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    A new VTA-ST70 build!

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    corndog71

    Posts : 453
    Join date : 2013-03-19
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    A new VTA-ST70 build!

    Post by corndog71 on Fri Jun 20, 2014 2:09 pm

    Well, so far it's just an idea in my head and on paper. It's going to be point to point like my previous efforts. 360uF total power supply capacitance via Clarity Cap TC caps. Russian signal caps. (As much as I like Clarity MR series caps I think I like the Russian caps a little more. Similar detail but slightly warmer.) Hammond aluminum box 17x13x2".

    This is going to take me a while to put together as life is always competing for my money.

    I sketched this out last night on my ipad.






    Captain Coconut

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    Re: A new VTA-ST70 build!

    Post by Captain Coconut on Fri Jun 20, 2014 2:16 pm

    Good stuff Corn. How do you "sketch" on an iPad?

    corndog71

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    Re: A new VTA-ST70 build!

    Post by corndog71 on Fri Jun 20, 2014 3:05 pm

    Captain Coconut wrote:Good stuff Corn. How do you "sketch" on an iPad?

    I have an app called "Paper" by 53. It's a very unique sketching app that I've really grown to love.

    Here's a video of someone else using it to sketch an eye. My sketching is a bit more free flow.


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    Re: A new VTA-ST70 build!

    Post by Guest on Fri Jun 20, 2014 3:13 pm

    corndog71 wrote:Well, so far it's just an idea in my head and on paper.  It's going to be point to point like my previous efforts.  360uF total power supply capacitance via Clarity Cap TC caps.  Russian signal caps.  (As much as I like Clarity MR series caps I think I like the Russian caps a little more.  Similar detail but slightly warmer.)  Hammond aluminum box 17x13x2".  

    This is going to take me a while to put together as life is always competing for my money.  

    I sketched this out last night on my ipad.






    Nice looking layout.
    I'm sure you already know, make sure you keep power tube wiring away from driver tube wiring, lower any possible interference. The on/off power switch, right between hot transformers and might be difficult to get to.

    corndog71

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    Join date : 2013-03-19
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    Re: A new VTA-ST70 build!

    Post by corndog71 on Fri Jun 20, 2014 3:48 pm

    MontanaWay wrote:
    Nice looking layout.
    I'm sure you already know, make sure you keep power tube wiring away from driver tube wiring, lower any possible interference. The on/off power switch, right between hot transformers and might be difficult to get to.

    The drawing isn't completely to scale. I did the same thing for my ST120 and have no trouble accessing the power switch. With more space between them the output transformers don't really get hot. Just the power transformer gets hot.


    sKiZo

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    Re: A new VTA-ST70 build!

    Post by sKiZo on Fri Jun 20, 2014 4:53 pm

    Looking good! Just don't be concerned if the final product doesn't look anything like the sketch. My projects tend to suffer some serious design drift as a build progresses. Usually for the better.

    Same concern here though, mixing driver an power tubes. Maybe use small gauge microphone type  wire? Single conductor with a tight shield should cut down on any potential noise a bunch. I'd also consider caging the sockets underneath, putting metal between them ... I'd think the solder tabs on those would be more sensitive than the point to point attachments.


    corndog71

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    Re: A new VTA-ST70 build!

    Post by corndog71 on Fri Jun 20, 2014 5:02 pm

    I can't imagine having driver tubes close to power tubes being a problem.






    sKiZo

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    Re: A new VTA-ST70 build!

    Post by sKiZo on Fri Jun 20, 2014 5:57 pm

    Not saying it's necessary, just saying I'd be concerned, and it wouldn't take much to design some isolation into the build.

    McIntosh 275 seems to do that with a massive wall of capacitors ...



    In your case, I expect a bit of metal would suffice.

    Or not ... your build, your call.

    PS ... reminds me of the isolated ground plate I was planning to put in mine. Remember that?



    I let you all talk me out of it, and now I'll never know ... Still makes a nice back scratcher ...

    Maintarget

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    Re: A new VTA-ST70 build!

    Post by Maintarget on Fri Jun 20, 2014 10:08 pm

    Twinkie the Kid,
    SkiZo your certifiable that's why I look forward to your post's! affraid  lol!

    corndog71

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    Re: A new VTA-ST70 build!

    Post by corndog71 on Sat Jun 21, 2014 12:46 am

    Alright, I can concede when I'm wrong. It turns out the power tubes can couple with the driver tubes causing instability if they're too close.

    Back to the drawing board. Which is fine. I had multiple layouts in mind.

    sKiZo

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    Re: A new VTA-ST70 build!

    Post by sKiZo on Sat Jun 21, 2014 1:24 am

    I still think the plan is workable ... do tin dividers around each driver socket and twist the wires outside the boxes for isolation? Common practice with power supply and tuner circuits anyway. Wouldn't need extra holes - just fold in tabs and attach to the socket screws. Wouldn't even need to be all that tall ... just so there's no straight line of sight between circuits ...

    Definitely be unique if you could make it work ...

    ** Twinkie's sort of an inside joke ... I'll leave it there for a couple or three days just to show folk what avatars not to post ...  jocolor 

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: A new VTA-ST70 build!

    Post by zx on Sat Jun 21, 2014 7:25 am

    ** Twinkie's sort of an inside joke ...On who Bob??....
    I'll leave it there for a couple or three days just to show folk what avatars not to post

    Looks like some here cant use E-mail.....if thay wont to talk about ...there bad hair day....geees

    Now as For corndogs amp theres no right are left....his amp he posted a pic..... looks great too me.........hay he new to use two chokes in a two ch amp....most other dont...just saying.
    this is a Diy site....I think....you wont no if you dont go!

    Thanks for the Tube site Bob..........

    corndog71

    Posts : 453
    Join date : 2013-03-19
    Location : It can get windy here

    Re: A new VTA-ST70 build!

    Post by corndog71 on Thu Jun 26, 2014 11:39 am



    Here's where I'm at now design-wise. I have an internal layout down but as I said before this is a going to take a while to gather up all of the parts. I'm waiting to receive a new Bottlehead Smash preamp kit which will be my next project.

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: A new VTA-ST70 build!

    Post by zx on Thu Jun 26, 2014 1:39 pm

    Bottlehead .....lot of people like there amps an pres.....use low V tubes in some of the pre...looks good on paper....
    I have never got to hear any of there offerings..... Crak.. OTL looks cool.

    youll get the amp lay out in time....you other Diy work looks great,have fun with tubes.....




    thanks for the tube site Bob......

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: A new VTA-ST70 build!

    Post by sKiZo on Thu Jun 26, 2014 1:59 pm

    I like that ...

    I take it those are T/P switches by the bias pots?

    I'd also add a common test point. That's handy for the VOM ...

    Twere me, I'd also go with real pots instead of the board mounts. Problem is deciding what pots to go with. I tried some of the cheepo Chinese jobs and had one go open and run away on me. Currently running some Fender 50k's, but those aren't a true linear and get a bit twitchy in the correct range. Easy fix would be to just reverse the wiring, but I get confused enough when up really means up.  geek 

    I did pick up on a set of the "bourns" multiturn pots off that auction site.





    Even came with the special knob that counts turns. They feel solid and test well (standalone anyway) with a VOM ... they DO come up a bit short of full range on average (0.3 - 48.5k), but certainly within the stated tolerance. Smooth progression through the range and rock steady over time. I figure to swap those in next time I drag the beast down to the bench.

    corndog71

    Posts : 453
    Join date : 2013-03-19
    Location : It can get windy here

    Re: A new VTA-ST70 build!

    Post by corndog71 on Thu Jun 26, 2014 3:07 pm

    sKiZo wrote:I like that ...

    I take it those are T/P switches by the bias pots?

    I'd also add a common test point. That's handy for the VOM ...

    Twere me, I'd also go with real pots instead of the board mounts.

    Yep on the T/P switches.  In the earlier version they would've been behind the tubes.  

    The Hammond boxes often have a little hole in the corners where the sheet metal was bent. I use those for the black VOM lead. Or sometimes I just press hard anywhere on the box. Seems kinda redundant to add a ground test point.

    I like the stock pots.  I haven't had any problems with them.  I kinda prefer them recessed behind a hole vs a surface-mounted knob that ignorant hands might like to play with.

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