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Are 6550's and KT88's a Direct Swap in an SVT Head?

Discussion in 'Amps and Cabs [BG]' started by StormeeBee, Jan 8, 2012.

  1. StormeeBee


    Oct 31, 2011
    Vancouver, BC
    Hey Guys and Girls,

    Is an Ampeg SVT-CL user able to swap their 6550 Tubes for KT88's directly? Is there anything the user needs to do other than adjusting the biasing screws?

    Also, what are the tonal differences between the two.

    Any help would be amazing!
  2. Yes you can, the KT88's give more headroom before distortion and a slightly sweeter sound (clean). The over-driven sound can be a little harsher though IME.
  3. svtb15


    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    what would the bias voltage be on KT88s if the spec on the 6550s is .071 on the test points? Or does it stay the same
  4. majortoby


    Jul 2, 2009
    Tampa, Fl USA
    I've heard rumors that Hendrix used KT-88's in some of his Marshall amps because he preferred the breakup characteristics. Any care to confirm or deny?
  5. Negative bias can be higher for KT88's. I use the distortion notch method, not a set voltage reading as valve requirements vary from run to run or even in the same production run.
  6. I believe that was KT77's not KT88's.
  7. StormeeBee


    Oct 31, 2011
    Vancouver, BC
    Thanks guys! I'm still mulling it over... Maybe some opinions with the following:

    1. If I like brighter highs, warm mids and tight lows... 6550's or KT88's
    2. What brand of either (reasonably priced, please):)
    3. If 6550's are the Winged C's really worth it?
    4. Are the JJ 6550's any good?

    Sorry guys... I'm a tone nerd with a nervous trigger finger.

  8. 1) Nudge to KT88
    2) Gold Lion (not most reasonable but there you go) for KT88, second Winged "C" 6550.
    3) YES Narrows the gap between 6550 and KT88s
    4) They are decent tubes not as good as the winged "C"s though.
  9. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Will KT88's fit in an SVT? Never tried it but I thought I heard that wide bottle tubes wouldn't fit in an SVT. Am I hallucinating again or is that accurate?

    Honestly, I don't see what's so bad about the EHX tubes that come stock in the SVT CL and SVT VR. EHX and Sovtek tubes have always been pretty reliable for me but they have this bad reputation. I don't get it. Am I the crazy one?
  10. Nothing "so bad EHX and Sovteks", the winged "C"s are just a better sounding longer lasting tube. You maybe correct about the wide bottles, I know this is true with the SVT-2 series and 3 non-pro.

    EHX and Sovteks do have a higher failure from open market sources (maybe end manufacturers dumps?).
  11. someparts


    Nov 22, 2010
    I've got the stock Sovteks in my USA made VR and Winged Cs in my SVT-II NP, and no complaints tonewise on either. Both sound great but I wonder if the VR would gain any of that furry quality that the SVT-II has going on....I guess I'm saying the Sovteks seem to have a cleaner harder sound but there are two slightly different preamp sections on the two amps so hard to say.

    It's not like I have 4 sets of 6550s laying around to do a shootout but that would be fun. I have to say when the VR needs a new set they'll be Winged Cs.
  12. Hi.

    I decline to answer about Your craziness, or the lack of it ;), but something that's a somewhat regulated and controlled supply (of tubes in this case) to You, might not be so for others.
    Especially when switching continents.

    EH and Sovtek have always been the "lower-end brands" over here, even though most of the companis that match tubes tend to use 'em.

    I do agree that the Red-connection won't help any, but overall, the quality has been pretty inconsistant over the decades. Sure, You may get a few decently matched sextetts out of, say, 100 raw tubes, but what's the point really? When all the selecting is done, the cheapo sextett costs about just as much as a "quality" one would. And the company is left with a lot of pairs and single tubes that are not so desirable, at least when talking about 6550 or KT88.

    Sure, the raw tubes are cheap, but taking into account all the hassle, and the shorter life expectancy compared with the more reliable brands, hardly worth it.

    Having independent bias controls for every tube turns the table completely around though, if You ask me that is. The un-avoidable early bias drift of less than 48 hour burned in tubes can be corrected individually, an unsettling tube can be discarded before it shorts out, periodical checking will reveal dying symptoms early on, etc.

    The EH KT88 is about the worst that there can be, if the ones in my amp are any indication that is. The mica doesn't touch the glass until the leads have shorted out (which was exactly how my amp arrived back in the day).
    How's that for quality or even decent engineering?

  13. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    My '07 VR is still running it's stock Sovtek 6550's and it sounds as good as it did when i bought it. maybe it's just me, but i haven't had much luck with the winged C's. after a while, all of them that i've owned developed noisey internals (rattling inside).

    my favorite sounding (and most reliable) replacement for RI 6550's have been valve art's KT100's.
  14. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    So Sam, you're saying that since EHX is American that we get the pick of the litter? Well that certainly is good to know. I'll be more inclined to try them again when I need tubes ;)
  15. Hi.

    LOL, not because of the companys American origins, but does EH really make tubes? Or did they in the past?
    In the 80's and 90's their tubes sold here at least used to be re-branded Russian tubes (just as GT's), and the ones in my Chinese mfg amp looks a lot like the common Chinese "KT88"'s.

  16. hermanski


    Dec 18, 2011
    In a live stage setting, you won't be able to tell the difference anyhow. I asked a similar question in a different thread about T/E gear and the TL 072 chips, and got a response similar to the one I gave you. But, I digress, I have had a bunch of tube amps, guitar and bass and for bass, stick with what the machine calls for. Switching tubes is a pain in the ass expensive, and the advantages are not really worth it.
  17. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Shuguang KT88 are new Chinese ones, but they are pretty good and far from expensive. New valves are starting to catch up. KT88s draw a little more current than 6550 which might account for some people saying KT88 are unreliable in SVT as that would be harder on the power transformer, but I noticed no-one that complained about unreliability could actually identify the problem caused.
  18. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    I had one in my V4 that developed a rattle inside, but that's out of three sets of 4, a set of 6 that was in my SVT-CL, and set of 6 that's in my current SVT, and the set of 6 that came with my SVT (I re-tubed while doing caps, etc, to have a fresh set). So one tube out of 30? Still a small sample size, but I've been happy with them.
  19. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Mike Matthews was pretty instrumental in getting a lot of those Russian tube mfg'ers started up and financed. Don't know if he directly owns the factories, but he's a huge player and probably the biggest factor in getting tubes produced again after all the American and European factories shut down.
  20. Clammy


    Nov 3, 2008
    Ottawa, Canada
    Endorsing Artist: Neal Moser Guitars, DR Strings
    FWIW, I am running an octet of Tung-Sol 6550 reissues in my Marshall VBA 400, and I like them a lot! They sound great and are priced reasonably.


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