Matchless Spitfire Clone

Discussion in 'Building the Classics' started by RiverRatt, Oct 25, 2017.

  1. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    I just finished a Spitfire build using an old Hammond organ amp chassis and transformers. I left the heater string wired up but that’s about all that was stock.

    I followed the info on the Watts Tube Audio site, but I changed it over to use 6CM6 output tubes. They are a close cousin to the infamous and expensive 6973 tube used by Supro. I can sub a 6973 and 6CZ5 directly.

    This thing has massive balls and a great overdrive tone. I’m trying to get a decent clip of it. I’m a big fan of the 6CM6. I used it in a little single-ended amp and it had the same qualities there. Kinda like a KT66 in a 9-pin bottle. It’s a fairly easy sub for an EL84 as long as the plate voltage isn’t too high (these are running at 350VDC).

    Here it is. I need to clean it up and make it pretty.

    [​IMG]

    [​IMG]
     
    Crab, dptone5, soundboy57 and 10 others like this.
  2. liontato

    liontato Well-Known Member

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    Awesome! Would love to hear it!
     
  3. coldengray

    coldengray Active Member VIP Member

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    Nicely done. I did One of these has a scratch build and made some modifications to the circuit that I think improved it at least in my opinion. I lowered the V1 play resister to 100 K across the paralleled triode. It's very clean and chimey with single coils but when cranked has great grind with my Strat. That change makes humbuckers sound awesome without getting too fizzy. As part of this change I upped the PI entrance caps to .015 and the PI Output caps to .033uf. I also added a Cut control that works nicely.
     
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  4. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    Here's me playing some chords with the SG. The first part is first succssful power-on, the second part is after I played with the brite cap value ad added a second brite cap on the master volume. I recorded this with my iPhone so it isn't great but you can hear the tone those 6CM6 output tubes bring to the table. Did I mention that I love those tubes? :naughty:

     
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  5. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    Thanks, I'm still dialing it in. I haven't had any problem with fizz and humbuckers, but it was a bit muddy at first. My strat sounds awesome - clean and chimey or fat and creamy. Mmmmmmmm.
     
  6. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    Still dialing it in, but it’s almost there. I ended up dropping the B+ down to 325VDC. The output tubes were redplating even after biasing them more conservatively. I changed out the dropping resistor on the PI node from 22k to 15k as they lost around 25v from the lowered B+.

    I changed the coupling cap on V1 from 22nf to 4n7 to clear up the mud, and added a 150pf cap across the master volume. It’s really, really sounding good.

    Sorry to bore y’all to death but this is my first push-pull amp and I’m astonished at how well it’s turned out. It’s literally like I cleaned out my junk parts and found a boutique amp hiding in there. I’m really glad I went with the Spitfire and not the Lightning or an 18 watt clone.

    If anyone has a good idea for a head cabinet for it, I’d appreciate any suggestions. I’m working on a tight budget. Hell, I don’t think I have more than $75 in the amp as it sits.
     
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  7. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    I added a half power switch courtesy of the Ceriatone Creme Brûlée.

    [​IMG]
     
    kingmlg likes this.
  8. kingmlg

    kingmlg New Member

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    Nice work. I built a spitfire about five years ago. I also used old organ amp parts.
    I used the schematic from ceriatone. It sounded so good from startup, I haven't changed one thing. I put it in a empty music man cab with original speaker. This baby sounds good with humbuckers or single coils. I use it for bar gigs and haven't had any problem at all.
    I have a pair of 6973's from the donor amp.
     
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  9. liontato

    liontato Well-Known Member

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    Sounds good! Nice and thick! I don’t like wispy thin tone. This sounds great!
     
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  10. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    I made several changes that I later reversed because they took too much away from the tone. I realized a little while into the changes that I was trying to voice the amp to that one particular cabinet, which is an oversized 1x12 closed back cabinet. I think it has an Eminence Legend in it, which I really should be thinking about changing. There’s a guy locally who has an EVM-12L is like to try.
     
  11. allwheelz

    allwheelz Well-Known Member

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    That thing looks sinister!!! Like rusted chains and razorblades, torture chamber kind of darkness!! VERY cool!!!
     
  12. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    LOL I don't know about all that. I'll admit I could have been cleaned up some. Transformer rust is usually best left alone though. I guess it does have a steampunk vibe to it. I am probably going to clean the face of the chassis and paint it with this dark tinted poly I have. I did another amp like that and I loved the look.

    [​IMG]
     
  13. RiverRatt

    RiverRatt Well-Known Member VIP Member

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    Got some great 6973's for the amp from kingmlg. These things sound AMAZING! Thanks brother.
     
  14. kingmlg

    kingmlg New Member

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    Your welcome RR. I'm glad your enjoying them.
     
  15. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    Nice done RiverRatt! A superb project ☺️
     

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