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VHT Special 6 Tube Substitution

Discussion in 'Glowing Bottle Tube Amp Forum' started by pete-strych, Dec 7, 2015.

  1. pete-strych

    pete-strych Tele-Holic

    951
    Jun 19, 2012
    I have an upcoming writing & recording project beginning in the new year with a small budget. We are in need of a single-ended 6L6 tube boutique amp to be used during these sessions with a bunch of high end pedals.
    Just ran across VHT Special 6 & Special 6 Ultra heads. Does anyone use these? Can you drop a 6L6 output tube in place of the 6V6? Does it have a bias pot?
    I know VHT encourages DIY'ers to mod this sucker....that is pretty cool.
    I'd love to here from owners.
     
    yardleyboy likes this.

  2. radiocaster

    radiocaster Friend of Leo's

    Aug 18, 2015
    europe
    It could be done I'm sure, but besides the simple electronic modding you would probably need to change the output transformer.

    Maybe you should get a Ramparte instead...
     

  3. theruns

    theruns TDPRI Member

    31
    Dec 31, 2011
    Minnesota
    You can just pop it in and go from what I've heard. I own one but haven't bought a 6l6 to try in it yet. I know if you search for the vht special 6 mod thread there are a few people who have done it and from what I recall you don't really need to make any major changes to the circuitry.
     

  4. pete-strych

    pete-strych Tele-Holic

    951
    Jun 19, 2012
    That's totally what I thought, that I can just drop a 6L6 or Big Bottle KT66 in there. I've done that in the past with Champ Clones that I built. I I am NOT a fan of 6V6 tubes at all, & I'm just not familiar with VHT amps these days. For the price, this little amp head may serve us well as a blank canvas for some pedals while recording.
     

  5. theruns

    theruns TDPRI Member

    31
    Dec 31, 2011
    Minnesota
    They are awesome little amps for recording IMO. I love mine but I think I need to start trying different tubes :idea:
     

  6. pete-strych

    pete-strych Tele-Holic

    951
    Jun 19, 2012
    Those amps seem like they'd be useful & inexpensive tools for recording. It's common, though, that many amps are shipped with cheap Chinese, or other lame sounding tubes. But that's such an easy fix to retube with some quality valves. I really think I might pick one up for this session.
     

  7. theruns

    theruns TDPRI Member

    31
    Dec 31, 2011
    Minnesota
    Yeah the tubes that came with it were pretty brittle sounding to me. I have JJs (6v6 and 12ax7) in it right now that sound awesome. but i definitely think a 6l6 is in my future!
     

  8. CAAD8N8

    CAAD8N8 Tele-Holic

    632
    Nov 21, 2010
    Ohio
    I had a 12/20 that could run on el84/6v6 and el34/6l6 tubes. You just had to flip a switch and the bias was squared away. Not sure about the smaller versions though
     

  9. powerwagonjohn

    powerwagonjohn Tele-Meister

    182
    Apr 30, 2013
    minnesota
    Yea , you can swap all these tubes with no problem. I have had mine for 4 years or more and have replaced all the tubes several times with vintage tubes. It is a fun little amp. I have the combo and thought I would have to swap the speaker out but never did. I am running an old coke bottle 6V6 and some old pre amp tubes. The only time I had a problem was with a KT88 and the amp started cutting out.
     

  10. TNO

    TNO Friend of Leo's

    Apr 25, 2003
    NC-USA
    If you just swap the larger tubes in without changing the cathode bias resistor it will be biased very cold. Check the mod thread for an easy fix. If you don't want to mod the amp the 6V6 will probably sound the best. The Tung Sol 6v6 reissue is a good one.
     

  11. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    The Special 6 and Special 6 Ultra are cool little amps and a great value. They are cathode biased so they don't come with a bias adjustment pot.

    The output transformer impedance match can be optimized by using a lower impedance speaker than with a 6V6. For example, if the amp wants an 8 ohm speaker with the 6V6 you can run a 6L6 with a 4 ohm speaker to optimize the output impedance match.
     
    DaveKS likes this.

  12. pete-strych

    pete-strych Tele-Holic

    951
    Jun 19, 2012
    I'm gonna be on the lookout for sales after Christmas. I think I'll be picking up a Special 6 Ultra head for the studio. I'm totally digging this thing.
     

  13. Impellitteri

    Impellitteri TDPRI Member

    29
    Apr 2, 2016
    Philippines
    I tried this one. It made a huge difference. It sounded bigger as compared to the stock 10in VHT speaker. Would it be ok if I don't change the cathode bias resistor with this setup?
     

  14. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States

  15. Impellitteri

    Impellitteri TDPRI Member

    29
    Apr 2, 2016
    Philippines
    Thanks Rob. I've been studying for quite some time your upgrades. It's really a great help including Master Kleuck's inputs as well. In my case, I won't be needing the switch because I will be permanently using my 5881 and the likes. I need the additional power but without the gain. My question now is what resistor should I use in parallel; 680ohm/5w or 560ohms/5w? This will result to 278ohms and 256ohms respectively.
     

  16. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    256 ohms is what you want.
     

  17. cabra velha

    cabra velha Tele-Holic Platinum Supporter

    780
    Jan 21, 2016
    sub arctic
    So reviving this a little.

    Since I run my S6U full throttle all the time when playing the Tele through it, I've decided I want a little more oompf. To this end I would like to move to the EL34 option and would just as soon leave it in full time (so no switching needed).

    So the question for Rob would be: Can I just swap the existing 470ohm R39 with a 250ohm 5w or is that going to be too hot for an EL34? I'm running a cabinet from the S6U head and my 12" WGS is 8ohm so the speaker impedance trick is doable.
     

  18. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Yes, replace the power tube cathode resistor with a 250 ohm 5 watt resistor. A 10 watt resistor would be a good upgrade though.
     
    cabra velha likes this.

  19. Clarkj734

    Clarkj734 Tele-Meister

    208
    Nov 24, 2015
    Bloomfield Hills, MI
    Another question for Rob... if you don't mind.

    So far I have only been swapping between 6v6 and el84 via the adapter in my S6U head. Right now I'm running a stock VHT Chromeback in the 1x12 VHT cab. Surprisingly, I quite like the speaker and don't feel the "need" to upgrade it necessarily. It's a 16 ohm speaker...

    So, if I chose to run a 6L6 or 5881, can I still use the Chromeback ? Being that it's 16 ohm, will this be an issue?

    I thought I read where VHT suggested that you could run a 6L6 / el34, etc. with the 16 ohm Chromeback - with the head set to 8 ohm speaker impedance. I didn't exactly understand that, but it seemed to say that by doing this you didn't necessarily "need" to adjust the bias resistance...


    Am I misinterpreting this? Would I be better off going to an 8ohm speaker?
     

  20. Gatordad

    Gatordad TDPRI Member

    Age:
    62
    74
    Sep 18, 2003
    1,000 miles from nowhere
    I have the VHT Special 6 Head and have tried 5881 and 6L6 tubes. Here is a portion of an email I received from VHT customer support when I asked about settings when I swapped power tube:

    "when trying a 6L6 (or other larger tubes like EL34, etc.), it's best to use the amp's speaker jack that is twice the actual speaker impedance. So plug your 8-ohm speaker into the amp's 16-ohm output jack."

    I've been using a NOS Jan Sylvania 6L6GC with my 8 ohm cab plugged into the 16 ohm jack as suggested. No mods required. I also use a JAN GE 5751 preamp tube.

    Hope this helps.
     

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