First Build - 5e3 build... got some questions

Discussion in 'Shock Brother's DIY Amps' started by buffalohunt, Nov 3, 2019.

  1. buffalohunt

    buffalohunt TDPRI Member

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    Hi everybody!

    I've been active over on the Tele Home Depot page for a few years, but figured I would try my luck at an amp build.

    Long story short, I ended up with a Mojotone 5E3 Tweed Deluxe kit. I actually pieced together my own kit from them because I wanted a multi-tap output transformer, a different sized chassis (I am making it into a head unit, not a combo) and I already had some of the tubes.

    I've mostly finished wiring up the amp and only have the speaker outputs and "ground" switch left to do.
    I've intentionally left them for last.

    I couldn't decide if I wanted to leave the switch as a more-or-less useless ground switch or modify it to use as either a standby switch, or just a simple mute switch. I've done some reading on both, but admittedly I am not super knowledgable on amp electronic circuitry. I have a basic understanding of electronics, but that's it. I'm leaning more towards making it a mute switch because it seems simpler. I am just a bit worried about noise that could interfere on that end of the chassis (my chassis has the same general layout as the original 5e3, just with some more room around components). I've read about using shielded coax cable to keep the interference down. I have a bunch of this shielded guitar wire (the kind that Gibson uses in their guitars. Would this work for wiring a Mute switch?[​IMG]

    Second question...

    My output transformer has leads for 4, 8 and 16 ohm options. I am hoping to be able to plug in either an 8ohm cabinet, a 16ohm cabinet and possibly someway to have 2 cabinets if I wanted. Is this possible? Can I wire up two 8ohm parallel plugs, similar to how all Fender amps comes standard, and then have two extra plugs for 4ohm and 16ohm?
     
  2. Preacher

    Preacher Friend of Leo's

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    OK for your first question, I would say neither. For the newer 5E3s the standby switch really doesn't do much per se, and I think a mute switch is something that I would use on my pedal board or if I was playing direct into the amp I would just turn down the volume.

    Look at Rob's 5E3 mods.
    https://robrobinette.com/5e3_Modifications.htm
    The NFB switch would be my choice to put in that space on the face plate. I t really does give you some different tones and since I use my 5E3 for other guitars other than a tele (shocked face) it really helps with humbucker guitars. I have my switch at the rear of the chassis and I wish I had some forethought that I could have put it on the top.

    I would use the shielded cable on the long signal chain runs and if you decide to use the mute switch. Make sure you only ground one end of the shielding or you will make a ground loop. I have seen amps completed both ways, with and without shielded cable.

    On your second questions, check out Robs page again (it is kind of the holy word on amp building). You could have a switch mounted on the back that would allow you to set impedance for the output, or you could do as I did on my Valve JR build where I wired in three different output jacks, one for 4, 8 and 16 ohm cabinets.
     
  3. D'tar

    D'tar Friend of Leo's

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    IMO....

    That type of wire has no business inside a tube amp! conductor on the outside not a good idea. get yourself some rg174.




    upload_2019-11-4_10-58-6.jpeg
     
  4. King Fan

    King Fan Friend of Leo's

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    I agree with @Preacher . Re ground switch, read Merlin Blencowe on standby (spoiler alert: useless and possibly harmful) and then decide if you really need a mute switch. And if you really do, what @D'tar said, I'd use heavier shielded cable like RG174 -- IIRC guitar cable is not dealing with 120VAC very often. :D

    And yes, Rob's 3-way NFB is a nice mod. But for the sake of ease, I put it on a mini-switch like Rob does right at the edge of the 'vent' in the rear panel near the speaker jacks -- clean short easy wire runs. It isn't much of a switch-on-the-fly option, and my fingers find the switch really easily. If you really need it on the control panel, Rob also points out you can steal a lo input jack hole. I ended up leaving my ground switch as an unconnected switch -- someday I may run Rob's MV circuit over there using his microphone cable. I figure MV really does need to be on the control panel.

    Re mods, you can plan for them now (drill holes, extra eyelets) but all smart advice is not to wire 'em in until you have the stock amp working, and learn how the stock amp sounds. Also, of course, make them defeatable so you can get back to the stock settings.

    Finally, a multi-tap OT is great, but read Rob's advice if you add the NFB -- you only need to set up NFB for one impedance. But I agree with Rob and Preacher -- an impedance selector switch is more elegant, simpler, and (best of all) way reduces the odds you might leave your amp with no speaker plugged in, or worse, no speaker plugged in and an OT connection through a non-shorting output jack. Pfffft... :)
     
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  5. Wally

    Wally Telefied Ad Free Member

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    Buffalo hunt, regarding the multi tap OT and possibilities, there are a number of ways to go about it. You could install a switch to choose the impedance tap to send to the jacks with multiple jacks to accommodate various paralleled speaker loads as Marshall did. That is, with the 16 ohm tap, you are limited to running one 16 ohm load. In the 8 ohm tap position, you could run two 16 ohm loads, which is 8 ohms in parallel, or a single 8 ohm load. With the 4 ohm tap, you could run a single 4 ohm load, two 8 ohm loads, or 4 x 16 ohm loads.
    As for mixing loads, I don’t. There are some rare OT’s that have totally separate secondaries for the different load impedance, but most of these multi tap OT’s use taps on a single winding to achieve the multi tap result. I have no idea what the result of plugging matched loads into the proper jack in such OTs. When mixing loads on a single impedance, the lower impedance load will be worked harder than the higher impedance load due to that difference in impedance. I believe in using the same loads when using separate cabs, and I believe in matching that total load to the OT tap. Ommv.....
     
  6. Preacher

    Preacher Friend of Leo's

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    Great catch @D'tar , no exposed shielded wiring should be used in the amp. Too many options for a hot line to touch!
     
  7. jman72

    jman72 Tele-Afflicted

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    Maybe I'm in the minority, but I LOVE having the standby switch on my 5e3. I use it every time I play, mostly as a mute switch when I need it or between sets. My buddy has been playing a different amp for the past couple of years WITHOUT a standby switch and he hates not having one. He just built his own 5e3 and adding a standby switch was a no brainier.
     
  8. Paul G.

    Paul G. Friend of Leo's

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    Leaving an amp on standby for 20 minutes at a time is not the best idea, I'd rather leave it on. As for muting the amp, I just pull the plug halfway out of the jack, and done -- no extra circuitry.

    I used the hole to add a pre-PI master volume. On this particular circuit it works beautifully.


    mm 5e3.jpg
     
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  9. schmee

    schmee Poster Extraordinaire

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    I like using a switch for the OT taps. Whatever you do, standard inclination is to attach the NFB wire to the original impedance tap (8 ohm in your case)
    I also agree with not using that uncovered shielded wire in an amp. Although you could put a covering on it if you want.
     
  10. jman72

    jman72 Tele-Afflicted

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    I've heard that it is not a good thing to leave the standby switch on, but have also heard that it's fine. What damage could it do? I've not had any trouble yet, but don't want to screw it up.
     
  11. King Fan

    King Fan Friend of Leo's

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    You probably won't hurt your amp using standby as a mute switch for short periods. You're actually in the majority that 'want' a standby switch; you're also in the smart half of that majority who like it cuz it can be a mute switch.

    As for the potential harm and the several wrong-headed other reasons people 'want' standby, it's all in the Valve Wizard piece linked in my earlier post.
     
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  12. Paul G.

    Paul G. Friend of Leo's

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    With no load the B+ voltage can fluctuate. In addition there is a possibility of cathode poisoning.

    Listen, there are two sides to this, and some claim it's perfectly fine. If there's controversy, I prefer to err on the safe side.
     
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  13. RottenTheCat

    RottenTheCat Tele-Holic

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    Let me rock the boat, and upset everyone's day.

    I leave the ground switch wired as it was first designed, with two changes.

    First - run the black wire through the fuse first, then on/off switch, then ground switch and transformer. In normal, sane, and correct modern wiring, that will give you the best protection.

    Second - I do not wire the capacitor (on the ground switch "common" contact), directly to ground, but run it through a fuse to ground. Make the fuse .125 amp, normal blow, or .1 amp normal blow (if you can find one). Should the SHTF, the fuse will open, you're good. Why wire it at all? Because not all wiring is normal, sane and correct. Too many stages are isolated, or ungrounded, or the sound guy ran an extension cord with the ground missing, or its old and only wired with two wires, or in disrepair, or whatever. The ground switch will let you take out the hum in that case, and the fuse will keep you safe, should you want to weld your lip to the microphone who's ground is opposite.

    The hum has almost zero current, so the smallest fuse you can find is just fine in there as a "protective" device.
     
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  14. buffalohunt

    buffalohunt TDPRI Member

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    It looks like I could match that by just putting shrink wrap over the guitar wiring
     
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  15. D'tar

    D'tar Friend of Leo's

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    sure that would be fine, use what you have. If you have to purchase anything rg174 cost less than shrink tubing per foot. Penny here, penny there. My comment was regarding safety having the outer conductor.
     
  16. King Fan

    King Fan Friend of Leo's

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    Giving your solution a shout-out. I hadn't thought of moving the power switch over to the ground hole and slotting the MV where it had been. Two big advantages from that one simple move -- less AC noise at the MV, and (subtle but key) room for a chicken-head knob to turn. Nice.
     
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  17. Paul G.

    Paul G. Friend of Leo's

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    Yup, you're not really close to the AC if you route the wires correctly. I've got a shielded cable coming from pin 7 of V2 -- mostly because it's a long run, the other connections are just wire (twisted 'em because I'm OCD). No hum at all compared to where it was before. And having a chicken head knob instead of a little round one is nice.
     
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