to 323v. The cathode bias is now 17.6v. The actual resistance on the 250 is 247ohms. The new current is 35.6mA. All this gives me 10.87W dissipation. I might try Tung Sols or some different 12W 6v6's. Can't afford the NOS stuff. I like the way it sounds much better now, but it's still too much amp for an old bedroom picker. The 5f11 vibrolux is looking better and better by the minute :)
     
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  16. King Fan

    King Fan Friend of Leo's

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    The Tung-Sols are said to sound nice if you get a pair that don't die in the early going. See if you can buy from somebody who gives you a 30-day guarantee -- is 'guarantee' a thing on tubes? :)

    If you're looking for bedroom (OK, music room) levels from a 5e3, you can get great bluesy 'tweed cleans' setting the tone at 6 or below, the active volume at 2-4, and the inactive-channel volume at 9-11. Sit to the left of the amp (away from the PT) and try twiddling the knobs some in those areas. Of course you can plug into channel 2, but that's the same as turning down your guitar... which is a great idea on a 5e3. Turn down the guitar volume so soft pick attack gives notes that sound quiet and clean, but digging in can give you rasp and depth.

    If you want tweed *dirt* at home levels, a good attenuator can help.
     
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