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Outcaster's solder by number 5E3

Discussion in 'Shock Brother's DIY Amps' started by Outcaster, Dec 7, 2014.

  1. Outcaster

    Outcaster Tele-Holic

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    Lurking here invariably results in a first amp build... Here's mine.
    I threw a low bid at an abandoned 5E3 project on ebay a couple months back and won it. It's most of Mojotone small parts kit, their chassis and Classictone 40-18021 and 18022 transformers.
    The board had already been done and by my eye, looks to be correct. I did reflow a couple of bad looking joints. Still a few changes to make as I'm going to use a ground bus and have to split the pre-amp filter cap from the other two as their grounds are still tied together.
    I'm also planning on doing Robrob's switchable negative feedback mod so I'll add that change to the board before installing it.
     

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  2. Outcaster

    Outcaster Tele-Holic

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    And here's the progress on the chassis from yesterday. Rectifier wired up and heater wiring mostly done.
    One question on that - I've got v1 and v2 pins 4-5 supplied by the same wire that's on v3 and v4's pin 2. Is that still in phase? The Ceriatone layout and a couple of the builds I looked at after have the pre-amp pins 4-5 on the same wire that's on the output tubes pin7.
    If that's okay, then at this stage the only mistake I made was bending over pin 1 to mark it and then soldering the heater wires on the power tubes to...
    Yup, pin 1. I fixed it:oops:
     

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  3. SacDAve

    SacDAve Poster Extraordinaire

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    I just did the switchable negative feedback mod on both mine well worth it. I also from Robs page did the Rectifier Backu Diodes & Phase Inverter Grid Stopper Resistor Mod. All 3 of those mods I'm going to continue using. Post lots of pics as you build but #1 have fun.
     
  4. milocj

    milocj Friend of Leo's Ad Free Member

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    I don't believe you need to worry about phase when going from the power tubes to the preamp tubes. The preamp tubes are wired as humbucking (technically their 12 volt heaters, but get wired as 6) so from what I've read there isn't a phase issue either from power to pre, or from pre to pre.

    Others can weigh in, but I've even seen arguments that keeping the power tubes in phase doesn't guarantee noise reduction, but in theory it should be the quietest that way. I've never purposely tried to wire out of phase and then rewire to compare, and I haven't checked my vintage amps to see if the power tubes were wired in phase, but none of mine seem excessively noisy, either.
     
  5. Outcaster

    Outcaster Tele-Holic

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    That was my assumption. Thanks.
    We'll see how noisy it is when I fire it up:p
     
  6. Phil_tre

    Phil_tre Tele-Holic

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    I have try it with my 5f11 and 5e3 and I can tell you there is not a single dB of
    difference in noise. At first, phases was inverted and because I read a lot
    in audiophile forum, I correct the phase in preamp. and power tubes. That
    was a pain to do because I wanted to keep the wiring clean but did it anyway
    and again, no difference. Maybe with more complicated circuit but not with a 5e3.

    Fender would probably have use 2 colors wires if it was really that important.

    Ph.
     
  7. SacDAve

    SacDAve Poster Extraordinaire

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    On the negative Feedback switch you might get a high pitch whistle. if I recall it's the switch position with the resistor to the output jack. If that happens you have to swap the OP transformer leads to 6V6's pin 3. So you might want to leave those leads a little long until you test it. On my pic. brown & blue wires. Also on the Power trans. the green/yellow wire (on mine 6.3CT ) should run to pin 8 on one of the 6v6's . Thats something I just learned it help the noise level.
     

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  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    You can also swap the speaker jack wires to stop the positive feedback squeal although it looks 'plain wrong' to run the black to the tip and green to ground.
     
  9. Outcaster

    Outcaster Tele-Holic

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    Phil_tre, thanks for the conformation - I had a feeling the heater wire phase thing is more of a best practice than an absolute necessity.

    SacDAve, thanks - I'm aware of the positive vs. negative feedback and resulting squeal if you get it wrong.

    While we're on that subject, what I don't know is how to tell which 6v6 plate to wire to which side of the OT secondary - is there a way to figure that out or is always just a guess?

    By the way Dave, those are some pretty hefty looking grid resistors you got there - expecting trouble?:p
     
  10. SacDAve

    SacDAve Poster Extraordinaire

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    I went to the V4 closer to the trans less wire. I don't think it matters pins 8 on the 6v6's tied together anyway (jumper)
     
  11. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The power tube plate wires are connected to the output transformer primary wires and there's no way to tell the correct negative feedback phase beforehand. You can also swap the speaker wires instead if there are only two (you can't do this with multiple secondary impedance wires). You could use alligator clips to temporarily connect the transformer wires.
     
  12. Outcaster

    Outcaster Tele-Holic

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    Opps - I meant OT primary:oops:
    On my OT there is only one wire from the secondary as it's grounded to the transformers chassis. So no wire switching there, I'll have to do it at the output tubes.
    That also raised the question of whether or not I need to run a dedicated ground wire for the speaker jacks or if they just ground to the chassis without a separate wire?
     
  13. robrob

    robrob Poster Extraordinaire Ad Free Member

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    As long as the OT and speaker jack are well grounded you'' be fine. I wouldn't run an extra ground wire because it actually creates a ground loop.
     
  14. Outcaster

    Outcaster Tele-Holic

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    Made some progress. Yesterday I got the power switch and fuse wired up and made a modification to the board.
    I put a DPDT Carling switch that provides Off/Stand-by/Play. I did that because I want to use the other switch location (Ground switch) for the NFB switch. Don't really want it hidden between a couple of blisteringly hot tubes...
    Calluses = Good
    Blisters = Bad
    I do intend to play guitar here so I wanted that switch more accessible.

    On the chassis pic you'll see an extra yellow wire which will be the lead from the speaker jack to supply the NFB signal to the switch on the panel. I use a bit of aluminum duct tape to secure it under the board which will have 1/8th inch standoffs leaving a bit of space under it.
     

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  15. Outcaster

    Outcaster Tele-Holic

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    And here's the mods to the board. What I did was clip the V2 bypass cap, bend it up to the top of the board and solder a wire to connect the cap to the NFB switch. I used a bit of shrink tubing to insulate the cap lead and solder joint.
    The idea here is to shorten up these long wire runs as much as possible. My plan (remember, my formal education in electronics ended after I made a potato battery in 3rd grade:eek:) is to eliminate one of the wires in Robrob's design.

    Rather than run a wire from the resistor (normally in parallel with the V2 bypass cap) to the NFB switch and then back to V2 pin 3, I'm leaving that resistor connected to pin 3 as it normally is and running the return from the NFB switch back to the + side of that resistor which will remain connected to pin 3.
    If you look at the bottom of the board where V2's bypass cap normally resides, you'll see second yellow wire soldered to the eyelet at the 1.5K resistor. That wire runs underneath the board (you see it again at the top of the board near that green ground wire) and serves as the return from the center lug of the NFB switch.
    Does that make sense?
    I mean grammatically...
    I wish I had something to diagram it with but basically instead of having the resistor connect to V2 through the switch, I'm having it connect as it normally does. Thus in the middle position, the NFB switch won't be doing anything.
     

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  16. Outcaster

    Outcaster Tele-Holic

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    You'll also see the ground bus added in those pictures above. I used the .064 inch square bus wire that AES sells. It is a royal pain to solder and I'm using a 100/140Watt Weller...
    Sure takes a while to heat that sucker up
     

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    Last edited: Dec 10, 2014
  17. Outcaster

    Outcaster Tele-Holic

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    And now a dose of reality

    If you're reading these threads thinking about how great all these first time TDPRI hep-cat amp builders are, don't be intimidated.

    This is what it REALLY looks like:eek:
     

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  18. Outcaster

    Outcaster Tele-Holic

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    Oh, and one other question - SacDave mentioned the elevated heater center tap in a post above. I didn't do that as I'd only seen it used with an artificial center tap but it does seem that it could be used with a regular center tap.
    Can it? If so, do you just move the heater center tap to one of the power tube pin 8's?
     
  19. Outcaster

    Outcaster Tele-Holic

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    Well, it still looks like spaghetti tonight but I did get the input jacks done. They'd been wired correctly but there wasn't enough slack in the wires to allow me to turn the jack enough to clear the ground bus and still be able to get the Hi inputs into their holes.
    I basically had to take it all apart and re-wire but it's done.

    I also noticed a mistake I'd made at the power switch and fixed that. Not sure what I was thinking but I'd put AC from the fuse to BOTH poles of the power/standby switch.

    I think I'll be able to get the pre-amps sockets wired tomorrow night. Hope so:D
     
  20. MatchlessMan

    MatchlessMan Tele-Holic

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    This is making my soldering hand itch!
     
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