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    Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

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    oatstao

    Posts : 7
    Join date : 2011-04-28
    Age : 42
    Location : freedom islands pacific west coast canada

    triode mode- bridged mono

    Post by oatstao on Sun Oct 23, 2011 3:59 am

    thanks for sharing this fabulous circuit.
    Very handy.

    I'm currently using my DYN-stereo 70
    it can run Stereo fine but I'm augmenting it
    with a stereo Yamaha Natural Sound on my desktop
    to run a single JBL 4311 on the floor for the lowend.
    I'm running the JBL in bridged mode (connecting one speaker
    to the two positive terminals on the DYNaco 70)

    Is there a benefit to adding the triode scheme to that setup?
    Sorry if it's a redundant query.


    tubes4hifi
    Admin

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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by tubes4hifi on Sun Oct 23, 2011 8:52 pm

    triode mode is normally used more to enhance midrange than for bass, and it would provide less power for bass,
    so I'd suggest you continue to run it as is

    burnedfingers

    Posts : 31
    Join date : 2009-05-06

    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by burnedfingers on Sat Jan 07, 2012 6:56 am

    I modified my first stereo 70 with a triode/ult switch probably 10 yrs ago. I used a single switch with 12 connections so that I didn't have to switch two switches. To be honest here I cannot see the logic behind using two switches instead of just one. Have heard comment about triode vers ult operation many times and I guess in up to the person listening to figure what he or she likes or dislikes. My personal opinion is the driver board and specific additions that a person has added to their 70 makes a difference in what the final tonal quality of the amplifier is. My 70 with the VTA board in it achieved 40 watts into an 8 ohm load at the onset of clipping with a 1K sine wave. My standard 70 at the same time with the same testing conditions achieved 30 watts. In running triode the power I calculated was down about 50-60%. So 30 watts to 15watts is a 3db drop. The average person sometimes can hear a 3db difference. There is a loss of bass in my opinion but the midrange blooms a little more. With some music I like it like jazz for example it was nice. I do not however believe in throwing the switch on the fly because any switch you use in that location is NOT rated for the voltage it sees so my recommendation as well as others on other forums is to not throw the switch on the fly for safety sake.

    Bob Latino
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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by Bob Latino on Sat Jan 07, 2012 11:25 am

    Re: > "I modified my first stereo 70 with a triode/ult switch probably 10 yrs ago. I used a single switch with 12 connections so that I didn't have to switch two switches."

    The purpose of the two switches is to allow each channel to be switches separately AND use the two original bias pot holes for the switches. These holes are not used on the VTA version of the ST-70. There are some audiophiles that use TWO ST-70's and vertically biamp with the woofers in ultralinear and the tweeters in triode - and as such, there is an advantage to have separate switches for each channel. Yes - I know there is less output in triode but a number of audiophiles have told me that they like the way their system sounds like with the woofers in ultralinear and the tweeters in triode.

    Re: >"I do not however believe in throwing the switch on the fly because any switch you use in that location is NOT rated for the voltage it sees so my recommendation as well as others on other forums is to not throw the switch on the fly for safety sake."

    There is negligible voltage difference from ultralinear mode to triode mode on Dynaco amps and, as such, there is no harm to switching the amp while the amp is running as long as you don't do it at higher volume levels. You should turn the volume all the way down when making the switch. With the switches used on the VTA kits all you hear is a tiny "blip" when the switch is made. There is no harmful voltage spike when the switch is made because the voltage gradient is very low.

    Bob

    burnedfingers

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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by burnedfingers on Sat Jan 07, 2012 2:09 pm

    Finally someone agrees with me. Wink Had one fry the switch and I only had about three uses on it. Made a very loud pop for me. Only took a few times for me. After that I waited for the power supply to go down before bringing it back on line.

    tubes4hifi
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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by tubes4hifi on Sat Jan 07, 2012 3:39 pm

    I'm not so concerned with the switch itself, a good quality switch doesn't have to have a high voltage or high current rating here (use a toggle, not a rotary)(the voltage difference across the switch is less than 10v),
    my concern is that during that millisecond of switching, that little glitch or pop could take out $100+ worth of tubes (or worse, your speakers). For that I can wait a minute or two to shut the amp down, let it cool off slightly (don't want to pop the HV rectifier when you turn it back on hot) make the switch, then power up.
    It's been said a thousand times, you'll have more bass and treble (and more power) in ultra-linear,
    but you'll have a better midrange in triode. The difference is very similar to the difference between
    the sound of KT88s and EL34s.

    Guest
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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by Guest on Sat Jan 07, 2012 4:24 pm

    My sense is that the triode has a better balance top to bottom. This would make sense if UL tends to push the bottom and top out. The reduction in power is hardly noticeable, but I don't play music at ear splitting volumes anyway. I must admit that when I put on Jimi or Led Zep, that I had some very large ear bleed speakers, and the amps to go with them

    Guest
    Guest

    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by Guest on Sat Jan 07, 2012 8:46 pm

    Ideally, if you had an audio version of heavy duty jumpers, similar to non-fused HVAC service disconnects, you could do it that way. It still would not be advisable to change modes it with the amps on, but you would not have to worry about voltage passing through the thing.

    Ask far as the sound of anything who can say what's right. A friend of mine bought a bunch of Mark Levinson gear (ML-2s ML-7, plus a pair of Quad 63s) from a guy named Peter McGrath. Michael said that McGrath always said that with any gear, it was a case of choose the distortion you like best. It's the old: Ford or Chevy, Martin or Gibson, etc. I honestly feel that the pursuit of audio perfection can be a very long road with no end. I like to sit and listen every once in a while, so I don't what to let tweaking become an end in itself. I can't remember exactly who, but I think it was Picasso that said that, paintings are never finished, they are merely abandoned.

    Bigron865

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    Join date : 2013-03-15
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    Location : Birmingham Alabama

    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by Bigron865 on Thu Apr 04, 2013 8:13 pm

    Bob I know this post is kind of old but its new to me. Does all of this still pertain to the newest low gain or classic vta mods that I just did? I'd love a sweeter sound. I have the PIO caps and an upgraded quad cap on order. Should I leave it in pentode till I break those in and then try the triode mode?

    Ron

    Bob Latino
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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by Bob Latino on Thu Apr 04, 2013 8:19 pm

    Hi Ron,

    Yes - The triode mode also applys to the lower gain CCS VTA driver board. In triode mode you only have about 60% of the power of ultralinear but the amp but the amp spunds a little "smoother" with more mid range projection. This is nice for vocals and acoustic jazz.

    I don't think it makes any difference which mode of operation you use to break the amp in ...

    Bob

    Bigron865

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    Age : 48
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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by Bigron865 on Fri Apr 12, 2013 3:44 pm

    Bob I bought 2 switches today from a local electronics supplier. They look like the blue ones in your pictures but these are red. The rating was 10a 250v ac. Will these work for triode/pentode switches?

    cheehpogi

    Posts : 4
    Join date : 2015-03-05

    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by cheehpogi on Tue Mar 10, 2015 10:25 pm

    Hello from KY, my first post here and I would need some help. I did the resistor mod on a newly acquired st 70,well before the mod for me I think the amp sounded great but after the mod and adjusting the bias it seem flat so I revert it back to the original pentode mode and bias was still at 1.30 but to me it still sounded flat, is there anything that I did wrong? maybe I biased it wrong. What I did was the black probe on ground and the red probe I stuck it to where it would read 1.5++ and then adjusted the bias screw until the numbers went down to 1.30. Did I miss or messed up something? Newb here need some guidance. Thanks.

    peterh

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    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by peterh on Wed Mar 11, 2015 2:39 am

    If it is a "dynaco" the bias should be 1.5V

    cheehpogi

    Posts : 4
    Join date : 2015-03-05

    Re: Run your Dynaco ST-70, Mark II, Mark III or Mark IV in TRIODE MODE - photo

    Post by cheehpogi on Wed Mar 11, 2015 9:59 am

    peterh wrote:If it is a "dynaco" the bias should be 1.5V  
    Reading on Bob's previous post, he stated that stock dynaco tubes should run at around 1.25 since we are not using the original mallard tube.

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