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.

5F1 Champ - Weber Kit Build/Review

Discussion in 'Shock Brother's DIY Amps' started by jvande7, Oct 6, 2020.

  1. jvande7

    jvande7 TDPRI Member

    Posts:
    94
    Joined:
    Jul 27, 2010
    Location:
    Oakland, CA
    UPDATE: This has less to do with Weber vs Mojo/others etc, and more to do with fine-tuning the 5F1 build/project itself.

    I calculated that my 6V6 was biased quite hot, and even though this is widely accepted nowadays in these single-ended Class-A Champ builds, I used four 5w 9v zener diodes on the PT CT ground to lower my B+ from 383v down to 350v and I like the results. Slightly less output, and slightly "better" overdrive/distortion. Now my 6V6 appears to be dissipating more like 12w instead of 14w+ based on some fast/loose calculations.

    IMG_3004.JPG IMG_3003.JPG


    Next I'm tinkering with the cathode bypass cap value on V1a, as well as choice of preamp tube. Currently using 10uf cap and a 5751 tube for a slightly more mellow/refined Champ, but I'll probably end up with NOS 12AX7 back in there down the road, as I want more of that classic Champ dirt. Just trying to dial out that boomy/farty parts a little bit. Might try a 4.7uf bypass cap next.
     
    Linkjr likes this.
  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,256
    Joined:
    Dec 30, 2019
    Location:
    california
    I think you should adjust for a dissipation of 14w+ for the Champ goodness.
     
    jvande7 likes this.
  3. jvande7

    jvande7 TDPRI Member

    Posts:
    94
    Joined:
    Jul 27, 2010
    Location:
    Oakland, CA
    Only problem is I'm not sure I'm calculating correctly. I'm just a tinkerer, no formal training, and I've found several methods of calculating. Anyone care to chime in as to what I'm actually running here?

    NOS 6V6 (KEN-RAD)
    2: 3.36v
    3: 321v
    4: 303v
    7: 3.38v
    8: 18.25v

    470 ohm resistor (464 ohm actual)

    B+1 352v
     
  4. jvande7

    jvande7 TDPRI Member

    Posts:
    94
    Joined:
    Jul 27, 2010
    Location:
    Oakland, CA
    Original voltages before zener diode mod were as follows...

    6V6

    2: 3.4v
    3: 356.5v
    4: 330v
    7: 3.4v
    8: 20.3v

    same 464 ohm resistor

    B+1 383v
     
  5. Cali Dude

    Cali Dude Tele-Afflicted

    Age:
    58
    Posts:
    1,238
    Joined:
    May 20, 2020
    Location:
    California
    Very cool. I have great respect for you, and guys like you who have the talent and patience to complete such a project. Congrats on the nice finished product.
     
    jvande7 likes this.
  6. El Tele Lobo

    El Tele Lobo Poster Extraordinaire

    Posts:
    6,375
    Joined:
    Oct 21, 2014
    Location:
    Florida
    Agree. Especially with an efficient 12" speaker. I had one built by Modern Sound Amps a few years ago and it's my all-time favorite amp. VERY versatile. I went with a ceramic speaker as I was more interested in tube breakup than speaker breakup. It gives me plenty of clean headroom and roars when cranked. My builder put a switch in it that gives me the traditional early breakup or a higher clean headroom. I use it for everything from country, rockabilly and blues to worship to ambient and jazz. Fantastic amp with a tele!
     
    jman72 and jvande7 like this.
  7. archetype

    archetype Fiend of Leo's

    Posts:
    5,739
    Joined:
    Jun 4, 2005
    Location:
    Williamsville NY
    CJ is awesome. He's a Weber encyclopedia and advice producer.
     
    jvande7 likes this.
  8. jvande7

    jvande7 TDPRI Member

    Posts:
    94
    Joined:
    Jul 27, 2010
    Location:
    Oakland, CA
    Using the calculation method from this post https://www.tdpri.com/threads/5f1-6v6-bias.941913/#post-9019530

    My build/6V6 was originally dissipating 13.82w which is 115%
    and now it's at 11.19w which is 93.25%

    Maybe I'll "remove" one or two of those zener diodes by simply changing where the PT CT wire connects. See how that sounds.

    IMG_3004.JPG
     
  9. Nickfl

    Nickfl Friend of Leo's

    Posts:
    2,538
    Joined:
    May 24, 2016
    Location:
    Florida
    Your calculations look like they're right to me, but the 6v6 is not necessarily a 12 watt tube. Data sheets may list it as such but most people these days seem to agree that they really are 14 watt tubes with the possible exception of the current production tungsols which seem to be uncommonly fragile, and JJ 6v6 tubes which are structurally different and definitely capable of dissipating a good bit more than other makes.

    I think your original plate dissipation was probably about right although the voltages were maybe a bit higher than ideal. At the end of the day what really matters is which sounds better to you.
     
    jvande7 likes this.
  10. jvande7

    jvande7 TDPRI Member

    Posts:
    94
    Joined:
    Jul 27, 2010
    Location:
    Oakland, CA
    Would it make more sense to change the value of the 470ohm cathode resistor on the 6V6? Most folks that have changed that value ended up changing it back to 470 (from all I've read in these forums).

    I'm probably obsessing over nothing and should have just left well enough alone haha
     
  11. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,256
    Joined:
    Dec 30, 2019
    Location:
    california
    ^^^^
    What Nickfl said.

    Your observations of the lower B+ ended up with a more pleasing sound. I would try clipping in) paralleling a resistor with the 470R to see if a lower value cathode bias resistance will work. Of course you can clip a jumper across a diode or two to hear what that does as well.

    I agree with the 14W 6V6 rating.
     
    jvande7 likes this.
  12. Linkjr

    Linkjr Tele-Meister

    Age:
    51
    Posts:
    184
    Joined:
    Aug 16, 2017
    Location:
    Uk
    I also lowered my 5f1 high B+ using zener diodes and the improvement is immense I kept the 470ohm resistor in

    My admittedly limited understanding is people change them to bias a hot tube due to too high b+ but since your voltages are reduced the 470 stock is fine.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.