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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


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ramon68
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    ST70 too bright...why?

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    tygr1


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    ST70 too bright...why? Empty ST70 too bright...why?

    Post by tygr1 Fri Dec 12, 2014 7:50 pm

    My new to me ST70, recapped and with VTA driver board sounds a little too bright to me. What ever has happened to that "tube warmth" I was expecting? Could it be the new EH tubes?

    I run it alone with just my Sony ES CD player with output level control and it's too bright. I run it with my Magi all tube preamp and Denon DVD player and it's still too bright for my tastes.

    Any insight? See pics on page 2 of this thread.


    Last edited by tygr1 on Wed Dec 17, 2014 7:59 am; edited 1 time in total
    sKiZo
    sKiZo


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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by sKiZo Fri Dec 12, 2014 8:02 pm

    New tubes can take a while to break in. Give it time before getting too worked up. They should be about as good as they'll get after at most 100 hours.

    You want to experiment, try switching out the driver tubes. Lots of possibilities in the 12AU7 family. My ST120 was too bright for the room, and I went with a nice triplet of Westinghouse 5963's ... perfect! I also tried some 12BH7a's, and those were too dark.



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    tygr1


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    Post by tygr1 Fri Dec 12, 2014 8:34 pm

    Thanks for that Skizo. I think I'll try a little tube rolling.
    Maintarget
    Maintarget


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    Post by Maintarget Fri Dec 12, 2014 10:58 pm

    As sKiZo has mentioned I would resist any tube rolling until you have at least 100 hours if not more you might be surprised how much the sound actually changes in that time.
    I'd give a 12BH7 a try in the center position if you're still too bright after break.
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    audiobill


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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by audiobill Sat Dec 13, 2014 5:49 am

    Look at your speakers and speaker/room setup, too.

    Dampen first reflections.......
    corndog71
    corndog71


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    Post by corndog71 Sat Dec 13, 2014 11:03 am

    I know one easy tweak that will also do the trick. Change the output caps to Clarity Cap ESA series.  They're a little darker in the upper treble region yet still offer a very clear and detailed midrange and low end.  Jolida uses them in their upgrades as do other high end companies. They're not crazy expensive either.

    That means giving up on those sexy Russian caps but the ESA's aren't too ugly.  

    http://www.partsconnexion.com/capacitor_film_claritycap_esa_630.html

    Oh yeah, what audobill said. Cover up those first reflection points. ATS Acoustics sells some really nice panels that work very well for this.
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    tygr1


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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by tygr1 Sat Dec 13, 2014 12:21 pm

    They are 8 ohm single driver full range Audio Nirvana speakers with no crossovers.
    arledgsc
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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by arledgsc Sat Dec 13, 2014 12:59 pm

    Give the new components and your ears some time to adjust.  It took six months for my ST-120 to settle down after recapping.  I do though find the recapped, well broken in ST-120 has slightly more highs than my expensive 250W/ch. transistor amp that is +/- 0.1dB flat in the audio band.   But I can only listen for a short time to the sand amp before start missing the airy highs and switch back to valves.  But ultimately depends upon the tube types used.  Try some Mullard CV4003s either center or phase inverter position.  Those tubes will definitely roll off the highs.   Different tubes have been a tone control for tweaking the sound I like.  Has been expensive though rewarding experience.  However I would not have been as delighted today with the ST-120 without exhaustive tube rolling.  Give it time and don't be afraid to experiment.  Of course if your amp has a problem (like wrong value caps) then needs to be rectified.
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    ramon68


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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by ramon68 Sat Dec 13, 2014 1:56 pm

    Does your full range driver have a rising high end? From what I've read, a lot (read most) of them do. There is a cheap tweak to fix that on Transcendent Sound's website under the heading diy speakers.
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    tygr1


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    Post by tygr1 Sat Dec 13, 2014 2:53 pm

    It's not the speakers. The only thing that's changed in my setup is the amp.
    sKiZo
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    Post by sKiZo Sat Dec 13, 2014 4:49 pm

    I'd still try rolling to a darker driver tube first. That can completely change what you're hearing. I seem to remember you mentioning that this wasn't a problem with the old system setup?

    That don't work, then do some room tuning - never a wasted effort as even a room that you were happy with can usually sound SO much better with a little effort. Hardscaping first to kill hard reflections and the major issues, the a good parametric EQ works wonders to fine tune the room.

    My favorite test for high end problems is Norah Jones Come Away With Me. Her voice and piano would just pierce the ears until I tamed the hard reflections off the ceiling. Simple fix too ... tacked some memory foam carpets up there ...

    ST70 too bright...why? Ceiling-carpets-001

    They weigh next to nothing and set me back less than $20 for both. Easy to do, and really killed the shrill. She's licking my ears now and I keep wanting more ...  ;-}

    PS ... I got a lot of real nice tubes off that auction site ... some well established sellers on eBay and you don't have to wait for the tubes to break in. I figure I average about $10 a pop.
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    tygr1


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    Post by tygr1 Sat Dec 13, 2014 5:12 pm

    Thanks again Skizo! I'm taking your advice and have already ordered some tubes.
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    tygr1


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    Post by tygr1 Tue Dec 16, 2014 7:54 pm

    OK, does anyone see anything out of the ordinary here.

    ST70 too bright...why? DSC_0001_zpse6206adc

    ST70 too bright...why? DSC_0003_zps00378f22

    ST70 too bright...why? DSC_0004_zpsca39f943
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    zx


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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by zx Wed Dec 17, 2014 1:17 pm

    Yes....Ck the b+.........I have my old hhshott 355 tuner-preamp running on one of my minny Varics
    I can give more topend just by tuning the B+down ....an bring the B+up an get better mids...
    All so with the B+ being to high the heaters may be to high....hhscott ran there input tube at 5.5v....some of the best sound I have had in 50 years of tubes....heaters  to high can also make the topend too hot....bring the B+ down brings the heaters down.....
    The Varic not only give me what ever sound I wont....it saves older partes that too me can still sound better than some new parts....have fun with tubes




    Thanks for the site Bob......
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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by Guest Wed Dec 17, 2014 1:42 pm

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    Last edited by PeterCapo on Wed Dec 02, 2020 5:38 pm; edited 1 time in total
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    tygr1


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    Post by tygr1 Wed Dec 17, 2014 1:53 pm

    Thanks Peter, I am very familiar with high voltage safety practices. Just new to tubes and not sure where to get the correct B+ voltage. Also, can it be checked with no speaker load on the amp?
    peterh
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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by peterh Wed Dec 17, 2014 2:00 pm

    tygr1 wrote:Thanks Peter, I am very familiar with high voltage safety practices. Just new to tubes and not sure where to get the correct B+ voltage. Also, can it be checked with no speaker load on the amp?
    Always have a load on tubeamps, speakers or a resistor.
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    tygr1


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    Post by tygr1 Wed Dec 17, 2014 2:05 pm

    Thanks PeterH, I thought so.
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    zx


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    Post by zx Wed Dec 17, 2014 2:38 pm

    You can ck you B+ right at pin 8 of the 5AR4...Or the frist cap after the Choke...should be the multy cap ....also .Ck see what the B+ that feeds the driver board....looks like the red wire after the res.on the cap..............




    thanks for the site Bob.............
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    tygr1


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    Post by tygr1 Thu Dec 18, 2014 7:56 am

    Well my meter is rated for 500v and it shows an overload when connected to pin 8 of the rectifier tube. I have already ordered another meter rated for 600v. What B+ voltage should I see? If I'm reading voltage in the right place for the driver board, I'm only seeing 15.2v. What should that voltage be?

    Thanks so much zx.
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    ST70 too bright...why? Empty Re: ST70 too bright...why?

    Post by Guest Thu Dec 18, 2014 11:01 am

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    Last edited by PeterCapo on Wed Dec 02, 2020 5:39 pm; edited 1 time in total
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    zx


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    Post by zx Thu Dec 18, 2014 2:51 pm

    Well the stock ST70 PIN 8 BZ34 435 B+ to grond.....so your way high....if you get over 500b+ I would turn it off...I say 450-70 at most an thats to high.....Free Dynaco tube schematics ...go here Bob has help us all with great info...
    PS next metter.....nothing less than 1KV dc.....save you a lot of time an give more head room....hehe....not spending you $$
    ...ever one need a good metter an iorn...if you working with tubes....have fun



    Thanks for the site Bob...............................
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    tygr1


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    Post by tygr1 Thu Dec 18, 2014 3:27 pm

    Yeah, the owner's manual says 435v there too. I'm just not trusting my meter right now (maybe the batteries) so I'm going to wait for the new one and check B+ again.

    Thanks everyone.
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    Post by Guest Thu Dec 18, 2014 3:32 pm

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    Last edited by PeterCapo on Wed Dec 02, 2020 5:39 pm; edited 1 time in total
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    tygr1


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    Post by tygr1 Thu Dec 18, 2014 3:42 pm

    Yes, it's a 3A 250v slo blo.

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