5F2a-ish with Tremolo

Discussion in 'Shock Brother's DIY Amps' started by shortcircuit, Oct 20, 2019.

  1. shortcircuit

    shortcircuit Tele-Meister

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    I have a bunch of 7-pin triodes and pentodes. Time to do weird things to them.

    Schematic.jpg

    I probably should stick a 2.2M resistor between the wiper and ground of the master volume pot to maintain a ground reference for the grid of the power tube in case of wiper failure. The alternative is to hook up lug 3 of the pot to the power tube, and the wiper to the coupling cap, but that would present a variable load to the pentode, which may not be a bad thing for what I'm trying to accomplish here.

    I got the idea for the optocoupler from a thread from el34world (https://el34world.com/Forum/index.php?topic=24334.0) The tremolo tube will always be on, so there's a separate power node to isolate it from the rest of the circuit.

    Chassis (10" x 6") drilled and painted.

    Chassis.jpg
     
  2. archetype

    archetype Fiend of Leo's

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    I'm looking forward to an explanation of all that switching. I assume it's for tonal changes.
     
  3. shortcircuit

    shortcircuit Tele-Meister

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    Yep, just to mess around with the operating points of the tubes. Switch C attenuates lower frequencies when open to tighten up the tone on overdrive.
     
  4. shortcircuit

    shortcircuit Tele-Meister

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    Now, ain't that the cutest little power supply you'd ever seen!

    Power Supply.jpg
     
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  5. shortcircuit

    shortcircuit Tele-Meister

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    All done and wrapped up.

    Innards.jpg

    The optocoupler tremolo sounded great, but I had no depth adjustment. With the recommended 1M pot, I went from swampy to nothing within a tiny fraction of the turn of the pot. I tried a bunch of pots, down to 25K. With the 25K pot, I had about 1/3 of the turn available. However, because it's in parallel with the gain pot, there was basically no load on the triode, so the gain was down in the dumps. I didn't have another VT5C1 to swap in, so I converted to an output tube bias shifting tremolo, with an obligate cold bias. A 6V6 dissipates just a hair under 8W, and a 6JC5, just a bit over 10W.

    My God! It's full of switches.

    Outside.jpg

    I did the set up with a 6ER5 and a 6AU6 tube.

    TP Madness-final schematic.png

    The initial impression with the 6ER5 and the 6AU6 is that I can dial in a pretty good sounding amp, and I suspect I will be able to do so with the remaining tubes.

    The 6H*5 triodes are pretty much the same. The 6ER5 and the 6ES5 are also pretty close. So it looks like I'll have three different triodes. With the 12 pentodes, there are 36 different combinations of triodes and pentodes. Given each triode have 3 different plate loads, and each pentode have 9 different combinations of screen and plate loads, there are 972 settings to try out. Adding in the triode switch on the pentode, there is a further 324 possibilities, so a grand total of 1296 combos. This is silly.
     
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  6. symbiotic

    symbiotic TDPRI Member

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    I guess that when you get to flipping switches, you might want to keep notes! Hoo boy that's a lot of combinations.
     
  7. Nickfl

    Nickfl Tele-Afflicted

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    The lineman's splice on those diodes is a thing of beauty...
     
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  8. Nickfl

    Nickfl Tele-Afflicted

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    I see you have a remote cutoff pentode as one of your options, have you played with that one yet? Have you ever used one of those in anything else before? I've got a few deferent remote cutoff pentodes laying around from radios that I stripped and I've wondered about trying them but I have never gotten around to doing anything with them, and there seems to be very little info on them as they might relate to guitar amp applications.
     
  9. shortcircuit

    shortcircuit Tele-Meister

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    The 6BD6 tubes were leftovers from my Gibson GA-100 build. They were driver tubes for the 6L6's. They have a clean, compressed sound with a slight breakup with the gain turned up. Excellent choice for pedals, especially my home brewed big muff pi.
     
  10. shortcircuit

    shortcircuit Tele-Meister

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    :oops: That's not a lineman's splice. I'm not that skilled. It's 24 ga copper wire wound on an appropriately sized mandrel serving as a coupler.

    FLMS.jpg
     
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  11. Nickfl

    Nickfl Tele-Afflicted

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    Well, its still a pretty impressive level of attention to detail. When I have to splice two wires I just make a hook on each end and lightly crimp them together before soldering, then I cover my shame with heat shrink. ;)

    Seriously, your builds are some of the best looking PTP jobs I've seen. Most PTP builds seem to either be a rats nest or prioritize neatness over compactness and minimal wiring runs. You manage to have both and every time I see one of your build threads it inspires me to keep trying to up my layout game.
     
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