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  1. #1
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    Question KT88 or 6550 amp tubes?

    Daniel Barnum has generously given me a Jolida 502 integrated amp, which, if I can repair (he said just one burnt out resistor needs to be replaced), I'll be needing to buy a full set of tubes for.

    There are so many different opinions, and, how do I sort out the listeners from the people that work for these companies who post in forums saying "this *** tube is great!"...

    As far as I can tell, KT88 and 6650 tubes are interchangeable? I need a set of four, so I guess it's best to get a "matched quartet". I don't know why it surprised me, but I just saw today that Parts Express sells tubes!

    Here are some I'm considering:

    Electro-Harmonix KT88: http://www.parts-express.com/pe/show...number=072-809

    Electro-Harmonix 6550: http://www.parts-express.com/pe/show...number=072-824

    Sovtek KT88: http://www.parts-express.com/pe/show...number=072-494

    I haven't even begun to research the other two types of tubes I need (1 pair of each): 2 x 12AX7A/ECC83 pre-amplifier; 2 x 12AT7/ECC81 power drivers

    I am sooo curious to hear what this tube amp will sound like compared to my Onkyo receiver! I hope I manage to get it working.

    I should bring the amp to a DIY event then we could do a solid state vs tube comparison?

  2. #2
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post
    Daniel Barnum has generously given me a Jolida 502 integrated amp, which, if I can repair (he said just one burnt out resistor needs to be replaced), I'll be needing to buy a full set of tubes for.

    There are so many different opinions, and, how do I sort out the listeners from the people that work for these companies who post in forums saying "this *** tube is great!"...
    Here are some opinions:

    http://www.hometheaterhifi.com/volum...on-6-2002.html

    http://www.jacmusic.com/KT88/kt88.htm

    For current manufacture I prefer the Tung-Sol 6550 reissue by New Sensor

    12A_7 info:

    http://www.vacuumtubes.com/12ax7.html

    http://www.vacuumtubes.com/12at7.html

    http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html (EDIT) this is a guitarists take on the sound of various tubes. It is good for gleaning characteristics of each type...

    Tube rolling is half the fun

    Here is a schematic link:

    http://www.geocities.com/free_schema...a/sj-502a.html

    You can run any of these in that amp:

    KT66, KT77, KT88, 6550, 6L6 variants, 5881, 6V6 and if there is a jumper between pin 1 and pin 8 you can run EL34's, too. Just make sure that you bias for every tube type. Also, some of these tubes draw a LOT of heater current. like the KT66. Check the running temperature of the power transformer. It will get warm but shouldn't get screaming hot.

    HTH

    Dave
    Last edited by dbe; 03-09-2009 at 12:38 PM.

  3. #3
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    Default Re: KT88 or 6550 amp tubes?

    Dave, thanks for the input. I wonder how much difference there really is in the sound? I don't doubt that there's a wide variety in the quality of construction.

    I'll read through those links that you sent.

    In particular, thanks for the information about the different types of tubes I can use. I want to stick with types that will work well with the Jolida amp. Don't want to try any that draw more current for the heater plate than the amp can handle easily.

  4. #4
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post
    I wonder how much difference there really is in the sound?

    I want to stick with types that will work well with the Jolida amp.
    There are some substantial differences in sound between types, less different within type.

    6550's are powerhouses that have full spectrum punch, KT88's tend to have great bass with slightly recessed mids. EL34's have terriffic midrange at the expense of LF extension. Of course these are broad generalizations, but seem to hold true for amps that have good primary to secondary matching in the output trannys.

    The amp was designed around EL34 tubes as standard. JJ has some great ones.

    My advice is to stay away from Ruby tubes in general.

    Have fun.

    Dave

  5. #5
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    Default Re: KT88 or 6550 amp tubes?

    Christopher,

    I ran KT88s and 6550 tubes in the 502. I prefer the 6550. In that amp and very specifically that amp, I found the 6550 be more liquid and musical overall. The KT88 had a more slam in the midbass and bass, but I never felt it conveyed the music as effectively as the 6550.

    Just my 2 cents.

    I hope you enjoy it.

    Very Best Regards,

    DRB

  6. #6
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    Default Re: KT88 or 6550 amp tubes?

    A crazy new universe of audio bankruptcy;
    http://thetubestore.com/teslakt88.html
    The JJ tubes are supposedly to glow blue due to the Belgian blown glass.

  7. #7
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    Default Re: KT88 or 6550 amp tubes?

    Could someone rank which tubs affect the sound the most in order? This amp uses three types of tubes - 4 "power tubes" and 2 each of 12AX7 / 12AT7
    Quote Originally Posted by drb View Post
    I ran KT88s and 6550 tubes in the 502. I prefer the 6550. In that amp and very specifically that amp, I found the 6550 be more liquid and musical overall. The KT88 had a more slam in the midbass and bass, but I never felt it conveyed the music as effectively as the 6550.
    I received the amp today, thank you. The FedEx guy was saying something about how heavy the box was.

    Which KT88 and 6550s did you try? This is what I found reading links:

    "Electro-Harmonix KT-88:

    When I reported the findings of this tube comparison to Bob Bergner of RB Audio (http://www.rbaudio.com), he repeated an oft-heard assertion that a manufacturer's KT-88s always sound better than their 6550 equivalents. Knowing how jazzed I was about the E-H 6550, Bob immediately contacted various distributors, and learned that Electro-Harmonix had just begun producing KT-88s.

    As of mid-June, 2002, many tube distributors that carry Electro-Harmonix have their KT-88 on backorder; I obtained my quad directly from Bob at RB Audio. This tube looks identical to the E-H 6550 except for a change in lettering.

    Simply put, in my amp, I find the E-H KT-88 superior to the E-H 6550. It offers more color, more depth, more refined highs, and a tighter bottom end. The sound is richer, fuller, and more exciting."

    ( http://www.hometheaterhifi.com/volum...on-6-2002.html )

    But... Maybe the EL34 sounds even better? At the moment, I can only buy one set of basic tubes. Maybe in a few months I could try something else, not sure. To try EL34s instead of KT88/6550, I would need to just connect a wire between two pins on the EL34? Or does some other mod have to be done to the Jolida?

    From several different sources that I read, the KT88s sounded like they'd be better/were prefered/would be more suitable for me, but, DRB liked the 6550s better in this particular amp? Maybe it depends some on what speaker you use? Would the KT88s be more likely to have enough power to handle full range 3 way speakers than the 6550s?

    Quote Originally Posted by dbe View Post
    ...The amp was designed around EL34 tubes as standard. JJ has some great ones.

    My advice is to stay away from Ruby tubes in general.
    I thought the 302 comes w/EL34 tubes and the 502 comes with 6550 tubes?

    I read a comment about Ruby tubes having "thin glass" and one came apart when the guy pulled it out of the socket - I'd like quality construction, well built, and something that will not degrade quickly with use, so I'm inclined not to get Rubys. I like reading about ones that have Gold plated components inside the bulb - but is that just a marketing gimmick?

  8. #8
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    Default Re: KT88 or 6550 amp tubes?

    EH KT88s are good tubes. I had a quad for a few months, but was never truely satisfied with them. I began with sovtek KT88s, and liked them for the bass, but the mids seemed a bit lacking IMO. I finally purchased a quad of SED KT88s. The only new production KT88s I have not heard is the JJs, but I hear they are very nice.

    The New issue Gold Lions sound very nice as well. If it were me and you are confident in fixing the amplifier, I would buy either the SED Kt88, or the Gold Lions. They are incredible sounding tubes with excellent all around sound.

    As far as 6550s are concerned, I have used many of them as well, but with a little less variance in sound. The Sovtek tubes are not quite as bad in the 6550 varieties. The Plastic based WD model being my least favorite, and the WE being a little better tube in over all sound.

    The EH, again is a great tube, but I prefer the new issue SED 6550 over it as well. The SED line of tubes thusfar has failed to dissapoint me at all in SQ and consistency.

    Hope this helps.

    Blair

  9. #9
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    Default Re: KT88 or 6550 amp tubes?

    I guess SED/Sovtek/Electro-Hamonix are all the same company now?

  10. #10
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    Default Re: KT88 or 6550 amp tubes?

    Not so sure about HiFi amplifiers, but I've built a few tube guitar amps and have worked on a few as well. A friend of mine needed some repairs on an Ampeg V4 with a quad set of 6550s in it. This amp was originally used by big bands in big venues because it's loud and clean. Now, the original tubes I think were 7027s, but the 6550s in the V4 - golly Miss Molly are truly loud and clean.

    That Jolida comes with 6550s originally, right?

    The biggest guitar amp I built was a V front twin with a pair of 12" Eminence Legend V12 speakers and a mostly Marshall-style amp with a pair of Sovtek E34L power tubes. I used some pretty clean iron, more of a HiFi transformer and my Fender Tele really jangled nicely with a very vintage Fender sound. However, if I wanted crunch, I had to jack the gain up and drop the main volume - it sounded great, but the thing was way too loud to turn up and overdrive the back end. I actually had it setup as a footswichable channel switching amp so you could set one channel clean and one dirty and switch between the two with your foot - but I digress.

    It'd be real fun to get a few sets of tubes and sit and listen to the differences.

    By the way, you're probably already aware, but don't be stickin' yer fingers all up inside the chassis - even if she's unplugged and off. Those voltages truly are dangerous and a good amp will store a nasty whollop in the power supply filter caps - so unplugging it doesn't necessarily mean it's safe. I build my amps with a drain circuit so that when the power is off, the caps are bled out through a big resistor.

    The old TV repairman trick is to stick one hand in your back pocket while you work on the thing - that way you don't inadvertantly create a circuit from one hand to the other right through your chest.

    Rock on!

  11. #11
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post
    I guess SED/Sovtek/Electro-Hamonix are all the same company now?

    Yes, New Sensor.

    Blair

  12. #12
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by blair View Post
    Yes, New Sensor.

    Blair
    Source?

    I know they make EH, but I think Sovtek is a separate company.

    NK
    I'm just that guy. www.sru.edu Rock Solid.

    "It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion."

    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  13. #13
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    Default Re: KT88 or 6550 amp tubes?

    Not too much time to post, but look here:

    http://www.newsensor.com/

    It is the entire New Sensor lineup.

    Blair

  14. #14
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by JRT View Post
    In your shoes I'd be very inclined to try the KT90EH from Electro-Harmonix, a slightly larger replacement for the 6550 and KT88.

    http://www.tubedepot.com/eh-kt90.html
    http://www.tubezone.net/pdf/kt90.pdf
    http://www.ehx.com/products/kt90
    How well do you think the KT90EH would work with the Jolida 502?

    The Sovtek KT88 I can get for under $100 for a quartet.

  15. #15
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    Default Re: KT88 or 6550 amp tubes?

    Here are pictures from the inside:







    Larger pictures here: http://www.flickr.com/photos/critofu...7615096684817/

    EDIT: I forgot how to read resistor bands (well, forgot what colors mean which, or which end to start at) I guess I will have to look at the schematic while I'm less tired, but does anybody know what value that is off the top of their head? And, maybe, why it burnt out?

  16. #16

    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post
    Daniel Barnum has generously given me a Jolida 502 integrated amp, which, if I can repair (he said just one burnt out resistor needs to be replaced), I'll be needing to buy a full set of tubes for.

    There are so many different opinions, and, how do I sort out the listeners from the people that work for these companies who post in forums saying "this *** tube is great!"...

    As far as I can tell, KT88 and 6650 tubes are interchangeable? I need a set of four, so I guess it's best to get a "matched quartet". I don't know why it surprised me, but I just saw today that Parts Express sells tubes!

    Here are some I'm considering:

    Electro-Harmonix KT88: http://www.parts-express.com/pe/show...number=072-809

    Electro-Harmonix 6550: http://www.parts-express.com/pe/show...number=072-824

    Sovtek KT88: http://www.parts-express.com/pe/show...number=072-494

    I haven't even begun to research the other two types of tubes I need (1 pair of each): 2 x 12AX7A/ECC83 pre-amplifier; 2 x 12AT7/ECC81 power drivers

    I am sooo curious to hear what this tube amp will sound like compared to my Onkyo receiver! I hope I manage to get it working.

    I should bring the amp to a DIY event then we could do a solid state vs tube comparison?
    Without my knowing which version of the 502 you have (I have a 502BRC, which has the remote & EZ Bias options), please take my comments with a grain of salt.

    For this amp the 6550 and KT-88 are functionally interchangable.

    Jolida currently bundles the EH6550 with the 502B series amps. I understand that this wasn't always the case but I don't know what was originally used nor at what point they switched over to using this particular tube, but it is what what shipped with my amp.

    I haven't heard the Sovteks in a 502-series amp so I can't comment on their performance, although they are widely regarded as being quite durable at the expense of some performance.

    I'm currently using the following:

    JJ Tesla KT-88 (matched quartet)
    new-issue Tung-Sol 12ax7, matched and balanced pair
    NOS Mullard CV4024, matched and balanced pair

    I was happy with the performance of the EH6550s and the stock Jolida-labeled 12ax7 and 12at7, but I found the combination I'm using now opened up the soundstage noticably and improved the midrange vs. the stock configuration and I'm quite happy with where I'm at right now and I hope that you'll find my info useful if for no other reason than as a reference point.
    As you point out, there are a lot of different opinions about what would work best. Good luck in your search!

  17. #17
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    Default Re: KT88 or 6550 amp tubes?

    The amp you have originally came with some inexpensive 6550 tubes and preamp and driver tubes. I put NOS JAN and Brimars in the amp with KT88s (I cannot remember what brand) While I enjoyed the sound I prefered the overall "liquidity" of the 6550.

    This is very nearly a first production run of the 502. I called Jolida some years back and they were shocked when I read off the serial number they said it was one of the first ones they ever made. That is all I know. I enjoyed the amp for many years. It was a good standby until the resistor blew and I decided to move.

    Best Regards,

    DRB

  18. #18
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post
    I should bring the amp to a DIY event then we could do a solid state vs tube comparison?
    I wont speak definitely until Wolf and I agree. Iyou let us know ahead of time we could find a way to work those into the InDIYana either fri or sat.

  19. #19
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post
    Here are pictures from the inside:







    Larger pictures here: http://www.flickr.com/photos/critofu...7615096684817/

    EDIT: I forgot how to read resistor bands (well, forgot what colors mean which, or which end to start at) I guess I will have to look at the schematic while I'm less tired, but does anybody know what value that is off the top of their head? And, maybe, why it burnt out?
    Do you have a pic of the schematic we can see?

    It would help, or at least a good picture of the bottom of the board showing where the different colored wires go?

    Blair

  20. #20
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    Default Re: KT88 or 6550 amp tubes?

    Quote Originally Posted by critofur View Post

    EDIT: I forgot how to read resistor bands (well, forgot what colors mean which, or which end to start at) I guess I will have to look at the schematic while I'm less tired, but does anybody know what value that is off the top of their head? And, maybe, why it burnt out?
    3.3K and it probably died from a combination of old age and being marginal in value. I would use a good 10 watt resistor here, like an Ohmite 40 or 80 series. A low noise resistor is important due to the following stages being used to supply the front end of the amp.

    Dave

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