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Best 6L6/KT66 for my Bassman 135?

Discussion in 'Amps and Cabs [BG]' started by BassGreaser, Jul 13, 2005.

  1. BassGreaser


    Aug 22, 2002
    Austin, TX
    I'm looking at new power tubes for my Bassman 135 as it still has it has some old cheap chinesse tubes in it. What are some of the best 6L6's, or KT66's tube for this head?
  2. Rockbobmel

    Rockbobmel Supporting Member

    I Put JJs in mine.
  3. I use EH or JJ most of the time. But they aren't the best, just good tubes reasonably priced. If I wanted the best I would be saving up the bucks for some NOS Mullard, or JAN Phillips or RCAs or GEs. If you want the best, check out this website http://kcanostubes.com/content/Default.asp
  4. anyonefortennis

    anyonefortennis Supporting Member

    Jun 28, 2005
    Lincoln, NE
    HP Groove Tubes for Kt-66. They have alil extra oomph for bass.
  5. BassGreaser


    Aug 22, 2002
    Austin, TX
  6. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    Don't use Groove Tubes 6L6s in there. I had them in there and they fried in under a year. That bassman 135 was really hard on tubes. I do regret selling it, though. :bawl:
  7. DaveMcLain


    Jun 19, 2005
    Cuba MO
    I would use the Groove Tubes 6L6GE, that's their own version of the GE 6L6 from years ago, I think it's the best avaliable right now. Groove Tubes bought the tooling when GE closed it's tube factory in Owensboro KY and they now produce the tubes in their own factory in the US. Right now I think the only models they make are the 6L6GE and the 6CA7. There are many other 6L6's that Groove Tubes sells including Chinese, Russian and Slovakian but the GE version is the real deal..

    In our Marshall amps I'm using their version of the KT66, the KT66HP. This tube is only avaliable from Groove Tubes and is made in Russia on their own tooling. The bottles are huge and they might not fit in your Fender, it might pay to measure and then e-mail Myles Rose and ask him if they will fit or not, if so, they will sound great and they will handle the over 500 volt B+ of that amp ok, as will the 6L6GE.

    Your Bassman probably came with the old Sylvania STR 6L6, I think it was the STR 687. An STR was a "special tube request" designation and those were designed for Fender and designed to be used in guitar amps esspecially combos. In my opinion they were the BEST 6L6 in a Twin Reverb or bass amp but finding new ones today would be pretty tough. Peavey, Mesa and others also sold that tube before about 1994 when the supply ran out.

    I used to say the Sevetlana 6L6 was most like the Sylvania STR tube and before 2002 they were, but not any more. The Peavey power amp that I was using back then came with the Sylvanias(1993) and I tried lots of different output tubes in that amp, Chineese, straight bottle and "coke", Tesla 6L6 and Sevetlana in about 1997. They sounded awesome and they lasted a long time, about as good as the Sylvanias that were OEM.

  8. That's what they want people to think, but the tubes are made in China. If you'll notice, they say the tube is either 90 or 95% US content depending on how bold they feel that day.

    It IS a good copy, but you can buy the SAME tube from Ruby for half of what GT sells it for. I have tons of old US 6L6GC's and even a few 7581's; I think KT66's are the way to go for a Bassman 135. There is nothing special about an old GE 6L6 regardless of what Groove Tubes' ads say.

    Aspen Pittman is REALLY prone to exaggeration. That tube is nothing but a Sovtek KT66. Groove Tubes doesn't own ANY tooling. They also made that claim about JJ/Tesla KT88's they rebranded for years until they were called on it by JJ's distributor.

    'STR' means 'special test requirement,' at least that's what my boxes of them say. If you're looking for that particular tube, its latter day derivative, the Philips 7581 is the same thing, but I still think you'd be better off with KT66's.
  9. DaveMcLain


    Jun 19, 2005
    Cuba MO
    I have no first hand info on Groove Tubes production, I don't live in Southern California so I can't pay them a visit personally, but here's some info from Myles Rose's website:

    The original GE 6L6 was perhaps the music world's most beloved power tube. It was used by scores of
    USA manufacturers during the Golden Era of US made tube amplifiers. Both the legendary McIntosh Hi
    Fi amps and Fender guitar amps commonly used this tube from the early 1950's through to the mid
    1970's productions. This was likely the tube used by Jimi Hendrix while recording thru the Fender Twin
    Reverb amp he commonly used in studio, as well as the tube used in Carl Perkins' Fender amps while
    recording for Elvis. General Electric discontinued production of receiving tubes in the late 1980's, and
    sold their entire remaining production line to Richardson Electronics of Illinois.

    The new USA tube adventure:

    In 1998, Groove Tubes purchased from Richardson the original critical materials and machines GE used
    to produce both the GE6L6 and GE6CA7 (aka:EL34), along with the original production processing
    formulas. In other words, Groove Tubes was able to acquire the the recipe, the original ingredients,
    and the kitchen too! The adventure had begun.

    Next, several original GE vendors were enlisted to faithfully reproduce many of the internal
    components. For example, the company who made the original mica insulators has provided the
    identical part, on new tooling from original GE drawings. Also, the special plate designs are made on
    the same vintage 4 slide machines and are identical to the original parts, using the original GE plate
    material that is no longer in production. GT was able to purchased enough original GE plate material for
    many years of production. This special multi layered alloy formula appears a soft dull gray after heat
    processing and give this tube it's soft, warm tone...as well as contributing to it's superior power
    performance. While currently, some of the processing is located "off site" and will continue there until
    all processing clearances can be arranged for the San Fernando factory, eventually plans are to do all
    processing under the GT roof.

    However, the internal content is now more than 90% USA origin (Incidentally, this content ratio is similar
    to to the original content of the GE tube as GE also used off site processing). It has been almost 4
    years of hard work and significant financial investment in tooling and setup to be able to release the
    final product, but the wait was worth it.

    Technical Details:

    The GT6L6GE tube is a beam tetrode, although it is also commonly referred to as a Beam pentode. It
    has a maximum anode dissipation of 25 watts when used in a common Class A/B circuit design. It is
    highly recommended for replacement for all 6L6/KT66 /5881 type audio amplifiers for superior fidelity
    and improved power output performance, especially in musical instrument amps but as well for High
    Fidelity reproduction amplifiers.

    This tube is being made in limited production runs in order to control quality and to achieve the
    original high performance specifications. Therefore, it may be some time before production "ramps up"
    to allow for general distribution into the worldwide tube market. Meanwhile, is currently only available
    from authorized Groove Tubes dealers located in the USA and 34 foreign countries in performance
    tested and matched Duets @ $90 and Quartets @ $180 (Singles, Sextets and Octets available upon

    I have been using Groove Tubes products since about 1985. I have been working with amplifiers and musicians

    Over time I have heard comments in regard to the higher cost of Groove Tubes own tube offerings, and comments
    that they sell the same tubes as everybody else and just stick their name on them. In some cases, the do sell the
    same tubes, but the GT logo does not go on the tube until the tube goes through their own unique testing process.

    On the subject of the same tubes, there are differences worth noting. Many tubes are made by the world's tube
    factories to specific GT designs and specifications. Some of these are the KT-66HP (which at first glance looks
    much like the Chinese variant, but is not made in China), the GT-E34LS which comes from the JJ factory but is not
    the same tube as the JJ E34L (look at the plate assembly), notice the heat sinks on the plates of the GT version),
    and other tubes such as GT's own, USA self made 6L6GE. The KT-88SV is a different tube in regard to plate
    assembly as another example. These are all tubes built off GT developed and produced tooling. UPDATE as of
    January 2004: On the horizon is the GT-6CA7GE and 12AX7M. See elsewhere on this website for info on
    these and their progress.

    For tubes that you may think are the same, look at the bases. GT re-bases many of their power tubes with a
    different assembly. Look at some other companies blunt pins with dipped coatings. Feel the resistance when you
    plug those into your vintage Marshall or Fender as the female inserts in the tube sockets either feel like they are
    being deformed, or just as bad, the insert comes out of the socket? GT uses polished and tapered pins that are not
    pot metal. This is yet another change often overlooked. Vintage tube bases are a lot happier with these pins.

    This is not the early 1960's anymore, and tubes are no longer widely used in medical equipment, scientific
    measurement equipment, or the Minuteman missile program. Quality control is not what it was four decades ago.
    In the past, a 12AX7 at 250 plate volts with a 2 volt bias would produce 1.2mA. Today, even the same maker, same
    batch, and run, will have tubes that vary from 0.6mA to about 1.8mA. Over 80% of these fall at below 0.9mA. This
    is one of the reasons that some of you have put new preamp tubes in your amp, only to have it sound worse than
    before. Maybe you had a 1.1mA tube in V1, and the new tube was 0.7mA. Groove Tubes has less than a 50%
    acceptance rate on their preamp tubes. The are tested for low output, microphonics, and noise. They carry a 180
    day (6 month) warranty. I found other vendors in many cases had a high degree of low output, microphonics, and
    even one of the two sides of the triode not even working. Most of them replaced these tubes, but it took time and
    effort to send back the bad tube (after making a call or two, or sending letters), and then waiting for the "new" tube
    to arrive. It became quite obvious, that certain vendors did little more than put the tube in a box and ship it.

    Who knows......
  10. BassGreaser


    Aug 22, 2002
    Austin, TX
    Pyscho which KT66's do you suggest for the best sound, and reliabilty? Why do you suggest KT66's?
  11. Myles Rose is a GT rep, not exactly an unbaised source, and besides, you missed the most important part:

    Wanna guess where that "off site" processing is? I have seen PICTURES of them making the tubes in China.

    The next part is an outright lie-

    I know the quality control manager for GE at the Owensboro (which GT can't even SPELL right in their ads) plant in the late 60-early 70's. GE bought their envleopes from Sylvania and that was the only extent of their 'outsourcing.'

    There is no such thing a a 'beam pentode'. The only time I've ever seen a beam tube referred to as such is in Pittman's book. His penchant for BS further manifests itself with statements like the following:

    Note that ANY production run of tubes is made 'specific designs and specifications.'

    No, it's a Sovtek, just like one you can get from New Sensor.

    ...which is identical, but the term "plate assembly" sounds all technical and whatnot so the average guy doesn't know that it's a bluff. What it means is 'Our' guts don't look like their guts, when in fact, they do.

    ... which you can see for yourself are ON the JJ's, plain as day, here.

    This is another lie. Here is what Eurotubes, JJ's exclusive distributor, IOW, the people GT buy them from, have to say about that: In fact one large re-seller has even claimed to have helped design the JJ tubes. This is pure fantasy or B.S. whichever you prefer.

    Get them from any dealer with a decent warranty. I'm partial to Ned Carlson, www.triodeelectronics.com

    I'd say go with the Sovteks since they do VERY well with their KT88. KT66's have a better plate current rating and will put out more power than a 6L6GC while sounding more even.
  12. DaveMcLain


    Jun 19, 2005
    Cuba MO
    I've never used their stuff exclusively or anything, but I have had good luck with their product in the past, particularly on some preamp tubes and I see nothing wrong with what they do, testing, matching etc. Most of the time I use tubes that I buy from New Sensor, I've had a few problems with them but not too often.

    I'm not sure about the 90% content argument, that would make it tough to say ANYTHING is made in ANY particular country. Look under the hood of an American car. Look under the hood of a Japaneese car, etc. components come from EVERYWHERE, I think electronics are like that to an ever greater degree I'm not sure if that's good or bad really....

    I have also used the KT-66 that Groove Tubes sells as the KT-66-HP the Russian version, I agree that that is a great sounding tube, no matter what origin, is it true then that it's better than the Chinese version, I have not tried that. Acording to Myles Rose and other sources, it's not so good above 500 volts B+, true or false?
  13. I have had EVERY set of every kind of Groove Tubes relabelled tubes become horribly mismatched conveniently as their six month warranty expires. That includes a set of old US 6550A's. The technical misinformation spread by that company is very damaging, and they have no qualms about outright lying. I'm not saying everything they sell is junk, just that as company policy, they are very dishonest and it irks me. Most of the tube myths you'll encounter have their origins in a Groove Tubes advertisement.

    I never bought direct because they are such a pain to deal with. All the "screened" New Sensor tubes that have come from the dealers I use have been excellent and the prices wreen't too much higher. I figure I'm paying someone else to burn them in and weed out duds.

    And I'm saying they are LYING. They justify calling the tube '90% US content' and 'US made' because they have the old plate material and assembly jigs, but that plate material is assembled on the old US jigs in CHINA. Mechanical stability is much more important than old material, because there is BETTER material now, but the assembly techniques are far more sloppy. That's why modern tubes have so many problems with microphony and shorts, and the highly skilled US workers who used to make the GE's made them BETTER than the dubiously skilled Chinese workers.

    They also lie when they say GE followed similar practices at Owensboro. Every part of the tube except the envelope was made at that plant. Audio tubes were a very small part of their production, and the tooling and material was all produced in-house to make large runs of tv and industrial tubes.

    Never used it.
  14. BassGreaser


    Aug 22, 2002
    Austin, TX
    Psycho what do you think of the old GE KT66's
  15. Neither GE, nor any American tube manufacturer, ever made KT66's. The "KT" series of tubes were the creation of MO Valve, A British Tube Company, who sold tubes under the brand Genelex. They were copies of American beam tetrodes like the 6550 (KT88), 6CA7 (KT77), and the 6L6GC (KT66). Prior to the mid 60's, large British audio tubes were pentodes: Mullard's EL34, but with the success of beam tetrodes for high powered audio, MO Valve copied the American tubes and improved their ratings. The "KT" stands for kinkless tetrode, because prior to the introduction of the beam tetrode, a "normal" tetrode would have a large current peak, a 'kink', in the plot of its transfer curve, making them all but useless for audio.

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