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Tube recommendations for Demeter VTBP201?

Discussion in 'Amps and Cabs [BG]' started by paulraphael, Apr 13, 2006.


  1. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    Between tunes I'm hearing cryptic messages emanating from my amp ... it seems to be the voices of truckers zooming by on the Brooklyn-Queens Expressway. Time for some new tubes.

    So far I've used the original chinese tubes that came with the preamp (crappy), some Sovtek WA tubes (a bit better), and then the current Sovtek LPS tubes (quite nice).

    In the last couple of years I've discovered how great some of the older NOS tubes sound in my stereo. But Jim Demeter warned me that microphonics can be a big issue in any preamp that has horizontal tubes ... a lot of tubes that are fine upright ring like crazy when they're on their sides. He was the one who recommended the LPS tubes to me a while ago (he hasn't answered my more recent email).

    Any thoughts? I'd like something warm and sweet, but not mushy. I also don't want anything too exotic. Not interested in paying a ton, or in falling in love with something I'll never be able to find again. What tubes have other Demeter users had success with?

    Thanks,
    Paul
     
  2. I've rolled quite a few tubes through my 1.5 space Dem 201. Here is the short list of my favorites (and not so favorite):

    1. JAN GE 7025 tubes - Really nice, round tone - can be found often enough on eBay or online tube vendors. Very solid tubes that seem to do well horizontally.

    2. JJ/Tesla ECC83 tubes - Great bass response and super gain. Don't confuse this with the new ECC 803 long plate (see below). Like the GE tubes, they are solid, short plate designs that do well horizontally.

    Did not like:

    1. Soviet 12AX7WA - too much noise for me - tried 4 of these. Solid tubes, but noisy.

    2. JJ ECC803 long plate - Just didn't do well in a bass preamp IMO. Much more of a guitar tube - broke up way too easily without enough headroom for the Dem.

    - On the microphonics note - have you tried using tube stabilizers? They are rubber rings that help dampen vibrations. I use them to nice effect on horizontally installed preamp tubes. Pretty inexpensive on eBay.

    Jay
     
  3. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    Thanks Jay, I'll keep an eye out for some of those.
     
  4. That has NOTHING to do with the tubes. That's a grounding/sheilding issue, either with your bass or your electrical wiring. All better tubes will do is allow you to hear it better.
     
  5. Thanks PBG - I actually meant to comment on that, and forgot to completely.

    "Allow you to hear it better" :p - I might have to use that quote in a signature in the not too distant future. That o.k. with you?

    Jay
     
  6. GT 12AX7M Mullard Copy
    Electro Harmonix
    Tung Sol Re-issue
    TAD
     
  7. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    Good NOS preamp tubes should last for decades, so why not get something really good? You may never have to change them.
     
  8. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    DFW, Texas
    Jan Philips 12AX7WA sound very smooth and balanced in my 201S
     
  9. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.

    Well, I've actually experienced this before in other amps. Some tubes become radio receivers, along with other symptoms of dying. My current tubes had already started making intermittent dying tube noises; the radio reception came a little later.

    My chinese tubes in my old tubeworks head started picking up a french radio station right before they became useleless. I knew someone who was an amp technician, who said he had an amp on his bench, and when he turned it on it started talking to him about jesus(!).
     
  10. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    I know they should, but it seems like they often don't. Or else it's hard to know which ones are good. In my stereo preamp I've had some very nice vintage NOS tubes that tested beatifully but that have died early deaths. And this is a preamp that just sits on a shelf ... it doesn't take the abuse of the bass amp. I also don't feel flush enough to be spending $70 or more on a pair of tubes. Even if I knew they'd last forever.

    I'll take a look for the Jan tubes you guys mentioned. The tube stabilizers sound like a good idea, too. I have a set in my stereo pre ... probably makes even more sense in the bass amp.
     
  11. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
  12. For an audio amplifier tube to become a demodulator (radio), it would have to experience a drastic change in its input impedance and parasitic oscillations, which would be a coupling capacitor problem, not one with the tube itself. If this condition continued long enough it would kill the tube, but the tube's death would be a symptom of the stage coupling problem, NOT the cause. Putting another tube in its place is a band-aid and all you're doing is killing another tube prematurely. Preamp tubes last the life of the amp under normal circumstances.
     
  13. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    i have no idea what's behind it. only that for me and a couple of others who have experienced this, replacing the tube was a permanent fix.
     
  14. You're right. You don't have any idea what's behind it and I explained to you what does. If you don't believe me, fine. Ask some HAM radio guys or anyone who's had any experience with television repair or engineered for TV or radio. This is BASIC stuff.

    Given that you talk about having to replace preamp tubes alot, there's nothing "permanent" about your "fix." If you want to waste money and kill otherwise nice tubes, that's your prerogative.
     
  15. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    "Given that you talk about having to replace preamp tubes alot, there's nothing "permanent" about your "fix.""

    Well, the only other time it happened to me was with a tube that came in a used amp. This time it's with tubes that I've been using for eight years in a different amp. But as H.L. Mencken used to say, "you could be right."
     
  16. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    Thanks Jay, I'll keep an eye out for those.
     
  17. teleharmonium

    teleharmonium

    Dec 2, 2003
    Unless the preamp tubes are in a combo box with the speakers, or sitting on top of the speaker cab, microphonics are not likely to be a problem.
    If they are, you can put mechanical dampers right on the tubes. I have some of those high temp silicon rings they sell on ebay in some guitar combos that are prone to that (EF86 tubes mostly). They work pretty well although they can't make it go away entirely if you have a lot of sound close to the tubes.
    I think the Teslas sound good for bass. But, I mostly use Mullards, or other tubes made at some Philips plant in the 60s or 70s. Those things go almost forever and they have a nice high end.
     
  18. ...which will do absolutely NOTHING. Microphony is a mechanical resonance of the internal elements. Damping the glass only makes the tube far less efficient at shedding heat. It does NOTHING to stop microphony.
     
  19. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    "Damping the glass only makes the tube far less efficient at shedding heat. It does NOTHING to stop microphony."

    I haven't tried them in a bass amp, but I've used them on stereo preamp tubes. With some NOS tubes I was using they made a noticeable difference. They reduced a lot of upper midrange/low trebble glare. But it's hard to imagine they'd be any match for the kind of shaking my rack gets when it's sitting on a bass speaker.
     

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