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    Hello from new Mark VI owner

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    ricohman

    Posts : 11
    Join date : 2012-12-24

    Hello from new Mark VI owner

    Post by ricohman on Mon Dec 24, 2012 1:14 pm

    I just discovered this forum last night and I thought I would say hello as I am presently recapping and rebuilding a pair of Dynaco Mark VI monoblocks.
    Here are a few pics.






    One of my amps has a bad tube and the alternate Japanese transformers. It is nearly 5lb heavier than its "little" brother.


    I have ordered new caps, resistors and the dual section cans. I also bought two sets of matched 8417's.




    I'm not a tube amp guru but I have learned a lot. These are my first tube amps and they will be powering a set of Altec 19's. I don't know what the future holds for these amps as they are fairly rare and the supply of the expensive 8417's is dwindling.
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    Bob Latino
    Admin

    Posts : 2527
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Hello from new Mark VI owner

    Post by Bob Latino on Mon Dec 24, 2012 2:49 pm

    Hi - and welcome to the Dynaco Tube Audio Forum. Yes - not too many of the Mark VI's were made. The amp (unless modified) can only use the 8417 output tubes. You may want to investigate the changes that would be necessary to convert them to use 6550 or KT88 output tubes. Triode Electronics has some info on how to do this here > Convert an amp from 8417 output tubes to use 6550 output tubes

    Bob
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    Sal

    Posts : 221
    Join date : 2009-02-05
    Location : Central New Jersey Dynaco-ST70.com

    Re: Hello from new Mark VI owner

    Post by Sal on Mon Dec 24, 2012 3:52 pm

    Welcome to the forum. I also have a pair of Mark VI's, but I have not connected to them speakers yet. Yours pair are in very nice condition. Hopefully your 8417's test good as they are hard to find NOS. I managed to snag a couple of NOS quads as my amps did not come with tubes. Well 1 amp had 6550's in them.

    Sal

    ricohman

    Posts : 11
    Join date : 2012-12-24

    Re: Hello from new Mark VI owner

    Post by ricohman on Wed Dec 26, 2012 12:04 pm

    Thanks for the welcome.
    I hope to learn more about these amps and tube amps in general. I am going to run these in the factory configuration when they are recapped.
    I have read some about using different tubes but that is way out of my knowledge base and I would have to ship them somewhere. And when you live in rural Saskatchewan somewhere is a long way and these amps are 55lbs each.
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    AntiWendel

    Posts : 3
    Join date : 2017-03-16
    Age : 53
    Location : Stockholm, Sweden

    Re: Hello from new Mark VI owner

    Post by AntiWendel on Thu Mar 16, 2017 9:29 am

    Hello
    Old thread, but I am also a new mk 6 owner, using the Kt88 tubes w individual bias.
    I was informed by a swedish tube "guru" that the replacement of the original 8417 tubes results in worse performance and sound, due to the transformer/tube mismatch.
    Anyone with any experience of this ?
    Thx
    A
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    j beede

    Posts : 388
    Join date : 2011-02-07
    Location : California

    Re: Hello from new Mark VI owner

    Post by j beede on Thu Mar 16, 2017 12:41 pm

    Simply replacing 8417 with KT-88 without compensating for the lower transconductance of the EL-34/6550/KT-88 should reduce the power output of the MKVI. Given the available surplus of output from the MKVI this may or may be noticeable to you.

    As I recall the MKVI runs with a B+ spec'ed at ~500V. Just a bit higher than the MKIII. If your ac mains run high at your location I suppose you might be pushing a 6550 closer to its plate voltage limit. EL-34 and KT-88 are spec'ed higher. NOTE: It is not unusual for people to claim that modern tubes do not meet their plate voltage max spec. I have not experienced this myself. My VTL 80 had a B+ of 650V and I had no EL-34 failures nor did I expect any. FYI: I bumped into Luke Manley a while back and asked him about high B+ in VTL amps--he was surprised that I thought 650V was high.

    The topology of MKVI is similar to other Dynaco amplifiers. Dynaco used 7199/6AN8 to drive EL-34, 6550, KT-88, and 8417. I would expect the negative feedback ratio to be reduced in the MKVI given the lower output at the 16 Ohm tap for a given 7199 operating point when replacing the 8417 with EL-34/6550/KT-88.

    Bottom line: If the MKVI really does sound "worse" with KT-88 I would look at the circuits before the KT-88s before blaming tube/transformer matching.
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    AntiWendel

    Posts : 3
    Join date : 2017-03-16
    Age : 53
    Location : Stockholm, Sweden

    Re: Hello from new Mark VI owner

    Post by AntiWendel on Thu Mar 16, 2017 1:06 pm

    j beede thanks for your insightful response- I have the feeling I will spend a lot of time w my mk6 and on this board...
    Very nice indeed Smile
    Have a good day in california !
    Regards
    Anti
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    peterh

    Posts : 799
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Hello from new Mark VI owner

    Post by peterh on Thu Mar 16, 2017 6:42 pm

    I cannot see any reason that KT88 will give any problems in MK6 , providing it is
    a tightly matched quad. One might loose sensitivity as the Gm is less ( the KT88 will need
    more g1 swing to get the same power), but with this type of amp i do not expect
    a real listening setup to notice.

    But, a tight match is needed !
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    AntiWendel

    Posts : 3
    Join date : 2017-03-16
    Age : 53
    Location : Stockholm, Sweden

    Re: Hello from new Mark VI owner

    Post by AntiWendel on Fri Mar 17, 2017 4:38 am

    This schematic came with my amps

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