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
    Parts are rollin' in. I'll test the amp (eventually) with JJ's, but for operation afterwards I'll use this Sylvania 6V6GTA with huge black plates. I got this ANOS from KCA NOS tubes.
    IMG_4538.JPG
    IMG_4537.JPG

    And for the rectifier, I've got a RCA 5Y3GT with black plates and labeled "Admiral." This is from Brent Jessee's page on Ebay. He's got some great deals there on used and ANOS tubes.
    IMG_4535.JPG
    IMG_4536.JPG
     
    Last edited: Nov 6, 2017
    Outlaws, Axis29 and King Fan like this.

  2. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Another question, this time about wire: the wire that comes with the Mojotone kit is 22ga solid cloth push-back wire. I have a bunch of 22ga stranded push-back wire coming today. Does it matter which one I use for the leads off the board?
     
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  3. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Oops see next...
     

  4. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    This'll get you some opinions. :)

    Mine: Given the limits above on re-bending solid at a single point (and as noted too, fatiguing stranded in a length you tin) I find solid a ton easier to shape and lay down against the chassis. And I find *that* a big advantage especially in a tweed 'shoebox' chassis.
     
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  5. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    Speaking for myself, I prefer solid hookup wire - stays where its put.
     
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  6. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    Yup, I like the stiff wire too. Either solid or tinned stranded.

    It appeals to my seldom seen neat and tidy side.
     
    King Fan likes this.

  7. D'tar

    D'tar Tele-Holic

    940
    Jan 11, 2013
    WNY
    Seven strands of copper mined from the Isle Royale, tinned with Mines of Laurion silver, tempered with dragons breathe!


    Or Mojo cloth covered push back solid core will do.
     
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  8. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    That 'fable cable' works well for powerful wizards, like, er, Merlin... :)

    The Mojo stuff is fine for sure. You remind me I also really like the stuff Doug Hoffman sells -- IME it's nicely resistant to some repetitive bending.
     
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  9. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    I used to work in a quality lab for a telecommunications company. We tested a lot of materials because some products used in telephone central offices have 10 and 15 year warranties.

    Some of the wire tests we did were called 'Bend and Twist'. Suffice to say, if you break wire by bending it, you have made a couple hundred bends too many. You should grab a new piece and start over. Solid core wire does break more readily if you nick the wire when you strip it. Simply put, don't do that. Readjust your stripper and maybe practice a couple of times. Everything will be just fine.
     
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  10. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    I do have solid-core wire after all. I found that Mojotone sends 22ga yellow, but the green is 18ga. I'm using it because it came with the kit, and because I'm following the color scheme they use. But that 18ga stuff is not nearly as easy to work with!

    I have a question about wiring the leads: I thought I'd wire up the board and then figure out the grounding scheme later. I'm wondering now whether I have to figure out the grounding scheme ahead of time. Here is a picture from the Mojotone 5f2a kit manual of the back of the eyelet board. I don't understand what's going on with the green wire on the bottom left side of this photo. There is a long green lead coming off the bottom right side of the board that corresponds to the top right side of the board when the parts are facing you. So all the "bottom left" green leads in this picture are coming off the filter capacitors and also off the top of the board where the cathode resistor and the 220k resistor and the power tube bypass capacitor meet in that eyelet.

    What I can't tell is whether those bottom five eyelets in the photo (= top five eyelets, counting from the left when the board is faced right-side up) are connected together at points, or whether they're all individual leads going off to who-knows-where. Can anyone enlighten me on this?

    In addition, the photo shows a yellow lead being attached to the first filter capacitor at the bottom (in the photo, it's at the top) and going off into space. But in the layout, there's nothing there [I've posted the layout in the next post].
    5f2a fiberboard leads back.jpg
     
    Last edited: Nov 7, 2017

  11. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Here's the Mojotone layout:
    Mojotone 5f2A Layout.jpg
     

  12. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    Its best to figure out your grounding ahead of time.

    This simple picture of Merlin Blencowe's sums up appropriate grounding for a simple single-ended amp.

    From his chapter on grounding here, which everyone should read.

    http://www.valvewizard.co.uk/Grounding.pdf
     

    Attached Files:

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  13. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    The heaters twisted AC pair can be ground referenced (either with the Heater winding CT, if there is one, or) 2 x 100R reference resistors (one from each side of the winding) attached to an elevated voltage (such as the 6V6 cathode - assuming the 6V6 cathode resistor is fully bypassed).
     

  14. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    The chassis safety ground should be separately grounded with its own dedicated ground attachment point using a ring terminal 1st crimped (and then soldered, and not the other way around) onto the mains earth stranded cable, and then fastened securely to the chassis with its own bolt and locking nut (i.e. a lock tight nut). Again See Merlin's chapter on grounding.
     

  15. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thanks, tubeswell! I'm going to go read up on grounding schemes now. It sure seems to make a whole lot of sense to use a ground omnibus. If I use a bus, what gauge would y'all recommend? I'd need to order them, I guess...
     

  16. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Hey @King Fan - I recall your mentioning @robrob 's grounding scheme. I went to his site and tried to find a discussion, but I didn't locate it. Can you point me to it? Thanks!
     

  17. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    A 5F2a can have a simple ground scheme, kissin' cousin to a 5F1. Look at this great picture courtesy of @robrob :

    5F1_Layout.png

    The black wire labeled 'power amp ground bus' connects the first two filter caps' jumpered negative/ground poles (in your amp this will be the first *3* filter caps jumpered poles, as the first two act as one) plus the power tube cathode/cap grounds to a 'power section' ground point that it shares with any grounds coming off the PT.

    The third filter cap's negative pole and all the other 'ground leads' from the board jump on board the gray 'preamp ground bus'. Note ground connections from the pots also go to this bus. In most small Fenders we build here, in fact, all the grounds except the power section go to this bus, and it in turn has one and only one connection to the chassis, at the input jacks as Rob shows.

    This is the most usual and most useful ground scheme. You can use black wire for the power section ground 'bus', and the preamp bus could be heavy bus wire, tinned bus bar, or even a strand of copper from a chunk of Romex.

    While we're on this drawing, Mojo's layouts are OK but can be 'too vintage' for safety or clarity around power wiring. Tubeswell's separate safety (AC household mains) ground is shown nicely above, as is the safe, standard wiring of hot (black) and neutral (white) wires coming out of your mains power cable.
     
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  18. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    Anything between 14 and 18ga. To straighten lengths of buss wire, put one end firmly in a vice and grip the other end with a pair of pliers while pulling on the wire hard and twisting the wire in one direction about its longitudinal axis.
     

  19. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thanks so much, @King Fan ! Yes, I've been using that 5f1 layout a lot, but I didn't realize that following Rob's grounding scheme simply meant doing it like he does in the graphic! :) Too easy! :) It makes sense that the filter caps have to be jumpered together and then come out of one spot to the bus bar. I'm going to use a bus bar for the power amp and the preamp. That just makes sense to me.
     

  20. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Excellent! Thank you. I could order some of this from Tube Depot, but I should probably just head over to the hardware store across the street tomorrow and see what they have. I like the idea of pulling some copper out of Romex. Very practical and quick.
     

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