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    Decware modification for EL34 amplifiers?

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    GP49

    Posts: 511
    Join date: 2009-04-30

    Decware modification for EL34 amplifiers?

    Post by GP49 on Thu Jan 13, 2011 12:33 pm

    A simple modification originated by High Fidelity Engineering Co., maker of the Decware tube amps (primarily single-ended triode) first showed up over a year ago.

    The claim is that it "virtually eliminates the universal problem all tubes have of stray electrons bouncing off the plate by manipulating (the suppressor) grids."

    It's been out there for over a year; also known as the Hazen modification, after the Decware technician who thought it up. I have not tried it but it appears simple and cheap enough, easy to implement and totally reversible on Dynaco amps with their chassis-mount (rather than PC board-mount) output tube sockets and using the EL34 tube (Mk II, Mk IV, ST-70). It consists of breaking the external connection between suppressor grid and cathode, and replacing it with a nonpolar 0.1uF capacitor. What I'm wondering: would be its applicability to a higher-powered push/pull Ultralinear amplifier be the same as to a low-powered triode amp?

    I may try it next time I have my Mk II amplifiers out for service, but in the meantime, has anyone else here attempted this modification?

    Announcement by Decware as a modification for THEIR amps:

    http://www.decware.com/newsite/paper145.htm

    Part Two: an attempt to explain the modification:

    http://www.decware.com/newsite/paper146.html

    The Decware forum, in which ONE member "Veryoldcat" reports trying it on his ST-70 with positive results:

    http://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1243915681/0

    mantha3

    Posts: 292
    Join date: 2010-11-10

    Re: Decware modification for EL34 amplifiers?

    Post by mantha3 on Thu Jan 13, 2011 1:24 pm

    Sounds interesting. I wish the tech. reasons for this sounding better was better known. I read these links you provided.

    So is this just running a .10uf 400+ volt cap between pins 1 and 8 on the EL34 tubes?

    I have a Bob Latino ST120 amp... running KT88 tubes. I think this would apply or perhaps benefit me as well as these 88s "have the same suppressor grid kept at the same negative DC voltage as the cathode" as the 34s..

    I'm to new to run this without some trial and error from others in here.

    I think I just break the connect from pins 1 and 8 and then run a .10uf 400+ volt cap. If you do it on an ST70 please report back.

    Tube Nube

    Posts: 330
    Join date: 2008-12-06
    Age: 51
    Location: Calgary, AB

    Re: Decware modification for EL34 amplifiers?

    Post by Tube Nube on Thu Jan 13, 2011 5:53 pm

    Should this mod deserve their attention, I'll be most interested to hear what some of our local guru members have to say about it for our amplifiers and the tubes we like to use in them, like the KT 66 or KT 88 types, for instance.

    GP49

    Posts: 511
    Join date: 2009-04-30

    Re: Decware modification for EL34 amplifiers?

    Post by GP49 on Thu Jan 13, 2011 6:06 pm

    Tube Nube wrote:Should this mod deserve their attention, I'll be most interested to hear what some of our local guru members have to say about it for our amplifiers and the tubes we like to use in them, like the KT 66 or KT 88 types, for instance.

    With some tubes, this circuit won't work; if the suppressor grid is internally connected to the cathode, for instance. So it cannot be used on the 6550, KT66 or KT88. This does not stop anyone from using an EL34 instead, should one want to try it but the EL34 has its own characteristic sound to begin with.

    Tube Nube

    Posts: 330
    Join date: 2008-12-06
    Age: 51
    Location: Calgary, AB

    Re: Decware modification for EL34 amplifiers?

    Post by Tube Nube on Thu Jan 13, 2011 11:00 pm

    Thanks GP,

    Since I've just ordered a set of gold lion repro kt 88s, I think I can stop worrying about this mod for myself, but I ll be interested in anyone trying it with "34's".

    mantha3

    Posts: 292
    Join date: 2010-11-10

    Re: Decware modification for EL34 amplifiers?

    Post by mantha3 on Fri Jan 14, 2011 2:14 pm

    Cool

    I have an ST120 (Kt-88 tubes). It sounds great. If I could do this mod I'd be tempted just to hear if any improvement is noticed. I'm happy but the curiosity of this thing sounding better may have been enough to act.. No need to worry.

    GP49

    Posts: 511
    Join date: 2009-04-30

    Re: Decware modification for EL34 amplifiers?

    Post by GP49 on Mon Jan 17, 2011 7:24 pm

    On a discussion of the Decware (Hazen) modification on another board, a user tried it on a fixed-bias amplifier (most of our Dynacos are fixed-bias) and got no sound at all. Checking with Decware, he was told that the modification only works with cathode bias amplifiers, not fixed-bias as are the Dynacos.

    Fortunately I had gotten lazy and decided to listen to music instead of modifying my amplifiers...

      Current date/time is Thu Dec 18, 2014 7:01 pm