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SWR Preamp Tube Experiment Results

Discussion in 'Amps and Cabs [BG]' started by skinnypete, Mar 22, 2005.

  1. skinnypete


    Oct 7, 2004
    New York, NY
    Disclaimer: the results of this experiment are not extensive and not very scientific. Your results may vary.

    After reading a few threads regarding how the sound of SWR pro series amps can be altered by replacing the stock preamp tube, I decided to experiment with a couple of different brands.

    Anyone who has ever used SWR knows the stock sound and if you aren’t familiar just look around this forum. Suffice to say, we wouldn’t be spending the time and money changing our preamp tubes if we were in love with the stock SWR sound.

    The stock tube was a Ruby tube 12AX7-CZ Selected. That number is not listed on the Ruby tube website but the closet thing is a Chinese tube which leads me to believe that the stock tube was Chinese. I mention this only because the majority of tube users I have spoken with consider tubes from former Soviet block countries and the toxic old days of big industry USA to be far superior.

    I chose:
    Electro-Harmonix EH-12AX7 (Russia) $9
    JJ Electronics 12AX7 (Slovakia) $8

    These were purchased from revolutionguitar.com

    I was only expecting subtle differences and for the most part I was correct. The differences are slight but noticeable, nonetheless.

    I found the JJ tube to be warmer and woody, a little fuller than the stock tube.

    The EH tube had a more aggressive, mid-range sound and also little fuller than the stock tube.

    I used a Fender Jazz with stock pickups and Rotosound roundwounds. I played the SWR through a single 18" cab (Sonic) and separately through a stack consisting of 1 Avatar 2x12 and 1 Madison 1x15 (the tweeters were turned off)

    This is still a very hi-fi and transparent amp with no real bottom end but that is another story.

    My thanks to the member who suggested changing the preamp tube and also the member who suggested revolutionguitar.com.

    Maybe I will try a high end Ruby tube or another brand and keep you all updated. Or, maybe I will just get a new amp
  2. Bongolation


    Nov 9, 2001
    No Bogus Endorsements
    It's going to take a lot more than a preamp tube to change the SWR sound. If you don't like the sound of SWR gear, why did you buy it? That's the part that I never understand in these discussions.
    It is.
    Old western European tubes like the Mullard or the Dutch Amperex are better than anything available today, but the difference in quality between Chinese and former Warsaw-Pact countries' current production tubes are not as clear-cut. The latter need extensive culling (up to 40% or more, according to Lord Valve) of defective raw stock.
    They're slight enough that I no longer bother to change preamp tubes in stock amps (especially bass amps) unless there's an actual problem, such as idle noise, which is often cleared up by tube substitution. Changing to a different preamp tube is not going to make a silk purse out of a sow's ear.
  3. protoz


    Nov 30, 2000
    I recently tried this with my Hartke changing the GrooveTube 12AX7 out for a EHX 12AX7 (Russian) and I get quite a bit more punch.

    I think the GT was pretty worn out though it was around 5 years old with steady playing.
  4. Finger Blister

    Finger Blister

    Jul 8, 2003
    Thanks for the review!

    Proper Preamp tube is important is SWR front-ends.

    They do make a difference.

    The stock SWR for used for many years were 12AX7-C / C-9, AKA 12AX7A/7025 labeled Groove Tubes, Ruby, Mesa, whatever...
    is recognizable by the vertical strut: chin.

    These give the characteristic harsh highs, or sterile tone that many critics attribute to SWR.

    The tone can find warmth, depth, sweetness and a different character with the correct tube...
    ...especially when use the SWR DI out (oohwee!).

    Ken's SWR Preamp Tube Review
  5. Bongolation


    Nov 9, 2001
    No Bogus Endorsements
    This is not the tube that currently comes in SWRs.
  6. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    Endorsing Artist: Black Diamond & SuperSensitive strings
    I've been happiest with a JJ/Tesla ECC83 in my SM-400 and SM-400S. I tried several tubes through each and liked that tube's balance of tone and punch the best.
  7. I have tried the following tubes:

    GT 12AX7R : ok, but nothing to right home about

    EH 12AX7: Decent but not as good as the Groove Tubes

    12AX7M Mullard copy which had good-distinct low end and mids, ok highs.

    NOS GE 5751 (Military version similar to 12AX7): Good sounding, slightly less gain than 12AX7

    The absolute best tube in my experience is the NOS 12AX7 RCA Blackplate. There is no comparison of the others with this one. Low end better than 12AX7M. Mids excellent, Very smooth but detailed highend. Louder and cleaner than the others. Well worth the $45 I spent.