Starting 5F1 build soon — questions

Discussion in 'Shock Brother's DIY Amps' started by rycolos, Oct 18, 2021.

  1. rycolos

    rycolos TDPRI Member

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    Hi everyone! Very long time lurker on this forum, but for some reason I haven't joined.

    I'll be starting my first amp build soon, a 5f1. Parts + chassis are coming from Tube Audio Supply, transformers and speaker from Weber, cabinet from eBay, and I purchased some nicer filter caps from AES. I'll be using the latest RR layout.

    I have a few initial questions, primarily safety related but others as well. I have been building pedals and doing a variety of other electronics projects (RasPi, Arduino, some home elec) for over 10 years. This, however, will be my first tube amp and I'm admittedly a bit apprehensive about high voltage. I've read RRs safety guide and I feel pretty confident in how to stay safe, but a couple questions:

    1. Bleeder Resistor — I've read that adding a bleeder resistor on the filter caps will decrease the time required to rid those caps of high voltage (with that caveat that you still must always verify with the multimeter). I believe I just need to add a 220kish 2W resistor from the first filter cap to ground. Is wiring that resistor as simple as placing it in parallel to C3 in Rob's layout? Can it share the same turrets?
    2. Basic safety — Once the filter caps are drained and the amp unplugged, are there any remaining risks inside of the amp? My basic electronics knowledge says no, but no harm (literally) in verifying!
    3. Reducing hum — In a couple of D-lab's videos, he's mentioned that moving the speaker jack to between the power and rectifier tubes can reduce hum. Would it be prudent to just do this off the bat rather than waiting to see if any hum is present? I'm planning to add an NFB removal switch and I could repurpose the original hole for that. In addition, would it be wise to use shielded wire for particular connections in the amp, like input and output jacks?
    4. Bias — Also from D-lab's videos, he mention that 470R often isn't high enough to bias a 5f1 connected to the modern electrical grid. Rather than wiring this in from the start, would it be better to omit it and start with alligator clips and potential values? I've never worked with turretboard before, so maybe it's easy enough to replace components that it's better to start with something present. I hate hate hate desoldering from PCBs and stripboard.
    That's it for now...as if that wasn't a lot!
     
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  2. rycolos

    rycolos TDPRI Member

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    2nd post made by mistake
     
  3. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    Welcome to the club!

    1 - Sounds right to me
    2 - Nope, but always verify with a meter that there's nothing stored in the caps before sticking your hands in there
    3 - I wouldn't
    4 - There's tens of thousands of Champs and Champ-ish things out there running just fine with those values. You certainly could try clip leads though if you need to mess with the values as that won't hurt anything. You'll likely (and should) get over 100% dissipation in a Champ, which is fine as long as the tube you're using doesn't redplate.
     
  4. VintageSG

    VintageSG Friend of Leo's Silver Supporter

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    1. Bleeder resistor = good idea. Verifying with a multimeter = a good idea.
    2. Filters drained, amp unplugged = safe, in the main, but verify anyway.
    3. Hum. Careful wire routing and twisting ( where needed ) and laying heaters along the crease of the chassis -or- elevating them will go a long way to reducing hum. If you can't hear it when playing, don't bust a blood vessel trying to eliminate it. Seriously. 10 minutes of lead dress is worth 40 hours of hum-shooting.
    4. Croc clips and playing with the values is one way to go. Turrets are easy to work with compared to PCB and Vero. The 470R value may well be correct for the majority of valves you buy. If the amp is between 95%~115% at idle, it'll be fine. You -may- wish to add another value on a switch though to suit ( say ) an EL84 or 6p1p-EV via socket adaptors.

    Enjoy your build. Don't zap yourself, and photographs of the finished article are expected. Print out copies of the schematic. When each section is done -and verified-, use a highlighter to mark that it is complete and measures as expected. Make a voltage chart.
     
  5. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    What they said. For the bias resistor, if you worry you’ll need a higher value, solder it into the top well of the turret, which is (a bit) easier to unsolder than the wrapped sides. Don’t go too high on the resistance in any case. More generally, Mr. D-lab is generally fine, but he has areas where he's idiosyncratic, and a couple where he gets crazy. Rob's pages are a good guide.

    Also welcome, and keep asking questions as you plan and build.
     
  6. Junior Little

    Junior Little Tele-Meister

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  7. andrewRneumann

    andrewRneumann Tele-Afflicted

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    +1

    For any component you might be experimenting with, do this ^^^^. Leave the leads long so you can grab them easier with pliers and use the component again on your next project. Easy to clean up the center of a turret with a solder sucker too--and oh so satisfying. Welcome and good luck!
     
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  8. sds1

    sds1 Tele-Afflicted

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    With the bleeder installed this tool will sit in the drawer. A good thing imo!
     
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  9. Junior Little

    Junior Little Tele-Meister

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    For this particular build, sure. Fair enough. But who knows what the future holds...
     
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  10. pfarrell

    pfarrell TDPRI Member Gold Supporter

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    Consider NOT using the combo power and volume switch/pot. Deleting this was the only way I was able to make two Champs I built as starter projects quiet. Having ZERO real life experience with any guitar amp in person—I wasn't sure what to expect in terms of base level "noise". There was more than I was comfortable with (coming from the world of hifi DIY amps where quiet is king)...So I moved the fuse to the bottom of the chassis and put a dedicated power switch in its place, then a normal vol pot. No regrets. Still a little noise—but I think that's likely normal—shielded wire where it matters most.... Now, my @robrob 5E3 build—That thing is freakish quiet. (and... welcome to the forum!)
     
  11. Telenut62

    Telenut62 Poster Extraordinaire

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    Welcome, I hope you're going to put 25uf capacitor on the cathode resistor?......you won't regret it.

    https://robrobinette.com/How_Amps_Work.htm

    Or...if you want to up the ante a bit....try a GA5 circuit only 3 resistors difference but what a difference, like a mini Marshall.
     
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  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Welcome to TDPRI.

    A few tips:
    Many of the resistors get hot. Caps are better off not getting hot. Keep a space between them. Remember heat rises. Do not put a cap directly under a hot resistor if you can help it.

    (Rob has not corrected his 5F1 layout yet.) Swap the position of C6 and R8. This will put C5 and C6 next to each other. The hot bias resistor will no longer be between them.

    The bleeder resistor can attach to the terminals of C3, but keep a space between the resistor and cap.

    Check the chassis for sharp edges when it arrives. A file or sandpaper can dull the sharp edge so you don't cut your hands in that small chassis. Maybe even put some painters tape on the chassis to protect it and you.

    There are a lot of comments about added noise because of the combined volume pot/power switch, if you can, use a separate power switch.

    Use a 1/4 jack for the speaker. Ditch the RCA speaker jack.

    Drill a separate hole in the chassis for the power cord ground wire connection. You might consider drilling other holes for connecting a ground bus or two. (Separate bolts are less likely to loosen.)
     
  13. rycolos

    rycolos TDPRI Member

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    Thanks for all the feedback, everyone.

    Building a current limiter this weekend and just purchased a capacitor discharge tool from Weber (was a bit nicer than DIY).

    Yeah, I've been reading a bit about this. I think I'm going to go stock for now and see how things go.

    Yup! Is it best to put one on v1a and v1b or just v1a? What's more "stock," recognizing that "stock" can be a fleeting concept.
     
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  14. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Just like this (but noting LLC's good idea of swapping the output bias cap and resistor positions for heat management, and trying to use the good idea of a new hole for the fuse in the bottom so you can put a switch in the fuse hole).

    Rob_5F1_Layout.jpg
     
    Last edited: Oct 21, 2021
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  15. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

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    I don't know what your experience level is, but learn to solder before your parts start showing up. Bad soldering probably sinks more projects than any other cause.
     
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  16. rycolos

    rycolos TDPRI Member

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    Re: power switch, I've purchased an internal fuse holder and will put a carling spst in the place of the original fuse holder.
     
  17. rycolos

    rycolos TDPRI Member

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    Some more questions as I've read through previous build threads, primarily grounding related:

    1. Is there any consensus on best grounding method? I'm seeing competing "best" methods, primarily "ground AC, power, and preamp to chassis at separate points" vs "ground them all at one point." I'm inclined to follow the Ron layout because it's simple and all there to work from, but figure it's worth inquiring.
    2. Is there a benefit to isolating input jacks, pot, and 1/4 speaker jack?
    3. If input/pot/output aren't isolated, do they need to be directly grounded via wire or is the ground via their chassis mount good enough?
     
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  18. 2L man

    2L man Tele-Holic

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    I think it is good NOT to use chassis for any return current because problematic two prong instrument cable neutral connects there. When all current return to power supply thru ground wire(s) and ground is connected to Chassis only at amp input, then technically it is shorted to Earth best.

    If current flow thru chassis it can "wiggle" guitar in the end because there is resistance in Mains Earth wire and some of this noise can come back to amplifier input.

    There is no consensus and there are amp builders who think extra noise and hum can be wanted effect for vintage sound?
     
  19. Gris

    Gris Tele-Meister

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    The version with a choke is the quiet one.
     
  20. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Can of worms opened…

    1. Rob's plan is perfectly quiet, but 2L man and other purists here are right; a single ground may *theoretically* be better. And a single ground is simple enough on a 5F1, but should be done right. Do you have a drawing or build pic you can show us? I’d agree with your plan to do Rob's way, as it’s clear, easy, and has been used on hundreds or thousands of similar amps.
    2. Isolated jacks are theoretically better, too, but you need a step drill and shoulder washers. I do it, but I bet 95% of good builds here don’t. Pots? Not sure I see those being isolated. OTOH… best practice is a) don’t ground the lugs or bus to the pot case; b) do use a star washer underneath… if nothing else, prevents rotation.
    3. If not isolated, do put a star washer under jacks to maintain good ground. In that case, the ground to the jack shell or pot case is fine, but as noted, ground the pot *lugs* to your ground bus / wire.

    Simple foolproof way, build it to Rob's layout, optionally with my notes above. If you’re a more ambitious/confident/idealistic builder, show us the plan you want to follow instead. There are several right ways, but many wrong ways… :)
     
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