Pls review my rookie 5F1 kit build...

Discussion in 'Shock Brother's DIY Amps' started by Kws_Brit, Jul 7, 2020.

  1. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Hello,
    I'm retired and have just began my guitar journey in the last year. Am an amateur woodworker so decided that I could build a small amp! With only 26 components how hard could it be? Little did I know!
    I found RobRob's site (Thank you!) and decided on a Mojotone kit. He mentioned that StewMacs instructions were good so am using that also. Who would know that there are so many variables involved, parts, methods, etc.

    After much reading and researching I'm at the point of asking for your review and help. The parts that I have bought are: mojo small parts kit; Classic Tone PT and OT; Weber CVA8 speaker.

    Here are pics and Thanks for comments and help in advance!

    board front.jpg board back.jpg board with attachments1.jpg board with attachments2.jpg board with attachments3.jpg PT leads.jpg OT leads.jpg
     
  2. jhundt

    jhundt Doctor of Teleocity

    Age:
    66
    Posts:
    12,437
    Joined:
    Mar 23, 2003
    Location:
    Netherlands
    I admire your building style! When I built my first amp I was a complete and total novice with zero experience, and little skill, ability, knowledge, or handiness. I was quite worried that I would mess it up, so I read and studied and marked drawings etc, etc. You have taken this approach to a new level, and I mean that in a good way. All the time you have spent here will certainly pay off.

    By the time you get to your third amp, you probably won't even have to look at the schematic anymore!
     
  3. Meteorman

    Meteorman Tele-Holic

    Posts:
    947
    Joined:
    Dec 23, 2012
    Location:
    State College PA
    welcome to the sickness.
    you might consider tightening up your heater wire dress between V1 and V2 before soldering.
    some might comment on your grounding scheme; I think Rob separates preamp bus from power bus, but others don't.
     
  4. Junior Little

    Junior Little Tele-Meister

    Posts:
    230
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    Welcome to the addiction that is tube amp building!
    Just a couple thoughts: twisting the heater wires going to your 6V6 might reduce the possibility of hum. And some folks like to put a bypass cap (25uF at 50V) across the 1.5K resistor coming off of pin 3 of the 12AX7.
    Have fun!!
     
  5. Jesco

    Jesco TDPRI Member

    Age:
    41
    Posts:
    46
    Joined:
    Feb 16, 2017
    Location:
    Oakland
    It looks like you have added an artificial center tap. The easiest way to deal with those resistors is to hook them up to the cathode of the 6V6 to create elevated heaters. Kills two birds with one stone. Just run the 100k artificial center tap resistors from pins 2 and 7 of the 6V6 to pin 8 of the 6V6.

    Elevated heaters may be overkill in such a small amp, but it’s easy.
     
  6. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    JHUNDT: Thx for reviewing, appreciate it!
     
  7. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    METEORMAN: Thx for comment, I'm waiting on some 18ga cloth wire so will definitely tighten those up.
     
  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    4,180
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    You actually don't need the artificial center tap at all since you have the green/yellow wire on the power transformer.
     
  9. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Hey JESCO, Thx for reviewing. I'm barely a rookie at this so dumb questions are in order and here goes!

    What I know about center taps is that I do have two coming off the PT and both will be grounded. Green/Yellow to PT ground bolt, and the Red/Yellow will be connected to the power amp ground bus which will then go to the same PT ground bolt.

    I'm assuming that the "artificial center tap" you mention are the two resistors attached to the light and that will be grounded thru the light to the chassis, and from there the green power goes to the 6v6 to pins 2 & 7. Is that correct?
    (Mojo has these as well as other kits I've seen..., but no CT's from PT)
    So, are these the two resisters you're talking about? And would I even need these 2 resistors?
    (If I'm way off track pls redirect me! Ha!) (And, I have no idea what these are even for...)

    Thanks for your help!
     
  10. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Hi Junior, Thx for reviewing!
    OK, now I see that on RobRob's picture. Mojo does not have it and no mention is made.
    What is it for and is it highly recommended? i.e., does it better the sound?, or what?
    Thx again!
     
  11. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Corliss1, Thx for reviewing and comments.
    Yes, I just asked Jesco that very question (I think..., if I did truly understand the resistors he was referring too). Thx, omitting those w/b much easier!
     
  12. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    4,180
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    Depending on which champ schematic you look at, that cap isn't there.

    The cap will increase gain on that preamp stage, which is usually what people are looking for in a champ. All the vintages ones would have had that part included.
     
    Junior Little likes this.
  13. Junior Little

    Junior Little Tele-Meister

    Posts:
    230
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    See what @corliss1 said in post #12 above...
     
  14. andrewRneumann

    andrewRneumann Tele-Meister

    Posts:
    256
    Joined:
    Mar 22, 2020
    Location:
    Cincinnati, OH, USA
    You might consider building the amp without the 25uF first stage cathode bypass cap and then test the amp with it connected using only alligator clips. That way you can test with/without and choose what you like without having to unsolder.

    Make sure you are familiar with safely unplugging the amp and discharging the supply caps before doing any work like this though.

    Edit: And welcome to this great hobby and excellent forum!
     
    Kevin Wolfe likes this.
  15. Tom Kamphuys

    Tom Kamphuys Tele-Meister

    Age:
    40
    Posts:
    439
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    @Junior Little, this is how you can answer to someone. They receive a notification that way.

    Have you found the website of Valvewizard? It has high quality information, also about stuff that is mentioned above.
     
  16. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,277
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    What @corliss1 said, of course...

    More generally, I like Mojo and have built their kits, but their drawings always need a cross-check, first against the Fender original (though IIRC Fender didn't show that cap, which they were actually adding on the shop floor) and especially against a gold standard, which *as you've figured out* for the 5F1 may well be Rob's version.

    You're doing a good job. Keep up the research -- and keep asking questions!

    Check especially the power wiring and ground scheme.

    5F1_Layout.png
     
  17. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Corliss! and Junior,
    Thx for info! I will need to order another Sprague 25uf @ 50V cap. (one came with Mojo kit...used it with the 5W 500ohm Xicon resistor).
     
  18. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Hey @Tom Kamphuys,
    Thx for info on Valvewizard website. Will definitely access their info!

    Now, about this replying with notifications...., it isn't readily apparent to me how you do that! Can you explain?
    Thx for your help!
     
  19. Kws_Brit

    Kws_Brit TDPRI Member

    Age:
    70
    Posts:
    15
    Joined:
    Jul 7, 2020
    Location:
    Mpls, MN 55112
    Hello @King Fan,
    Thx for info.
    And yes, the power and grounding are somewhat confusing.

    I just have a bare metal jumper between the eyelets for C3 and C4, with a green 18ga wire going from C3 to the PT ground bolt. Also here there will be red/yellow HV Center Tap wire connecting to the C3 eyelet.
    On the preamp ground, on the backside I have another green 18ga wire connecting the top C5 eyelet and the far right front top eyelet. Both ends appear to me to be going to ground, one from the POT and the other to the ground tab on the #2 low Input Jack.

    The power wiring I think I have figured out. But still have some hesitation as to what exact connections to use on the fuse and POT. The end fuse tab s/ get the power cable black, and the side tab s/ then be connected to the top POT tab, with the PT black cord then connected to the bottom POT tab. That is what believe is correct. Thx again.
     
  20. Junior Little

    Junior Little Tele-Meister

    Posts:
    230
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    When you hit the "Reply" button the quote is inserted for you, apparently. Using an @ symbol immediately followed by the username is how you call out someone specifically without directly quoting them.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.