Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Worthwhile retubing single tube Vox?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Michael A., Jan 6, 2016.

  1. Michael A.

    Michael A. Tele-Holic Silver Supporter

    773
    Jan 12, 2013
    Virginia Beach, VA
    My main practice amp is a 1999 Vox Cambridge 15 hybrid with a single 12AX7 tube. I don't understand circuits at all, but have read that this tube does not work like a conventional pre-amp tube in this application. I don't know what that means for its tone, which I am currently happy with. But I read so much about using NOS American tubes, that I was curious if I should grab a 12AX7 variant when I see them up for sale on CL. Would it make an audible difference?

    If anyone else uses this amp and has a strong recommendation, please let me . I guess some direction in terms of whether to look at tubes with more gain or less would be helpful too.

    Thanks.
     

  2. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    That tube is probably a 'warming' tube....there to keep the amp from being as harsh and brittle as it might be without the tube. I could be wrong. At any rate, the only way to see what changes with different tubes would be to try different tubes.
    Fwiw, IMHO, one tube does not a hybrid amp make.
     

  3. Johnny Cache

    Johnny Cache Former Member

    Mar 6, 2014
    Oregon
    I'm not too familiar with that Vox amp, never worked on one. I think you have to figure out what the tube does. If it's like allot of the amps built back then, for example Marshall valvestate's of about that year all it does is boost the overdrive channel for some distortion. My Brother-In-Law had a Marshall 8080 and the lead channel sounded like crap. I replaced the 12AX7 and it still sounded like crap. We came to the conclusion the tube only worked on the overdrive. Did nothing for the normal channel. I gave him a Blues Jr. I repaired, but didn't like much, he sold the Marshall, he's been happy ever since.

    You might try pulling the tube and see if the amp works without it.
     

  4. JD0x0

    JD0x0 Friend of Leo's

    Age:
    27
    Feb 22, 2009
    New York
    It's probably the same thing as they do in the Vox VT's.

    There's a preamp tube between the Preamp and power stage. AFAIK it doesn't do much until you crank the master up, where it will likely drive into clipping. On my VT40+ it appears to sacrifice headroom, but it does get a pretty decent overdrive when the master volume is cranked. My guess is it's there to emulate some sort of 'Power section' breakup.

    I changed the one in my VT and it made an audible difference.
     

  5. Mike Eskimo

    Mike Eskimo Doctor of Teleocity

    Nov 9, 2008
    Detroit
    Oh you mean the Vox's with the night lites ?

    Those should be good forever or for however long you own your amp.

    (I do like a couple of those VT series amps to be honest)
     

  6. Abu Twangy

    Abu Twangy Friend of Leo's

    Mar 16, 2012
    Rocky Mount, NC
    Some years ago I swapped out the 12AX7 in a Vox Valvetronix amp. The stock no-name Chinese tube was swapped for one of my vintage Telefunkens.

    There was minimal improvement.

    The tube is used in a low voltage "starved" mode. Its presence does affect tone some but not enough to make swapping brands or even other tubes from the same family worthwhile.
     

  7. mRtINY

    mRtINY Tele-Afflicted

    May 7, 2015
    Orygun
    [​IMG]

    http://www.legendarytones.com/vox-valvetronix-ad120vtx-amplifier-vox-tonelab/

    It's more than just a "warming tube". It's an actual tube amp with different configurations available through switching and digital attenuation. There's an output transformer and a current driver to scale it up.

    If the digital effects were better, the VT amps would be awesome. They're good anyway.


    -tINY
     

  8. Cheshiergrin

    Cheshiergrin Tele-Meister

    288
    Oct 22, 2013
    Estacada
    I have one of those cambridge amps and I replaced the tube to see if it would smooth out the harsh overdrive produced by the amp. It did help, but I do not see getting too wild about nos tubes doing too much.
    The biggest improvement fpr that amp I found was plugging into a cabinet with a webber 12a125.
     

  9. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Whatever that one noval tube does, that amp is not a tube amp.
     

  10. surfoverb

    surfoverb Doctor of Teleocity

    Jul 17, 2007
    Virginia
    either way an NOS USA/British tube will last longer
    cant hurt to try. My guess is you wont be able to tell
    or it will be night and day.
     

  11. surfoverb

    surfoverb Doctor of Teleocity

    Jul 17, 2007
    Virginia
    correct. Its British so its a valve amp :D
     

  12. JD0x0

    JD0x0 Friend of Leo's

    Age:
    27
    Feb 22, 2009
    New York
    I could tell a difference between the stock Chinese 12AX7 and a new production tung sol in my VT40+, FWIW. Amp got brighter and chimier with the Tung Sol. Not sure if I prefer it, yet.
     

  13. Johnny Cache

    Johnny Cache Former Member

    Mar 6, 2014
    Oregon
    That's not a real schematic it's map for user info only. Doesn't explain the circuits or show the components. What kind of BS are they trying to sell?.
     

  14. Michael A.

    Michael A. Tele-Holic Silver Supporter

    773
    Jan 12, 2013
    Virginia Beach, VA
    Here's the actual amp. It is basically a ss Pathfinder, which came out about a year earlier, with the tube stage added. You have to remove the chassis to get to the tube, but it is really no big deal.

    I can't speak with any knowledge, but I suspect this amp is much simpler than the Valve Reactor or Valvetronix series.
     

    Attached Files:


  15. bparnell57

    bparnell57 Poster Extraordinaire

    Feb 10, 2014
    Philadelphia, PA

    It is how it functions. Upon replacing the tube in my VT20+ with a used old stock Mullard12AT7 (a better current driver) I noticed enhanced bass, more touch response, and more of a "tube amp tone", compared to the stock Chinese short plate 12AX7.

    100% of the amp's signal travels through the tube.

    I also noticed "high voltage" warnings on the PCB silk screening surrounding the tube socket, as well as a small transformer.

    The frame of the speaker also gets a reference lug attached to it for the feedback circuit.

    I put a Weber Chicago Series Ceramic 8" in the same amp, and now it's an amazing bedroom/recording amp. I mostly like tube amps because I can tweak them haha.
     

  16. john_cribbin

    john_cribbin Tele-Holic

    741
    Nov 26, 2014
    London
    I'd say go with your ears. If you like the tone stay with it. If you have issues then try a swop. But unless the current valve is poor quality / failing the 'improvement' may be minimal.
     

  17. mRtINY

    mRtINY Tele-Afflicted

    May 7, 2015
    Orygun
    They're selling a ~2w tube amp with a solid-state ICIS driver to boost the power (and allow scaling of the tube amp's output power).

    And, yes, that is a schematic diagram - just not one that shows every component. Call it a "block diagram" if you like. No, it's not the complete circuit.....

    If you're too much of a big iron snob to like it, don't buy it. We don't really care.


    -tINY
     

  18. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    tiny, I see what they are doing. The tube is more than just a warming tube. So, it is a hybrid amp....all solid state but for the power tube, imho.
     

  19. bparnell57

    bparnell57 Poster Extraordinaire

    Feb 10, 2014
    Philadelphia, PA
    Exactly, it is a true hybrid. I imagine that it would in theory be possible to disable the final current amplifier, and thus have a 1-2 watt hybrid modeling amp, but honestly I think it is a quite brilliant design.
     

  20. mRtINY

    mRtINY Tele-Afflicted

    May 7, 2015
    Orygun
    And, it's not like any other hybrid amp....

    To me, the two things that it has are probably the most important: Current-mode drive of the speaker and a output transformer. That it has continuous power scaling is a nice bonus.

    I think we have plenty of decent pre-amps that are modeled or SS these days. The sonic differences with triodes are rather subtle in competent designs.


    -tINY
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.