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Next up a PSE Flea powered amp - the Mighty 71-A

Discussion in 'Tube Audio' started by analog addict, Feb 19, 2018.

  1. Ziradog

    Ziradog AK Subscriber Subscriber

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    +1
     

     

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  2. analog addict

    analog addict Glory or Death!

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    Cleaning up a vintage terminal strip to populate the underside of the chassis. I prefer vintage terminal strips, since they tend to be higher quality then the current Rat Shack type stuff.

    [​IMG]Untitled by Analog Addict, on Flickr

    Have the underside of the chassis populated. The second 5V filament transformer is not gonna be secured in until I can get the inputs and outputs wired up due to ease of work considerations.

    [​IMG]Untitled by Analog Addict, on Flickr

    Unfortunately, the Honey Dew list is calling, so amp building will have to be put on hold for awhile....
     
    drtool likes this.
  3. s-petersen

    s-petersen Scott

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    :lurk: watchin'
     
  4. Tubeglowpio

    Tubeglowpio Active Member

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    336
    Location:
    AZ
    Very nice, cant wait for impressions. Were you able to post a schematic for the 45 amp? I'm about to pull the trigger on a 2a3 schematic but a parallel 45 might do he trick.
     
  5. analog addict

    analog addict Glory or Death!

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    Trying a different process this time. Instead of starting with the power supply, I wired up most all the grounds, including the PS caps.

    [​IMG]Untitled by Analog Addict, on Flickr

    Here's where the other 5V transformer will go once the signal side wiring is in....

    [​IMG]Untitled by Analog Addict, on Flickr
     
  6. analog addict

    analog addict Glory or Death!

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    Progress. PS is mostly done, along with the VR circuit. Starting to wire the high voltage side up, but realized I may need a couple of 750 ohm/12W resistors for the cathode circuit. Oh well....

    [​IMG]Untitled by Analog Addict, on Flickr
     
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  7. analog addict

    analog addict Glory or Death!

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    Almost done. Mocked up the final configuration and will be taking some of the superfluous terminal strips out. Also need to run the parallel wiring on the 71A filament and plate connections. The Jensen coupling caps will go in last.

    Soon....

    [​IMG]Untitled by Analog Addict, on Flickr
     
    x3workshop likes this.
  8. Mike Stehr

    Mike Stehr Poverty Audio

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    Nice work.
     
  9. s-petersen

    s-petersen Scott

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    If those large resistors get hot, I think the heat may not be so good for the caps.
    I think it looks great otherwise.
     
  10. analog addict

    analog addict Glory or Death!

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    Yeah I hear you. That's the common cathode resistor/capacitor set up for the three 71-As. I happened to find a dual resistor of the right value in the box of power resistors. The plan is to bend them away from the resistor(s) towards the bottom plate once everything is soldered into place. Also, hopefully the heat will rise away from the caps once in operating position....

    [​IMG]Untitled by Analog Addict, on Flickr
     
    Pio1980 likes this.
  11. s-petersen

    s-petersen Scott

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    I was talking about the green and white ones on the other caps, unless they are temporary.
     

     

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  12. analog addict

    analog addict Glory or Death!

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    Hmmm. I see what you mean. I'll have to check how much power is being dissipated in those resistors. Thanks for the heads up
     
  13. analog addict

    analog addict Glory or Death!

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    Why amp building is a labor of love for me....

    [​IMG]Untitled by Analog Addict, on Flickr

    Or an expression of my OCD/ADD/other abby-normal tendencies and habits.

    [​IMG]Untitled by Analog Addict, on Flickr

    Well, didn't have much time today, given that mulch shoveling took precedence over amp building on SWMBO's list. So, all I got to was the plate wiring from the OPT. Still moving forward however...

    [​IMG][​IMG]Untitled by Analog Addict, on Flickr
     
  14. analog addict

    analog addict Glory or Death!

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    Got a little more ambitious. All that's left is one of the 6SN7 sockets to wire up. Should be done by Sunday

    [​IMG]Untitled by Analog Addict, on Flickr
     
  15. Blueglow

    Blueglow Eternal Tinkerer Subscriber

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    Looking good!
     
  16. analog addict

    analog addict Glory or Death!

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    Heh, After finishing it up, I started to go back through it for mistakes, and for one thing, if you look at the pix, the HV line is coming off one of the rectifier plates, not the filament. Also, somehow I have the wrong PT in this thing, only giving me 195V at the first filter instead of 300V+. Guess it's what happens when you paint all these things black and obscure the markings. Luckily, I have the right PT sitting around, so out comes the old one and in goes the new one. Sigh... I need to build more often cause I am seriously out of practice...

    Anyway, this is what it looked like on the first go round. Let's see what it looks like after round # two...

    [​IMG]Untitled by Analog Addict, on Flickr
     
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  17. analog addict

    analog addict Glory or Death!

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    Drilled a few new holes and changed out the PT. Barely finished it in time to throw it in car and haul it across town to Dennis’ shop. He went over it and it turns out I had brain farted and forgotten both sets of grid leak resistors. Oops. That and a solder joint or two and we were up and running.

    [​IMG]Untitled by Analog Addict, on Flickr

    Threw in the good set of tubes and Oh Boy! does she sound good...

    [​IMG]Untitled by Analog Addict, on Flickr

    [​IMG]Untitled by Analog Addict, on Flickr

    Dennis said the second he heard the needle drop he knew it was going to have a strong bottom end, and it has glorious bass for a 2.5 wpc toob amp. However, we looked at the square wave, and it's clean up to 5 watts, which IIRC, means I'm looking at 3 db of dynamic headroom.
    Not bad for almost century old toobs...
     
    Last edited: Apr 27, 2018
    x3workshop, fredgarvin, RUmad and 5 others like this.
  18. s-petersen

    s-petersen Scott

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    It Lives!:banana:
     
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  19. analog addict

    analog addict Glory or Death!

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    Oh it more than lives, it ROCKS!!! I've got it on the shop system running the Khorns via a Mc MX-110z. I need to listen to it a bit more, but I'm starting to wonder if this is the best sounding amp I've built. Dennis and I were talking about it, and he laughed and asked me if I knew which amp was the best one the amp builder ever built. I guessed right - the one he/she just finished....

    [​IMG]Untitled by Analog Addict, on Flickr

    [​IMG]Untitled by Analog Addict, on Flickr
     
  20. wlgrant6

    wlgrant6 AK Subscriber Subscriber

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    Amazing. Nice build.. Bill
     

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