1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

RobRob 5E3 Deluxe, 2nd guitar amp build

Discussion in 'Shock Brother's DIY Amps' started by pfarrell, Feb 3, 2021.

  1. pfarrell

    pfarrell TDPRI Member

    Posts:
    55
    Joined:
    Jan 26, 2021
    Location:
    Upstate, NY
    Made 2 Champs—now working on 5E3, RobRob version.

    Stock chassis size—wow, will be tight—just so. Any placement foibles that might lead to noise? I ask, because on the Champ I understand that late in production Fender moved the location of the output jack due to some issues they were having with "sounds". Not sure of the technical, or if that's even true. My Champs are quiet as far as I can tell—which is all very interesting since at the guitar teachers house they actually are quiet and in our house they have some buzz from 4-9 on the dial (All the high-end audio EQ I've made is quiet). I think it's the pot plus AC switch... but am leaving it for now (sounds fantastic to my guitar noob ears, btw).

    For the RobRob 5E3 I'll make some convenient cutout on the back to access the switches. Am I correct in thinking that they shouldn't be switched when the amp is powered up? (Oh, and ignore the non-soldered components on the right of the board, waiting on the bypass cap....and some of the power connections I'll make later of course.)

    PF-RobRob-5E3_02.jpg

    PF-RobRob-5E3_01.jpg PF-RobRob-5E3_03.jpg
     
    DrPepper and mojek like this.
  2. Preacher

    Preacher Friend of Leo's

    Posts:
    4,523
    Joined:
    Apr 17, 2007
    Location:
    Big D
    Cool project.

    When I rewire mine one day I think I will delete the standby switch and put the negative feedback switch in its place. I currently have my negative feedback on the back of the chassis and it is easily reached next to the output jack.

    It looks like yours if going to be pretty tight!
     
  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    4,784
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    What are the switches doing? And you can tag @robrob for fun to get the answer from the man himself.
     
    King Fan likes this.
  4. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,390
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    I may have missed something. What are those switches for, and why are they full-sized? A 5E3 in its chassis is one of the more crowded places I ever want to be. Some extra noise I can picture from yours involves cusswords... :)

    You could fit miniswitches between the novals. But drill the holes before any assembly.

    This is Rob's 3-way NFB/bypass -- its wiring can be very short in this area -- which BTW you can switch on the fly.

    F180802A-8478-4739-A40E-5F148F9181A9.JPG

    BUT check to make sure you can reach 'em through the vents in the back panel. Some neat thinking and wiring got @D'tar a whole control center back there...

    D'tar sockets.jpeg

    If you aren't going to use an extension speaker, that gives you another space.

    Rob does show nicely how to run shielded mic cable down to the ground switch. Clever folks here also put the power switch in the ground slot so the repurposed 'ground' switch is closer to the preamp and further from the 120V. If you have a labeled control panel, you're gonna have some Dymo work, but it's a good switch solution. IIRC Rob also shows how to replace one of the Lo inputs with a pot or switch -- a mini-switch or small round knob on the pot make that easier.

    And are those big power-dropping resistors? I'm not sure where folks mount 'em in a 5E3, but I think there's some room on the 'back wall' between the board and the PT...

    585279C7-AFE4-40BB-88B8-EE74BE8896ED.JPG
     
    DrPepper likes this.
  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,453
    Joined:
    Dec 30, 2019
    Location:
    california
    Welcome to tdpri.

    The 250 ohm bias resistor gets hot. Position the caps so they do not get heated.
     
  6. pfarrell

    pfarrell TDPRI Member

    Posts:
    55
    Joined:
    Jan 26, 2021
    Location:
    Upstate, NY
    Thanks for all the advice/help/words guys. Last first, I'll bend the cap on the bias resistor to the left (or right) when all is in place, there's more space between the 250R and the first pwr cap than looks in the image.

    Left switch is 10% power, right switch is feedback, per @robrob and the 5E3 Deluxe page on his site. Both can be mini?, hmmm, not sure why I didn't realize that—just had them on hand—that would save a ton of room (And makes me glad I posted). Since the cabinet is from scratch I can make as much or as little access from the back as I want—I don't think either of them will get used enough to warrant being up top—but time will tell—and I'm not afraid of modifying later—or building another!!! No crazy noise makers if the wiring for power cut (big resistors) gets longer than optimal lengths? I think with mini switches and AUX output delete there will be a lot of room.

    Great call on deleting the AUX jack. Ha! This won't be the last amp I build (Princeton AA1164 next).
     
    Last edited: Feb 3, 2021
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,453
    Joined:
    Dec 30, 2019
    Location:
    california
    Also push pull pots can be used.;)
     
  8. James Knox

    James Knox Tele-Holic Silver Supporter

    Posts:
    939
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Looks like a fun build!

    If you forego the Standby Switch, you can put the NFB Switch in its place. Or, you can put the 10% Power Switch there.

    Here is a 5E3 I did with the NFB Switch in the Standby hole...


    3AAB262D-AFA5-418D-9E62-576AB55048A0.jpeg


    And here is a Harvard 5F10 with the 10% Power Switch in the Standby hole...

    13FEC203-5627-442E-BA53-D0F2A5667D4E.jpeg 007C0408-8334-44A1-9FD0-8B12A2A2616B.jpeg
     
    Blue Bill, King Fan and robrob like this.
  9. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,390
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    BTW I'm not sure *power* can go through a mini-switch -- I've never looked at their specs. (They're perfectly fine for signal, though.) That nice solution by @James Knox seems ideal, and that’s one switch I might like on the front panel.
     
  10. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    379
    Joined:
    Nov 23, 2020
    Location:
    Finland
    Switch contacts do not wear much when no or very low current runs when they are operated so often smaller switch can be used. Also switcher often are rated for 10 000 and more operations but I don't remember are they full rated current and voltage.
     
  11. pfarrell

    pfarrell TDPRI Member

    Posts:
    55
    Joined:
    Jan 26, 2021
    Location:
    Upstate, NY
    I'm inclined to leave the standby switch on the front panel. Make a cutout for accessing power (output) cut, and feedback swtich from the back. Seems to me that feedback switch could be mini. Dumping the output transfo into the big resistors I'm unsure of the switch requirements there. Certainly the mini switches I have are rated for 3amps, but I'm an electrical noob—and will hunt for some answers, unless someone here can educate me. !! I've read a lot of mod info at @robrob s site... and haven't seen any specifics that state using a large (10amp) rated switch for the power cut, he does get into the the specifics of type of resistor for the mod, like what's been shown in this thread as opposed to the ceramic type.

    EDIT: Actually I just checked Rob's annotated schematic. He notes 1.5A (max?) signal out to speaker—seems that a 3A rated mini switch will be fine... (?)
     
    Last edited: Feb 4, 2021
    robrob likes this.
  12. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    379
    Joined:
    Nov 23, 2020
    Location:
    Finland
    Current = sqr (power / resistance)

    So if 5E3 produce 12W to 8 ohms current is about 1,2A
     
    pfarrell likes this.
  13. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,390
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    You’re doing some good planning and analysis here. But why are you planning a standby switch at all? Read Merlin for a nice discussion of standby folklore and why standby isn’t needed and can hurt not help.
     
    Last edited: Feb 6, 2021
    drew1d and pfarrell like this.
  14. pfarrell

    pfarrell TDPRI Member

    Posts:
    55
    Joined:
    Jan 26, 2021
    Location:
    Upstate, NY
    Good reading. Thanks for this, great timing. I have been wondering how/what the proper usage of that switch is anyway, I'm not approaching it from an educated viewpoint (hence the whole purpose of doing these projects—to learn, so thank you again!)....and will be coaching a 10 yr old in the amps use... I built an Aikido pre-amp (not guitar related, but tubes) which has what is effectively a 3 position power swtich, off, heaters (standby?), full B+ (the use here is more logical than the guitar amp—in my head anyway). It was the recommended pathway from John Broskie, the designer of the amp... I didn't question it at the time, due to the source of the info, so that is the basis of any validation I might have personally. Not debating at all, just curious in this case since the Champ doesn't have such a switch—and I can't yet understand why there might be a difference. And I'm not totally clear on the order of operations, the standby switch doesn't have power until the power switch is on, right, so the heaters get power once power switch is "on", then standby toggles B+.(?) One could just leave standby on all the time, and believe Merlin, to simplify operation. I've also read that one isn't supposed to toggle between standby—like might be thought using the word "standby"—if in a gigging or working environment...Also, @robrob has added some inrush on the standby B+—I do know the value of that from building a lot of power amps.

    If I delete it, NFB or powercut in it's place? Saw some votes for NFB—I guess my instinct is either one would be some lengths of wire across the amp—and I'd probably do whichever one might be less prone to adding noise with longer wires.... Maybe that's not even a concern...but.... Or leave it as is, and save the standby swap/delete for a later project.

    Made a bunch of progress on the build—whoa is it tight around the input jack side (and everywhere). Had to make some changes and lower the board height, rework the ground bus (and bust out some kapton tape to add some extra protection in places). Everything clears—even when a male jack is in place—but it's not roomy!—and I can't orient the Lo jacks for easy tip/switch connections. If I did this again in a stock sized chassis—I'd build a turret board with eyelets, and not turrets—at least on the input side. Also, I had been wondering about the solid vintage style looking fabric-ish covered wire that is available—and its "solid" longevity. I had a longer leg I soldered snap off randomly due to fatigue. It could only have been from me messing about in there and bumping it a bunch of times, not a direct attempt at routing and dressing—I counted about 8-9 bends before it's gone. I'm redoing them in stranded, just too tight in there. For those of you that like coax for signal, is it just about a shielded cable where you don't connect the shield to anything? or?

    I also have a question about the output transformer secondaries. I have black and blue on a Classic Tone 40-18022, and am doing the 10% pwr and NFB mod. I actually wired it up, and then suddenly wondered if black and blue were right. I ran black to ground/switch on the output jack and blue to the power cut switch center (left them long enough to swap if needed). Then I read someplace somewhat randomly that with the NFB mod added the wires should be reversed from "normal". This is prompting a little confusion on the input side as well, with the CT and which leg should go to B+, and which two to the 6V6s.

    I'll post some images later. This is a lot of questions... Thanks for all the help so far!

    Screen Shot 2021-02-06 at 9.37.11 AM.png

    EDIT: Duh, looked at schematic for OT questions. I guess the NFB mod question still stands based on some other reading regarding which wire goes to ground, but I have my wires reversed there currently if "stock".

    EDIT 2!: NFB schematic—I don't see how this affects the OT wiring on the secondaries. Blue is ground for the Classic Tone.

    5E3_NFB_Mod_Schematic.jpg

    EDIT 3!: Just gonna keep updating this in case anyone is doing what I'm doing... found my answer from the man himself here re: OT wiring with NFB mod. See post #7-#11.

    Since I'm also doing the power cut mod—it's a lot easier to swap the P/P tube OT connections—especially once I get heater wires in the way... Will use alligator clips to test at startup.
     
    Last edited: Feb 6, 2021
  15. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,346
    Joined:
    Dec 29, 2012
    Location:
    United States
    It's a 50/50 chance of positive feedback squeal when you startup an amp with NFB. Even when the transformer diagram has phasing dots it doesn't seem to help.

    You can put the NFB switch in the Standby switch hole but I recommend using RG174 or similar thin shielded wire to prevent noise pickup at the noisy end of the amp.
     
    pfarrell and King Fan like this.
  16. pfarrell

    pfarrell TDPRI Member

    Posts:
    55
    Joined:
    Jan 26, 2021
    Location:
    Upstate, NY
    Thanks Rob!!
    At the moment I’m inclined to leave the standby switch alone and keep the feedback switch a bit secret for now especially since I can make the rear access whatever It needs to be.... I can always make it a future update to delete standby..
     
  17. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    745
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    50–50–90 Rule: “Anytime you have a 50–50 chance of getting something right, there’s a 90 percent probability you’ll get it wrong.”
     
  18. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,346
    Joined:
    Dec 29, 2012
    Location:
    United States
    ^ :lol: I'm going to steal that
     
  19. pfarrell

    pfarrell TDPRI Member

    Posts:
    55
    Joined:
    Jan 26, 2021
    Location:
    Upstate, NY
    Some pics... Getting there... haven't connected inputs to board yet—nor finished heater wiring. Was going to use coax, not under board, for preamp tubes to pot wires. It's all very tight....but a great challenge too. Output leads will be soldered last per all the above info in this thread...

    PF-RobRob-5E3_04.jpg
    PF-RobRob-5E3_05.jpg PF-RobRob-5E3_06.jpg PF-RobRob-5E3_07.jpg PF-RobRob-5E3_08.jpg PF-RobRob-5E3_09.jpg
     
  20. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,346
    Joined:
    Dec 29, 2012
    Location:
    United States
    Very nice work.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.