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6550 vs KT88

Discussion in 'Amps and Cabs [BG]' started by bassboysam, Jul 23, 2004.

  1. I have been trying to find out what exactly is the diffrence between these two tubes, power wise and sound wise, I am relatively new to the whole tube thing so please excuse my ignorance.
  2. KT88's can take higher plate voltage and dissipate more wattage, so they are more powerful (in the right circuit). But I have only used 6550's in my svt's. I had a Marshall Major with 6550's and it was only putting out about 60-80% of its power rating because it was designed for KT88's.
  3. You've come to the right place. Unfortunately, you're gonna get about twenty different opinions. In the end, the only way that will really matter is what you think after hearing both types in the same amp.
  4. MrBonex


    Jan 2, 2004
    New Hampshire
    I think KT88s are a little more "hi-fi." I'm not sure why. It might be the headroom.

    I love 'em both, but I prefer the KT88s. Both my amps have 'em and would never consider switching.

    That said, my drummer (!) has an original SVT with 6550s and I LOVE that amp! But let's face it, SVTs just simply rock.

    My Sound City Bass 150 does that Jack Bruce / Cream thing so damn well. So KT88s can rock pretty righteously as well. My band played "Smoke on the Water" for yuks a couple of nights ago and it totally nailed the tone. It was PERFECT!

    What the hell. Flip a coin.
  5. Thornton Davis

    Thornton Davis

    Dec 11, 1999
    Here is what The Tube Store in Hamilton says about the 6550WE and the KT88 power tubes.

    Sovtek 6550WE power tube.

    From our listening test:
    "Emphasis can be heard in the lower bass and highest highs. At times the response is a little sluggish because of its compression factor with a fast attack and slow release. When the tube is pushed, it hotspots in the upper midrange, which will really bring out the crunchy guitars in rock music."

    Now here is what they have to say about the Sovtek KT88 power tube.

    From our listening test:
    "Smooth, warm and clear with excellent imaging. The bass (except for the very bottom end) is tight and the high end is crystal clear. The separation of parts and balance is better than any of the 6550 types."

    These tube descriptions now include the results of the listening test we performed with Roman Klun, a recording engineer and producer who has worked with artists such as Sarah McLachlan and the Boomers. He listened to all our KT88 and 6550 types with his own reference recording and gave us his observations.

    You can read more on their site The Tube Store

    Good luck.

  6. A9X


    Dec 27, 2003
    Sinny, Oztraya
    Sonically, it depends on the circuit topology, biassing, output transformers, tube brand and vintage, power supply and a whole wealth of other details.

    As for power output, the datasheets say the KT88 has a higher plate dissipation and anode voltage than the 6550, but in reality, there would probably only be a dB or two in output difference (power) between two similar amps with the same number of output tubes and a similar design breif.
    Based on my experience of building a LOT of amps, anyone who says the 6550 sounds like this, or the KT88 sounds like that, are speaking out they're ass. They can have a particular sonic flavour in a given circuit, only.
  7. One of these days when I have some disposable cash I'll experiment with KT88's. I've heard they sound great in an SVT but I've also heard that 6550's are what give SVT's their signature sound. I needed to re-tube my SVT-CL (after 2 years of fairly steady gigging with the original tubes) and I just got a matched sextet of 6550's from Tubes and More for $111.00.
  8. My V9 (it's an SVT, trust me) has a set of Chinese KT88's in it and still sounds like an SVT. It's tube dealers trying to justify their prices of $50-100 per tube who "insist" that GE 6550A's are a requirement. They ARE tougher and made better than most current tube stock and I think that's the biggest difference overall. But with Sovtek making some excellent examples of 6550's and KT88's, the two versions of the KT90, and the new Chinese 6550A's and KT88's made on the same machines that made the original GE 6550A's, there are more choices for players today than even in the late 70's, in the amp's heyday, when you had GE or Sylvania.

    BTW, Rockit why did you feel the need to retube your SVT-CL?
  9. One of my tubes went microphonic and was picking up the vibrations of the spring retainers. I'd hit certain notes and it sounded like someone was dropping dishes.
  10. That's not power tube microphony. Power tubes will pulse or roar like a seashell, if you hear crackling, it's more likely a preamp tube. That said, if you have old Svetlana/now Flying C power tubes in there, they have a horrible problem with microphony as they age. Are you SURE it was the retainer you were hearing?
  11. So you can't really tell just by listening to an amp what type of power tubes are being used. I was just wondering because my YBA200 has 4 sovtek 6550we tubes and im guessing one day i will have to replace them.
  12. Yes and no. I can certainly tell the difference between output tube types just by listening, but I have a VERY refined ear. Guitarists I worked for who chased Eddie Van Halen's tone for years and tried all the BS mods and Variac crap were blown over when I get their Marshalls and get rid of the EL34's and drop a set of fat bottled 6CA7's in there, and BOOM, there it is. I also notice the difference between KT88's and 6550's in bass amps. KT88's are cleaner and more punchy where 6550A's get snarly when overdriven; that has to do with their respective peak current capability, a spec usually only published for transmitter tubes. In general, the "KT" series of tubes were made to be more rugged and handle more voltage than their cousins, so a few watts more of disappation and a couple hundred volts more max voltage can equal a LOT more peak current hitting the output transformer.

    There are lots of conflicting specs about high power beam tetrodes with at least six different rating curves for 6550A's alone that I have seen, and after working with thousands of them, I can tell you it almost always boils down to differences in each set themselves. There are general tonal qualities shared by a particular type, but some like higher voltage, some like higher bias, ect. The amp they're in IS the biggest factor, but like any active device, they will impart their own "sonic signature" to whatever they pass.

    Don't be so quick to try and kill off your Sovteks from old age. They ought to be good for at LEAST ten or fifteen years
  13. oh im sure they will be, but i know i would like to maybe try something diffrent after a few years, i could always get a set of kt88s and swap them out every year or 2 just to keep things fresh right?
  14. I don't see the point. That's a lot of bench work for no real reason. You'd need a rebias every time.
  15. Ive not used the 6550 tube in anything, my old 50 watter has EL34s as does the Hiwatt 100. I have however used the KT88 valve for twelve months now and must say its a very warm sound with plenty of headroom. I play Trace Elliot V4 and it (beleive it or not!!) has four. Ive never run out of headroom just using a single 4x10, Ive never gone for a "how loud is it on 10?" test as I fear for my speakers but it must be damn devastating...
  16. Yes, I tapped the chasis and the tubes and it was what I was hearing. I'm going to clean house and replace the preamp tubes as well. Might as well.

  17. supershifter2


    Apr 22, 2014
    This is a vintage antique thread BUT ! I gots to post I just ordered 6 of these with the cleanest no brake up grade available for one uh my 1971 blew line SVT's , AND 2 of those tubes for my 1959 Dynaco MK2 amp. Go from the preamp out on the Acoustic 220 into the Dynaco into a 15" Ciare woofer with a P bass with flat wounds.

    www.thetubestore.com - Genalex - Gold Lion KT88 Audio Tubes
  18. Wasnex


    Dec 25, 2011
    I am sure this tube will be great in the Dynaco. The reviews for the sound quality are very high.

    May not be the most reliable choice for the SVT due to the amp's high plate voltage. I have read many threads where people had problems running this tube in designs where plate voltage is close to 700V. This seems to be a common problem with many of the KT88 and 6550 types made by New Sensor. Several of the amps I have came with KT88EH or EH 6550. Lots of failures: Shorted tubes, low current, no current, drift in current match, won't hold bias at operating voltage (runaway). As these tubes have failed, I have replaced them with JJs.

    I have had good luck with JJ KT88s and run a lot of them with very few problems. Some other Talkbass members have had high failures with JJs, so IMHO it's good to buy from a vendor who does a good burn in before matching the tubes. The burn in helps eliminate bad tubes. The last set I bought came from Eurotubes. Current match between the quad was perfect and they have a 6 month warranty.

    With the SVT, you may need to replace the driver tubes. The amp uses the drivers to set the bias, and if the drivers are weak you will not be able to set the bias properly. This will depend somewhat upon upon the operating characteristics of the new output tubes.
    Last edited: May 16, 2018
  19. cerrem


    Apr 4, 2006
    San Diego
    I concur about the JJ KT88 tubes being reliable in the SVT's ....