Modern Balanced Tube Amp Build

  1. SonicTrance
    So I'm in the process of building version 2.0 of this amp. Now with separate psu chassis and signal chassis, featuring 6C8G input and 47 output tubes. Thought I'd post a bunch of in progress pics of the build for anyone interested. It'll be like a build log.

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  2. SonicTrance
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    Here's where I'm at now. Psu chassis done, will probably need to adjust some R's in the filters but other than that all done. Here in the signal chassis I've mounted input stage gyrators and B+ decoupling caps as well as one parafeed cap. More to come.
     
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  3. gug42
    Wahou really nice jobs. Beautifull works :) Hope one day to be capable of doing a so nice work :wink:

    Where did you buy the enclosure for toroidal transformers ?
     
  4. SonicTrance
    Thanks!
    I got the tranny covers from some Chinese ebay seller, of course :)
     
  5. SonicTrance
    Wiring up the 6C8G's

    IMG_0972.JPG
    Lots of resistors in the sockets. These are 100ohm stoppers for grids, anodes and cathodes.
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    Put a 400mVpp signal through the input stage and this is what came out. One phase is grounded so the µ36 gets cut in half to µ18. Looks very good so far.
    IMG_0974.JPG
     
  6. SonicTrance
    Grid drivers with 0.25µF KBG coupling caps are in and tested! Works as planned. Also hooked up the VU-meters. Pretty hard not to have it look messy with all these wires! Will try to tidy up a bit later on. Next step will be gyrators and voltage reference for the #47 output tubes.

    IMG_0977.JPG
     
  7. MrCurwen
    It looks clean enough. Remember parallel wires are just extra parasitic C in the circuit!

    What P to g2 resistor value are you going for with the 47's?
     
  8. SonicTrance
    Think I’ll start off with 1k and if there’s oscillation move up to 10k, or something in between. What do you suggest? Maybe go for 10k from the start?
     
  9. SonicTrance
    Been soldering for two days straight. All that’s left now is output wiring. Everything else is in place with all good voltages and nice sine wave at the output. Can’t wait to listen to it for the first time!

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    Maxx134 likes this.
  10. MrCurwen
    Looks very good!

    How's the noise floor? I'm thinking mainly considering the filament supplies on the 47's.

    The OT should eat most of it away if there's any, but it's one of the possible problem areas.
     
  11. SonicTrance
    So, here's how the internals looks finished! The ice cream sticks on top of the large parafeed caps are there to make the caps level with the bottom cover, to ad support. Amp sounds fantastic, I'm very happy with it.

    Signal chassis:
    IMG_0991.JPG

    Psu chassis:
    IMG_0993.JPG

    Will take some nice pics of the exterior and update first post later.
     
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  12. gug42
    nice works :)
    I like to see your post and photos :)
     
  13. Maxx134
    From looking at all the point-to-point wiring,
    This would have taken me countless sleepless days worrying I miss a solder spot! Lol
    I like how you used the resistors leads instead of more wiring, or making a Circuit Board.

    Wow just excellent work beyond normal.
    Nice big block caps you have on sides.
    They look like industrial or type you see in high voltage lamps.

    Nice touch using what looks like lamp sockets for connecting between PSU and amp, right?
    :)
     
    Last edited: Dec 11, 2017
  14. SonicTrance
    Thanks gug42!

    I build each module outside the case before I install (glue) them in to place. Makes it pretty easy.
    :)

    Yes! I think point to point is the way to go.

    Thanks Maxx!
    Those are the 4µF 400V KBG parafeed caps. And yes, they're huge, lol.

    No, I use two octal sockets to pass what's needed from the psu to the signal chassis.
    IMG_0918.JPG
    I've the filament supplies for the 47's in one octal socket. Four local grounds and four hot wires.
    B+ for the LTP, B+ for the power buffer, B-, 12V for the meters, chassis ground and 6.3V heaters for 6c8g's in the other.
    IMG_0952.JPG :)
     
  15. MrCurwen
    Yes, so much more easier to troubleshoot and mod. In my opinion there's no way to do really good experiments without P2P.

    This is how all amps and electronic instruments were built in the golden days of tubes. Once you get enough practise, it's much easier than dealing with a PCB.

    Prettiness of the layouts do of course vary a lot, Sonic is very good at 3D layouts.

    They are in fact industrial types. Mostly military, "EMP resistant".

    The outer insulation makes the wire look very good. I just twist the individual wires around each other and leave it like that. Oftentimes I use different colours for the wires...
     

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