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Harvard 5F10 Build

Discussion in 'Shock Brother's DIY Amps' started by mjcyates, Nov 14, 2018.

  1. Nickfl

    Nickfl Tele-Afflicted

    May 24, 2016
    Florida
  2. mjcyates

    mjcyates Tele-Meister

    Age:
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    May 4, 2010
    louisville ky
    So now that everything appears to be fine, before I button it up, quick question. The chassis I am using has a spot for a standby switch. I currently have a switch mounted but I didn't wire it up. Any cool ideas on how to use an available switch for this amp?
     
  3. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    Negative feedback on/off if the location doesn't add too much noise. No NFB on that thing is instant AC/DC.

    Sent from my XT1585 using Tapatalk
     
    Nickfl likes this.
  4. mjcyates

    mjcyates Tele-Meister

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    Well that sounds interesting. I happen to be a Malcolm Young fan!
     
  5. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
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    Sep 10, 2013
    Georgia
    I ended up with a 100k instead of none to cut some sharp top end, but they may have been speaker related too. Anyway, it turns into a beast.

    100k NFB, 12" Alessandro speaker and P90's.



    Sent from my XT1585 using Tapatalk


    Just realized I had already posted this in the thread, but it's been a while!
     
    robrob likes this.
  6. Lynxtrap

    Lynxtrap Tele-Holic

    634
    Feb 29, 2016
    EU
    Oops, thanks for catching that, I must have been half asleep while writing...
     
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  7. mjcyates

    mjcyates Tele-Meister

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    [​IMG]
     

    Attached Files:

  8. mjcyates

    mjcyates Tele-Meister

    Age:
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    May 4, 2010
    louisville ky
    This is how the amp is currently built with the exceptions of 1) I have not added the 1ohm resistors to ground off pin 8 of the 6V6 sockets, 2) I have not changed the bias resistor to 27k.
     
  9. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
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    Sep 10, 2013
    Georgia
    How are you liking the sound of it so far? Speaker choice?

    Sent from my XT1585 using Tapatalk
     
  10. mjcyates

    mjcyates Tele-Meister

    Age:
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    May 4, 2010
    louisville ky
    I still have a hum to track down but other than that it sounds really good. Currently running a Weber 10A100 10" Alnico. I also have a Warehouse Guitar Speakers G10C which is a great sounding speaker. I also have not decided if I want to make this a head or put it into a combo cabinet.
     
  11. mjcyates

    mjcyates Tele-Meister

    Age:
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    186
    May 4, 2010
    louisville ky
    So currently the tubes I have in this amp are:

    Rectifier: 5Y3 pulled from a Silverface Champ
    Power Tubes: New EH 6V6GT
    Preamp Tubes: New Tung Sol 12AX7, NOS GE 6AT6

    Using the bias pot I can get from 396 B+ to 410 B+.

    Honestly the tone doesn't sound a heck of a lot different from 396 to 410. So is this range acceptable/normal and would you lean to 396, 410 or something in the middle?
     
  12. mjcyates

    mjcyates Tele-Meister

    Age:
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    186
    May 4, 2010
    louisville ky
    So I have some 120 cycle hum that I can't seem to track down or get rid of. The noise is present with the guitar plugged in and not plugged in. The noise is dependent on the volume pot, volume up, noise up, volume down, noise down. The tone pot slightly changes the tone of the noise. I have chopped stick all around with nothing changing the noise. The wire from volume pot to 12ax7 was changed to shielded but didn't really seem to change anything. Any ideas?
     
  13. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    Tried a different tube? If it's always present and volume & tone affect it, there's only so many spots between the jack and volume knob that could have a spotty connection. Bad joints on the heavy gauge heater wire on preamp tubes seems to cause nearly all my mystery hum and noise issues.
     
  14. trippercaster

    trippercaster Tele-Meister

    420
    Aug 13, 2012
    Roanoke, VA
    Hey I just sped through this thread so maybe I missed it, but I am using the 290BX right now and it doesn't have have a center tap for the heaters so you'll need to go the artificial route. If you haven't, that should be the source of most of your hum.
     
  15. mjcyates

    mjcyates Tele-Meister

    Age:
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    186
    May 4, 2010
    louisville ky
    I have tried different tubes. I have a 12au7 on hand that I put in place of the 12ax7 and it is better but that I assume is just because the gain is lower and thus not amplifying the noise as much. The 290BX does have a center tap which I currently have grounded to a ground tab bolted to the chassis.
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    It has a center tap, but not for the heaters - green 6.3v wires. It needs two 100 ohm resistors to ground, usually from the pilot lamp. Check out any Tweed layout - and you'll see. If you don't have those, that is your hum.

    Sent from my XT1585 using Tapatalk
     
  17. mjcyates

    mjcyates Tele-Meister

    Age:
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    May 4, 2010
    louisville ky
    Well the one good thing about this amp build, I am learning a lot. My first amp builds all worked perfectly right out of the gate which was great but didn't offer any learning experiences. I will add the resistors and hopefully that will take care of it. 2 Questions, 1) The red/yellow wire that I thought was the center tap is currently soldered to a tab bolted to the chassis. Should it stay there? 2) Does it matter where I ground the 2 100 ohm resistors? Thanks very much for the feedback!
     
  18. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    The red/yellow is a center tap also and should stay grounded, but the heaters need the 100 ohm resistors if they don't have a center tap - some PT's do, usually green & yellow wire. Go to Mojo's site and check out their 5e3 layout, it shows how and where off the lamp.

    Sent from my XT1585 using Tapatalk
     
  19. mjcyates

    mjcyates Tele-Meister

    Age:
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    186
    May 4, 2010
    louisville ky
    Thanks. I see on Rob's site he puts them on the tube sockets. Is there any benefit to doing it one way over the other? Seems like putting them on the tube sockets would be cleaner.
     
  20. trippercaster

    trippercaster Tele-Meister

    420
    Aug 13, 2012
    Roanoke, VA
    I did it Rob's way on my 5e3 build and struggled with so many things around the tubes (grid stoppers, screen resistors, artificial center taps, plus all the normal connections). I also used bigger wire so that didn't help. For my current 6g3 build I'm putting them on the pilot to reduce the clutter around the tube sockets. I guess it really depends on how good you are with soldering in tight spaces.
     
    jsnwhite619 likes this.
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