1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

6L6 in a Champ 5F1

Discussion in 'Amp Central Station' started by James Knox, Dec 3, 2020.

  1. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    215
    Joined:
    Nov 23, 2020
    Location:
    Finland
    James I recommend you at least test the Universal Loadline Calculagor which Giuseppe Amato has done which you find it in this attached link. It is much faster than draving londlines to datasheets. For cathode bias notice that what the voltage which appears to Grid Bias box you need to add to V+ to have what your B+ in working amplifier needs to be. Grid bias voltage also changes when you change Screen voltage.

    Loadline is biased to balanced and "best "A-class when the Power "at class A/A"-box comes about the same it is "at max g1"-box and it shows green over loadline when you put voltage to "headroom"-box where good starting value is 30V less than V+ becauee anode voltage can not go to zero. Calculator calculates also distortions for the "headroom" you have set and when you try different bias points and look what effects to what?


    https://www.vtadiy.com/loadline-calculators/loadline-calculator/
     
    James Knox likes this.
  2. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    215
    Joined:
    Nov 23, 2020
    Location:
    Finland
    This is 6L6A (without B but 19W tube) loadline which values are in the middle on your lower picture. Bias is not in the middle but for guitar amp it might be better to produce more 2nd harmonics?

    There is difference on G1 voltage and obviously it is because data which is used in calculator is not the same your actual tube is? This vould make cathode resistor need is about 540 ohms but I calculated from your data and obviously you have 470 ohms?

    James I understood yesterday it is also your Harvard build why I did not continue my 1750B single ended build because it was so interesting to read its excellend thread in "Schock Brothers forum" and I wan't one for myself too :)

    PHOTO-2020-12-20-19-33-19.jpg
     
    Last edited: Dec 20, 2020
  3. radiocaster

    radiocaster Poster Extraordinaire

    Posts:
    7,997
    Joined:
    Aug 18, 2015
    Location:
    europe
    On the datasheets, both the JJ and Tung Sol are both listed as 14W. You had mistakenly used 12W for the Tung Sol.

    By 5881, I assume you mean Sovtek. Those have 20.5W max plate dissipation.

    I assume you mean 6P3S by 6L6GB, these:
    https://nesstone.com/product/sovtek-6l6gb-nos-tube/
    Those are not true 6L6s. 20W max power dissipation.

    So really they not all that far off from each other.
     
  4. James Knox

    James Knox Tele-Holic Silver Supporter

    Posts:
    850
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Wow, that Load Line Calc is great! Thanks for the link to it :)
     
  5. James Knox

    James Knox Tele-Holic Silver Supporter

    Posts:
    850
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    I used the 12W for the Tung Sol because I have read that they have a reputation for red plating. I wanted to go conservative on the number. I really like the sound of the TS over the JJ even though JJs seem to be more popular and hardy.

    These are the tubes (5881 and 6L6) I am using. Got them from AES.

    95D4303B-A7FF-47F4-8C3F-90D7041F6BF7.png

    7E3ECD6C-A3B1-42E8-9D74-6F873F030CC4.png
     
    radiocaster likes this.
  6. James Knox

    James Knox Tele-Holic Silver Supporter

    Posts:
    850
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    I have read guys talking about “load lines” buT honestly I have not Under stood or studied them yet. Your bias Calc has me inspired me to delve into the world of “load lines”. Thank you for that!

    Yes, I am using a 470 ohm and would like to not replace it, lol.

    Yes! The Harvard as such a fun build. And I really LOVE the sound of that Amp! My 5F2A Princeton with a 5U4G and a 5881 and my 5F10 Harvard Are my favorite amps. Tone, volume, tactile response - all there for me. I joke with my wife that I am getting an IVY LEAGUE education (Princeton and Harvard, lol)
     
  7. BigDaddy23

    BigDaddy23 Tele-Holic

    Age:
    47
    Posts:
    674
    Joined:
    Jan 4, 2019
    Location:
    Australia
    Hey James - cool project! Have a look at this 2-Stroke/5F2a build thread of mine. I got it using 6V6, 6L6 and EL34’s with success. Killer tone. I sold it to a local muso who wanted it after a jam. Essentially, it works by running the OT at a mismatch impedance to the speaker for the big bottles (ie 4R tap with 8R speaker). I reckon Rob has the logic behind that in his fab site. Maybe that will help you with your conundrum?

    https://www.tdpri.com/threads/5f2a-princeton-2-stroke-build.985746/
     
    James Knox likes this.
  8. James Knox

    James Knox Tele-Holic Silver Supporter

    Posts:
    850
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Cool - thx for the link! I’ll go study it. I’ve read others talking about evening OT things out with the Speaker impedance. I need to learn about that.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.