new 5e3 and mods

Discussion in 'Shock Brother's DIY Amps' started by rough eye, Dec 19, 2019.

  1. rough eye

    rough eye TDPRI Member

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    First of all, I'm loving the sounds I get out of this amp. It sounds great, it's quiet and I'm just ecstatic at the sustain and compression. I built the BootHill kit and have a cab from Mojotone, a 12a125a 30 watt speaker, JJ tubes. The build went smoothly and the amp fired up without a problem (except I did screw up by getting a little solder into one of the preamp sockets, which had to be fixed before getting a tube to go in). I spent a lot of time considering how to approach each step before actually executing. I feel my decision to do all the turret board wiring on the top of the board was a good one. One thing i do regret is not locktiting all the mechanical, non-electrical screws and nuts and so forth. Hoping vibrations won't loosen things up.

    I did a couple mods from the robinette website (https://robrobinette.com/5e3_Modifications.htm); specifically, a resistor across the standby switch to eliminate pop, and the "backup" diodes going into the rectifier tube.

    A friend whose electronic knowledge I greatly respect suggested I could also feed all the filaments with DC by adding diodes. Has anyone else done this? I didn't see such a mod on the robinette page but should one be there? If so, anything to watch out for? I wasn't sure if it would simply need 1 diode in front of each line going from the pt to the filaments and light, or if it would need 4 diodes in a bridge. Anyone know a reason I shouldn't consider this?

    Next I'll probably strip the whole amp and finish the cab with some shellac and polyurethane. I've been vacillating on whether to finish it or just leave it raw.
     
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  2. mabinogeon

    mabinogeon TDPRI Member Silver Supporter

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    I've seen maybe two references to adding diodes to the filaments in all the literature I have read on amps and amp building. I don't know of any amps that have that, either (which isn't to say there isn't one - I don't know every amp)

    I don't know of anyone who has tried it, nor if there would be any real benefit to doing so. Can't hurt to try, if you want.

    Won't hurt to put a tiny drop of nail polish on the nuts and bolts after they're assembled - that's what I do.

    I use three coats of shellac typically. First coat is 50/50 clear shellac and denatured alcohol, next two are 50/50 amber shellac and denatured alcohol. I don't think you'd need to poly over that.
     
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  3. D'tar

    D'tar Friend of Leo's

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  4. Wally

    Wally Telefied Ad Free Member

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    Congrats on the build. Re: DC heater filament voltage. Imho, it is not necessary in this amp. High gain amps benefit from running DC voltage to the heaters in the preamp section to keep noise down. You do not have a high gain amp, there; and you seem to be happy with the noise level.
     
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  5. muchxs

    muchxs Doctor of Teleocity

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    If it don't hum, don't fix it.

    I test all my builds by turning everything all the way up, no instrument plugged in. I usually hear no hum, no hiss. It's hard to tell the amp is on if I have a goofy pilot light bulb. You'll have that with imported "47" bulbs.
     
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  6. rough eye

    rough eye TDPRI Member

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    there was a little problem with noise at first but it turned out the input jack tabs had to be bent a little. the jack wasn't grounding out when there wasn't a cable plugged into it. makes me wonder how many times guys beat their heads against the wall not realizing it was such a simple fix.
     
  7. printer2

    printer2 Poster Extraordinaire

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    Gridstopper in the PI.
     
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  8. rough eye

    rough eye TDPRI Member

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    i read an article on blocking distortion and it listed as the first solution to reduce the coupling capacitor values. Per Dave at BootHill i have, instead of .1µf for the caps between the first and second preamp stage, a .01 and .022 cap (going to the normal and bright pots, respectively). Would that make adding a resistor into the phase inverter redundant?

    I've tried my pedalboard into the amp at about the level i intend to push the front of the amp but not at high volumes yet. I haven't encountered any problems, but hoping I can still say the same after I've tried this amp out with a band.
     
  9. Nickfl

    Nickfl Tele-Afflicted

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    No, but it's a good mod if you don't like the boomyness / flabbiness / fartiness whatever you want to call it that's inherent in the 5e3. But it will change the overall sound a lot more than a grid stopper on the phase inverter, and I'd still throw grid stopper on there even if I was doing the smaller coupling caps. IMO, the phase inverter grid stopper on a cathodyne PI amp is a no-brainer standard mod like back up diodes on a rectifier tube, it helps prevent blocking distortion and there's really no downside to it.
     
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  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    If it's a new Mojotone cab with tweed already on it, I would advise against stripping and finishing. I assume you mean "no tweed/tolex, just finished wood" by that statement?

    A) you don't know what kind of knots/filler is under that tweed already
    B) whatever glue they used is going to be a BEAR to remove completely enough to look decent as a finished wood cab. And you may damage it in the process.

    I've stripped and restored several old cabinets. It's not fun, and there's no way I would do it unless it's getting covered again. If you really want a finished wood cab, and that's a new cab in good condition, I'd sell the Mojo and get one from the Raw Cabs guy on Ebay or something along those lines. Break even or maybe come out ahead, and save a whole lot of work in the process. Stripping and prepping the tweed cab will be more work than the finishing.
     
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  11. Doctor49

    Doctor49 TDPRI Member

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    +1
     
  12. muchxs

    muchxs Doctor of Teleocity

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    Don't do that.

    Like Jason White says, it will be an epic pain. You get to choose your own location for your epic pain.
     
  13. rough eye

    rough eye TDPRI Member

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    sorry, i guess i shouldn't have used the word "strip." I meant remove the chassis, baffle and all hardware, so i could apply something to the tweed to seal and protect it. i'm not totally decided on whether i should do that or just leave it as is, and almost 100% decided shellac would be the way to go if i do.
     
  14. muchxs

    muchxs Doctor of Teleocity

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    First coat is usually clear lacquer. That prevents blotchiness in subsequent coats of shellac.

    You want to reduce both your lacquer and your shellac. Use lacquer thinner for your lacquer and alcohol to reduce your shellac. Use approximately 1 part alky to one part shellac.

    This is where it gets tricky. I use Zinnser "Bull's Eye" shellac. It's lighter when it's fresh and darker as it ages. Youi want to cut it with alcohol to get your desired amber in two coats. One coat tends to be uneven.

    You don't want a thick shiny buildup.

    Last coat should be clear lacquer.

    I wouldn't to my first attempt on a $250 Mojotone cabinet. Mojotone charges $40 for lacquer.


    Some guys use Minwax honey pine. It's mot lacquer or shellac.
     
  15. King Fan

    King Fan Friend of Leo's

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    This is kind of a funny way to back into a tweed-finishing discussion, :) but I notice you say shellac and poly. That would work, of course -- "shellac sticks to everything and everything sticks to shellac."

    No harm, I guess. Some people find poly gives a 'plasticky' sheen, shellac looks more vintage. If I were gigging it, transporting it with the drum kit, and expected folks to put beers on it, I'd *definitely* put poly clear on top of shellac. For home use or gentle use playing out, all-shellac would be easier and might look better. As muchxs says, clear first, then at least 50:50 amber cut with denatured alcohol x 2+ coats, then a clear shellac overcoat. The biggest problems we see are blotchy and overly orange -- again, read muchxs.

    What are your goals? Simple? Looks good? Durable?
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I had an old Bassman clone cab through here recently, and I think it must have been finished with poly. It had a very "encased in plastic" look. Assuming I'm correct that it was poly, I would not particularly recommend it over shellac. Though, a couple cans of shellac, denatured alcohol, brush or two, sandpaper....you'll easily have $40-50 tied up in finishing a Tweed cabinet.

    Sent from my moto g(6) using Tapatalk
     
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  17. Bergy

    Bergy Tele-Holic

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    Congrats on the amp. I've got a 5e3 kit coming in the mail on Monday and this is a really helpful conversation to read as I'm studying up.
     
  18. Paul G.

    Paul G. Friend of Leo's

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    Authentic would be shellac, cut with alcohol.

    I use my amps, so less authentic is fine. 1 Coat of Minwax Poly clear. 2 Coats of Minwax Poly Honey Pine. Looks fine, wears well, you're done and dry in 2 days.
     
  19. rough eye

    rough eye TDPRI Member

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    so i followed mabinogeon's suggestions and put a bit of nail polish on all nuts holding stuff down. funny, i was looking at photos of the inside of an old, vintage deluxe and saw the same sort of thing was done. i also followed his suggestion with the shellac; i put one coat of clear, followed by 2 amber. i was going to do a 4th, clear coat at the end but since it's COLD outside and i was in an enclosed room (to keep cats from climbing on freshly shellacked cabinet), i stopped after the 3rd coat. Finish is a little uneven, but my main goal was to protect the tweed from fraying and so on. I'm sure it will never look uglier than some of the guitars i play, and my strat and tele cases have patches of bare wood showing where the telex has worn off. I also realize I can rub down the darker areas with alcohol at some future date to smooth it out a little but I'm not too concerned.

    I also added that grid stopping resistor on the phase inverter, although i don't know what grid stopping or blocking distortion is. Listening to the amp I can't tell if there's a difference or not; initially I felt it might distort a bit earlier but that might have been an illusion - or maybe it's the shellac :)

    One thing i'm wondering about is how hot the chassis gets after being on a few hours. Maybe it's just that I'm not used to having a tube rectifier. Anyway, I've built and wired a few guitars but this is the first time I ever built an amp from the ground up. It's been a really rewarding experience and this forum has been a huge help, so thank you all!
     
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