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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


    my own VTA70 amp

    tubes4hifi
    tubes4hifi
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    Post by tubes4hifi on Sat Sep 21, 2019 10:34 pm

    not the greatest photo, but I wanted to give you an idea of how you can make your amp look different.
    This is a standard VTA70 mounted in my usual preamp chassis, cost of chassis and faceplate around $200.
    About $50 more with the VU meters and dual gain controls and input selector.

    The lower photo is another custom VTA70 amp I built a couple years ago.

    my own VTA70 amp Amp3

    my own VTA70 amp VTA80

    Dave_in_Va
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    Post by Dave_in_Va on Sun Sep 22, 2019 11:08 am

    Roy, so you mean you've got an SP 14 AND an ST70 inside that amp in the top pic?

    The one in the bottom pic is nice. Do you sell that top plate separately? If not, I bet many do-it-yourself wood workers would go for that.
    tubes4hifi
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    Post by tubes4hifi on Sun Sep 22, 2019 1:06 pm

    Hi Dave,
    no preamp in there, just a source selector and volume control.
    The amp has enough gain to handle most line level inputs.
    I'm always doing custom stuff for customers.
    Roy www.tubes4hifi.com
    corndog71
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    Post by corndog71 on Mon Sep 23, 2019 1:31 am

    I really like the top one! Got an interior shot?
    tubes4hifi
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    Post by tubes4hifi on Wed Sep 25, 2019 12:31 pm

    sorry CornDog, no photos, and the amp is out on loan right now, but here's a couple shots of similar amps I'm starting on . . .
    as you can see, an ST70 (or ST120) amp chassis can drop right into this chassis, and the top cover is 6" high so it all fits nicely
    On lower powered amps, using small output tubes, a 5" tall chassis is fine. Makes a nice match for an SP14 preamp . . .
    my own VTA70 amp Amp11
    my own VTA70 amp Amp12
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    speedyk

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    Post by speedyk on Thu Oct 10, 2019 8:06 pm

    Does that case have enough ventilation?
    tubes4hifi
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    Post by tubes4hifi on Thu Oct 10, 2019 8:24 pm

    yes, plenty!
    Mr C
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    Post by Mr C on Fri Oct 11, 2019 10:34 pm

    I'm real new and a amateur at this. So what does the VU meters indicate? When the needles are at 0 what does that mean? My experience with VU meters has always been on tape decks.
    tubes4hifi
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    Post by tubes4hifi on Sat Oct 12, 2019 3:09 am

    VU meters have been commonly used in audio equipment for over 50 years, if you want a good explanation read the article on Wikipedia
    https://en.wikipedia.org/wiki/VU_meter
    a level of zero VU is 1.2vrms, which is about the level of modern line outputs, and is enough to drive most amplifiers to their full output.
    So similar to use on a tape deck, where you want to set the level not to exceed a signal level that will cause distortion
    Mr C
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    Post by Mr C on Mon Oct 14, 2019 12:37 am

    Thanks for the link.  I was wondering.  I've seen different meters used in these amps.  There is one I've seen pictures of and the meter is labeled mA.  And watt meters.  So I'm curious what they indicate and how interpret what they indicate.  And if I where to add meters what would be the must useful.
    Wotan
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    my own VTA70 amp Empty Bottom photo transformers

    Post by Wotan on Mon Oct 14, 2019 10:37 am

    In the bottom photo, did you replace the standard E-core transformers with toroids?  Or are those just covers?
    tubes4hifi
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    Post by tubes4hifi on Mon Oct 14, 2019 12:53 pm

    Mr C
    meters labeled ma are to measure milliamps, usually the current thru the output tubes.
    meters labeled watts are to measure the output power in watts
    meters labeled VU are to measure volume units

    WOTAN,
    in the 2nd photo, those are very high quality toroid output transformers, and a 3rd internal toroid used for power
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    tubesman

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    Post by tubesman on Tue May 19, 2020 8:32 am



    Could you share who the output toroids came from? Model number and brand?
    tubes4hifi
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    Post by tubes4hifi on Tue May 19, 2020 12:21 pm

    the output toroids are sourced from Toroidy.pl in Poland, super high quality and great prices, takes 4-5 weeks to get them
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    tubesman

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    Post by tubesman on Tue May 19, 2020 12:32 pm

    tubes4hifi wrote:the output toroids are sourced from Toroidy.pl in Poland, super high quality and great prices, takes 4-5 weeks to get them

    Cool, thanks for the data, I am familiar with them. Glad to hear you like them. I have two quick questions, what model number is it and are you using an Auto-bias board?  Thanks again!

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