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Thread: VHT Two/Ninety/Two - acceptable tube substitution ?

  1. #1
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    Default VHT Two/Ninety/Two - acceptable tube substitution ?

    Because of the high plate voltage of the VHT 2/90/2 running a typical 650 volts with the stock Sovtek KT88's,
    can one "safely run" matched GE 6550's ?

    My amp was built in 98'

    I found the tube data sheets for the GE 6550 here:
    www.drtube.com/tubedata/htm

    showing design maximum values of 660 volts in pentode mode/duet.

    I don't want to risk a quad of these GE 6550 costing $450+ on this experiment, but was hoping these might sound good in this 2/90/2 if there was no risk involved at these voltages.

    Thanks

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    anybody ?

  3. #3

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    There has been some tube-related controversy on the forum lately so I doubt anyone is going to give you any advice to be honest.

    If I were you I'd try to find someone who knows this particular tube inside and out and can tell if they are tough enough to handle voltages near the top-end of their range.

    Good luck !

    Giga

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    There is no risk using 6550s. Any power tube listed in the 6550/KT88 range of operation, including KT90 and KT120 can be used in the 2/90/2.

    Some variations of these might exhibit higher or lower transconductance which may cause difficulties when biasing. So if the tube cannot be biased properly - meaning that the overall bias range is either too cold or too hot for a particular set of tubes, you'll need to try another set (recommended) or modify the bias control range (not recommended unless you really know what you're doing).
    Dave Phelge
    Chief Misconception Eradicator
    support@fryette.com

    "We are what we pretend to be, so we must be careful what we pretend to be". - Kurt Vonnegut

  5. #5
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    On a side note, is biasing required when changing tubes with the same Sovtek KT88s?

    Thanks!

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    Biasing WHENEVER you replace power tubes is ALWAYS recommended.
    Dave Phelge
    Chief Misconception Eradicator
    support@fryette.com

    "We are what we pretend to be, so we must be careful what we pretend to be". - Kurt Vonnegut

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    I have a Fryette model Two/Ninety/Two and I am looking for a possible mod for 6L6s ...

    Due to circumstances I had to let go of my first Soldano X88R > Lexicon/Ecllipse > VHT 292 > (1x12 or 2x12) EVM 12L that I used almost exclusively for over 10 years ... Catching a bit of the Dumble “virus” I ended up getting the 6L6 based Bruno Super 100 which although is extraordinary in detail in a high gain mode, I find I am not a fan of the low-mid/chirp/chewy thing for lots of the stuff I used the other rig for ...

    So, I found a replacement X88R and just got it back from Soldano last week — Bill, re-capped it, replaced some pots under warranty, put in the WH mod on the third channel and blackfaces the first ... beautiful job.

    I plugged it into the of the Bruno Super 100 power amp insert, since I had not found a 292 yet, and was blown away by how beautiful it was — it was like have an old favorite lover return only better, excited, I ordered a new 292.

    But when I hooked up the X88R — I found, even though, many things that I loved about that combination were there, I like the 6L6s better for the cleans and the 3rd channel — I confirmed the conclusion by playing the X88R though the power section of a Fender Concert (II) w/ 6L6’s — so I guess, I like the arrangement better and further surmise that, like the SLO, this pre, like 6L6/7851A’s and are a great match (for me).

    In some cases, the its not the tubes but the circuitry that defines the tone that one likes — I wonder if there is a tweak or mod, in either case, that you can offer?
    Last edited by merkaba22; 06-23-2013 at 04:20 PM.

  8. #8
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    Hmmm. I just saw this, and your explanation here is much more clear than your post on TGP.

    First of all, no, you cannot run 6L6s in the 2/90/2.
    BUT - you can get a 2/50/2 built on a custom order basis with specially designed 6L6 optimized output transformers.

    Contact support@fryette.com for details.
    Dave Phelge
    Chief Misconception Eradicator
    support@fryette.com

    "We are what we pretend to be, so we must be careful what we pretend to be". - Kurt Vonnegut

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