Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

New (and first) build: 5f2a Tweed Princeton

Discussion in 'Shock Brother's DIY Amps' started by theprofessor, Nov 2, 2017.

  1. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Ah --- electrically shorted! Well that makes sense! And, yes, I did that too! I'll take that jumper off now and re-post! Thanks for putting up with my thick-headedness when it comes to this stuff! You too, @FenderLover !
    I'm reminding myself of this:

     
    Last edited: Nov 9, 2017

  2. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Ok, here we go: voilà!
    IMG_9483.JPG
     
    Nickadermis and King Fan like this.

  3. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Now that I've got those new voltage-dropping resistors in, this is the best I've got before putting it in the chassis. Calling all experts: everything look okay? I'm going to attach the two black wires at the top right to the preamp bus bar.

    board_FINAL_front.JPG board_FINAL_back.JPG
     
    Last edited: Nov 9, 2017

  4. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    Grounding suggestion following logic in Merlin's article. Keeps the pre-amp filter cap ground with the pre-amp ground returns going straight to the input jack, and also has the other filter caps and output tube ground return going straight to the input jack. YMMV
     

    Attached Files:

    Axis29 likes this.

  5. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thank you, @tubeswell, for taking the time to make these detailed comments on the photo! I'm sorry some of those leads were criss-crossed. A few minutes ago, I changed one of the top leads, since it seemed to be different than the Weber layout. The pictures in the post immediately above are different than the one you edited, in that one of the black leads has been moved from the preamp filter capacitor to the eyelet where the cathode resistor and cathode bypass cap are. My problem at this point is not having enough knowledge of the steps ahead of me, especially the grounding scheme.

    I'll go read Merlin's chapter carefully and then come back to your very helpful description of a suggested grounding scheme and see if I can repeat it back to you intelligently. Thanks so much!
     

  6. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    Otherwise use a simple buss bar and copy the grounding diagram from Merlin's article that I attached in that earlier post.
     

  7. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thank you!
     

  8. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    This thing better be singing before Thanksgiving....;)
     

  9. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Man, I hope so! I'm pretty well set to put in this board (provided that it looks ok to you now; does it?) and start wiring things up. But I'm also learning as I go and now need to give attention to understanding a good grounding scheme. I can copy pictures with the best of them, but I'd like to understand as much as possible as well. Cheers!
     

  10. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    Looks fine to me - carry on!
     

  11. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Some motivation for you:

    A local musician came over tonight for some tube amp advice. He also wanted to test run a few of my amps. Compare sizes, speakers, circuits etc. He was floored by the 5F2A. He took it home...For a week. I let him borrow it.

    You’re gonna love it too!
     
    Last edited: Nov 10, 2017

  12. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thanks for the encouragement, Keith! I'm really excited about it. I still have a bit to do, but I'm getting closer...
     

  13. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Professor, your board looks good.

    The split ground bus is the way most people do their amps these days but this is what Merlin and most electrical engineers would say is a "better" way to do it. One ground bus with the output transformer center tap connected on one end (with no ground connection) and the only chassis ground at the input jack on the other end. Here' a 5E3 layout with a single bus bar:

    [​IMG]

    With a split ground bus the returning current from the preamp has to flow through the chassis to get back to the power transformer center tap. With a single bus no chassis current flows--all returning current flows down the bus bar.
     
    King Fan likes this.

  14. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks, Rob, I've always wondered about that. Not knowing EE, I find Merlin pretty clear and convincing -- with the former aiding the latter. :) BTW I think that's why your site is so popular -- you explain why things are the way they are and you do it in terms we can understand.

    So 'better' aside, what's your take on how to *most usefully* ground amps like Prof's 5f2a and amps in the neighborhood with few gain sectors and limited chassis space?

    I ask 'cuz I've read that advanced ground schemes are most useful and needed in 'big' amps, and that simple, 'imperfect' ground schemes can be 'just fine' in the small amps that many of us build. I've used what I call "Rob's 5e3 scheme" -- split grounds -- on amps up through my AA1164 with 'perfect' results. Can we assume if you thought the scheme above was actually better, you'd publish it on your 5e3 page?
     

  15. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thanks very much, @robrob! At this point, I'm thinking of what I believe you're saying is the split ground bus, one being for signal ground, the other being for power ground.

    It seems to me that it would be very easy to connect B+3 and all the way back to input 2 using a simple bus. Working left to right, I can connect the .0047 Orange cap coming off the tone pot --> the B+3 preamp filter capacitor --> the ground lug of the volume pot --> the eyelet where the 220k resistor, the 25μF coupling cap, and the 470ohm cathode resistor meet --> the V1a bypass cap and V1a cathode resistor --> all into the ground lug of input 2. Is that correct? And input 1 doesn't get attached to the bus?

    If so, what I've got to figure out then is where the ground for the power amp filter section goes...
     

  16. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Edit
     

    Attached Files:

    Last edited: Nov 10, 2017

  17. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    In Merlins ground buss method, the OT Primary winding's B+ lead connects to the +ve pole of the (parallel) reservoir capacitor(s), and the other end of the winding connects to the negative pole (of the same reservoir capacitor(s)), which is sitting on the floating end of the ground buss. The ground side of the screen supply node filter cap and the 6V6 cathode resistor both connect to this same point. Everything other ground return (including the pre-amp filter cap ground lead) connects as close as possible together at the other end of the buss bar, near to where the buss bar connects to the chassis at the input jack.
     

  18. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    I use the Fender layout for many things, but regarding grounds
    • The '50s power section is all wrong -- see Rob's drawings instead
    • For one thing, there's no ground or 'death cap' off the fuse any more -- see Rob's drawings
    • It doesn't show the separate safety ground we talked about yesterday -- which is critical
    • The heaters back then were single strand, so the ground location on the 6V6 is wrong, and there's no ground on the preamp tube.
    • They don't show a center tap off the PT, and you will have one -- it needs grounding
    • That leaves two ground arrows going up off the board and two coming down off the pots
    Pending advice from people who actually know something, :D my approach and that of many folks here is to run the ground off the first filter caps to the same point you run the PT center tap -- often a PT bolt with the serrated washer, crimp ring, keps nut, loctite security from yesterday.

    Then the other board ground and the two pot grounds drop to the 'preamp bus' which is anchored once and only once to the chassis at an input jack.

    Does that make sense? Pros, did I 'splain that correctly?
     

  19. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thanks, @KingFan! Yes, that makes sense to me.
     

  20. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Here's what I *think* I know and what I'm sure I don't know, despite everyone's best attempts at getting it through to me. :)

    (1) The Mojotone layout and kit comes with the .047μF death capacitor to hook up to the fuse, just like the olden days. That is dumb. I should toss it.
    (2) I'm working on keeping the signal ground and the power ground separate. So I've gone with a preamp bus bar that reaches, essentially, from the preamp filter capacitor (B+3) all the way to the ground lug of input 2. As far as I can tell now, this bus bar will have four things connected to it, beside the connection at the ground lug of input 2: (a) the .0047 Orange Drop coming off the tone pot (b) the ground lug of the volume pot (c) the ground-side of B+3 and everything that's attached in that eyelet or jumpered to it (4) the V1A bypass capacitor and the V1A cathode resistor.
    (3) The earth ground of the power cord (green) is a part of the safety ground on the left side of the chassis, with its own dedicated connection that is as strong as strong can be. The center tap of the power transformer is also connected there.

    So, questions:

    (1) re: (2) above: Is there something else that attaches to this bus bar, such as the ground lug of input 1? Or is that already connected via input 2, since input 1 is connected to input 2?
    (2) The other big highlighted portion you'll see is the eyelet for the ground side of B+1 and B+2. Where does this go? (sorry, @tubeswell, I know you addressed this above, but I'm so thick on this that I can't tell if you addressed it according to the scheme I'm hoping to use)
    (3) Are the two 100k resistors on the pilot light simply grounded locally to the metal on the light assembly?

    201711101203.jpg
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.