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5F11 Tweed Vibrolux build

Discussion in 'Shock Brother's DIY Amps' started by DJLockjaw, Jan 3, 2021.

  1. DJLockjaw

    DJLockjaw TDPRI Member

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    Just starting my second amp build, and figured I'd put a thread up to document and ask the occasional bit of advice. The 5F11 doesn't seem to be very popular either, so maybe someone else will learn from my (inevitable) mistakes. My previous build was a Mojotone Studio One Marshall-flavored high gain amp, which is an awesome piece of kit. The clips I've heard of the 5F11 might be my favorite clean sounds that I've ever heard, and the tremolo is a neat little feature too. I'm hoping this build goes nice and smooth since the 5F11 is a simpler amp than the Studio One. It should also give me a little more experience working in a very tight enclosure.

    A little about the build so far:

    I'm using Mojotone's chassis and small parts kit to simplify sourcing parts. I've got everything mounted into the chassis that I've got on hand now. I'm not using Mojotone transformers - the two I got with the Studio One kit weren't great. The heater voltage was only 5.9v unloaded on the PT, and the first output transformer I got was blown from the start.

    The transformers I'm looking at are the Hammond 290HAX PT (https://www.hammfg.com/files/parts/pdf/290HAX.pdf) and the Hammond 1750E OT (https://www.hammfg.com/electronics/transformers/classic/1750). My hope is that the slightly lower voltage of this PT vs Mojotone's (275v vs 350v) will help tame it a bit and keep it a little quieter. I've read that the B+ on Mojotone's kit is a little higher than original 5F11 examples, too, so I might get pretty close to the original voltages. I'll have to drill the chassis for the OT because it's a little smaller than the Mojotone one. If anyone has a better recommendation for an OT, feel free to let me know. I haven't ordered yet, since I've also got a pile of pedals that I need parts for and figured I'd put it in all at once. I'll be building the cab out of a bee box that's on order, with probably a 10" speaker but I haven't selected that yet. I really want to do a TV front, coffee bean cutout kind of thing. My hope is the end result will look like classic furniture instead of an amp.

    Just so you guys can see a picture of what I've done so far, which admittedly isn't much:

    Chassis.jpg
     
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  2. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Here was one I built a few years ago, same OT, same specs as the HAX I think PT using a 275V tap, C-Rex speaker. We've recently determined in a couple of threads that the Hammond 1750E is more of a Princeton OT clone instead of a 5E3 clone, but I've used it for several amps and I've been happy with it.

    Here's the amp demo.

     
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  3. Muzzy

    Muzzy TDPRI Member

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    I've got a 1750E OT if anyone's interested.
     
  4. Mark the Moose

    Mark the Moose Tele-Afflicted

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    I built a mojotone 5f11 a couple of years ago and it’s excellent.
     
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  5. dankilling

    dankilling Tele-Afflicted Silver Supporter

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    Do the adjustable bias mod. It’s worth it so you can also tune the tremolo
     
  6. DJLockjaw

    DJLockjaw TDPRI Member

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    Jason, definitely loving it. I can't play that good either, but that sure does sound sweet. Do you recall if the third red wire to ground from the PT is the red/yellow 0v tap? I think that might be a mistake coding it as red on the Mojotone website, but I'm rubbish at reading schematics so can't be positive.

    https://www.mojotone.com/Amp Kit Sc...ime=184481&gc=clear&promocodeaction=overwrite

    Definitely doing the adjustable bias mod - all the threads I've come across are about how the tremolo isn't slow enough without it. Part of the reason I'm looking at the 290HAX vs the 290CAX is the bias tap.
     
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  7. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Yeah, the Hammond CT is usually red & yellow, I think that goes for most PT's in general. I've used the CAX and the 290AX - I would go with the 290AX of those two, though neither have a bias tap. It really isn't a big deal to make do without one - change 1 or 2 resistor values and get the voltage from the rectifier pin. But, it's a little lighter weight, still a 100mA rating with 2 voltage options, and if you are stateside, you don't need the extra primary options for the CAX. It just ends up with a LOT of wires in there.

    Definitely build it with adjustable bias. If I remember correctly, the bias helps with the depth of the tremolo more than speed, but I may be wrong. You can play with the coupling capacitors in the trem circuit to slow it down if needed.
     
  8. brucerbc

    brucerbc TDPRI Member

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    Great to see a 5F11 build thread!

    I've got one underway too, also in Mojotone chassis ... after they replaced a lost shipment!

    Waiting now for a few parts to finish.

    Transformers I selected were:

    Hammond 1760H - Output Transformer - 4/8/16 OHM

    Hammond 290CAX - Power Transformer

    Hope they prove right!

    I'll be watching this thread for tips for sure!

    Thanks for sharing.
     
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  9. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Heh, Jason, you're just being modest -- you're right, of course. DJlockjaw, you're in luck -- Jason totally knows the 5F11, including PT and OT choices, B+ voltages, and everything else. So pick his brains. Also, adjustable bias is nice for lots of reasons -- like getting the tone sounding 'best' to your ears and keeping your output tubes happy -- but re trem, as bias becomes too hot, tremolo gets weaker.
     
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  10. DJLockjaw

    DJLockjaw TDPRI Member

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    Bruce, that's crazy about the lost package - I also had an adventure getting mine. I got a tweed bassman chassis and a whole bunch of knobs in my box. Mojotone put together the kit for me and sent it out as a rush.
     
  11. jsnwhite619

    jsnwhite619 Friend of Leo's

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    As I said above, some recent threads and digging have uncovered that the 1750E is more of a Princeton Reverb OT clone than the Tweed years OT, the latter being bigger. The 1750-1760H is the 125A1A Deluxe Reverb clone OT, much more headroom and clean output. Since you mention wanting to keep things on the low side of volume output, I'd suggest the 1750E - the one you mention. I've used the other OT on a Harvard build, and it was incredible clean tone, but it was noticeably louder and bigger bass -- like rattle the pictures on the wall bass with the right speaker.
     
  12. brucerbc

    brucerbc TDPRI Member

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    Putting together an order now to complete my 5F11 build with the 1750E as suggested. :(, but grateful for the learning.

    I clearly didn't think hard enough when reading the Hammond website: it said the 1750H was a replacement OT for the "Vibrolux", but in retrospect I understand they meant the blackface amp, not the tweed.

    If COVID has taught me one thing, it's to keep on keeping on!
     
  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    If you aren't gigging with it and needing full horsepower out of it, I've built more than a dozen amps with that OT. Never wanted more volume or headroom out of any of them. A tip for these 5f11 amps -- the trem works on the low frequencies. A bass heavy speaker can help of you want the really thick tremolo. The trem cuts out at a certain frequency, it is a low frequency deal, so you don't want a speaker that shelves low end too much.
     
  14. Emiel

    Emiel Tele-Meister

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    In case you haven't decided on a 10" speaker yet, I can definitely recommend the Jensen P10R-F. I have one in a 5F10 Harvard (housed in the bigger Deluxe enclosure just like the Vibrolux). Transformers are the Hammond 290CAX and 1750E. I think you'll love the Vibrolux. It has a great clean tone with a bit more headroom than the Deluxe. I like it better turned up too as the low end stays a bit firmer. Good luck with the build!
     
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  15. Kevin Wolfe

    Kevin Wolfe Tele-Holic

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    I love mine! I did the bias pot mod and a switch on the NFB. Just yesterday, I went back into it to clean up a ground loop issue at the inputs and while I was there, I dropped the input grid stoppers to 27k and added a 120pF cap from V1 pin 2 to ground as suggested in a Merlin article. I’ll be posting about that later with some pictures.
    By the way, the 5f11 is a sweet acoustic amp with a touch of tremolo.
     
  16. DJLockjaw

    DJLockjaw TDPRI Member

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    Well, I've made a little bit of progress. The board is finished (mostly). Still waiting on a 33k resistor from Mouser for the bias mod, and the bias pot. I'll be using a 25k pot instead of the 10k Mojotone recommends - that should give me a little more travel. The original circuit is built with a 56k resistor, and the Mojotone recommended pot and 33k resistor in series won't give as much resistance full on as the original circuit. It'll be a while before I can do anything else - next steps are to mount the transformers, and the PT is on backorder.

    I also found a couple of errors on the layout diagram - there's a 470R resistor marked as 4.7k, and the center tap from the PT HV secondary goes to ground but is colored wrong on the diagram.

    If anyone wants to take a once-over on the board and let me know if I've put a cap in backwards or if there are any obvious wiring mistakes, I'd be grateful. Finished board.jpg
     
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  17. Kevin Wolfe

    Kevin Wolfe Tele-Holic

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    Looks pretty good. Some folks are gonna tell you to add some separation between the V1 cathode resistor and its bypass cap due to the heat generated by the resistance.
    Having said that, the originals I’ve been in, and I’m talking about old ones, those caps and resistors were mounted against each other with no ill effect for over 50 yrs. Go figure.
    If I were to change anything else on your board, I’d loose the CC resistors at the input grids to prevent added hiss.
     
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  18. DJLockjaw

    DJLockjaw TDPRI Member

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    Thanks Kevin. It's a bit of a bad angle, but I do have about 1/8" between the resistors and the caps. I am a bit of a dummy when it comes to circuits, but the input grid resistors - those are the three CC resistors in the upper right, one from each input, that go to pin 2 of V1? Just so I know where to start troubleshooting if I have hiss problems.
     
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  19. Kevin Wolfe

    Kevin Wolfe Tele-Holic

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    Yes, those are the ones. You may have no noise issues. After all, it was good enough for Leo, right?
    As you’re building this amp, look at it as a learning opportunity. Get out your schematic and trace the guitar signal from inputs all the way to the speaker. I’d also suggest consulting @robrob’s website and reading through his info on ‘How a tube amp works’ for a an excellent guide to exactly what all the part do and why we tweak them sometimes.
    Uncle Doug on YouTube is another great learning experience.
    Most of all, have fun and be careful.
     
  20. DJLockjaw

    DJLockjaw TDPRI Member

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    Thanks Kevin! I'm reading through Rob's "How amps work" now (https://robrobinette.com/How_Amps_Work.htm). It's kind of neat how the value can attenuate trebles - I saw your other thread that you moved to 27k instead of 68k. I'll have to see how it sounds, and maybe adjust accordingly once I get the rest of the parts here.
     
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