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tube rolling 6v6,6v6gt's and 7408's

Discussion in 'Tube Audio' started by Jcricket, Feb 5, 2010.

  1. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    Hey folks, I have been messing with my new HK a300 tube amp. It is a 6v6 PP amp. Sound very good. I thought I would give it a try with several of the different tube sets I have. So far I have only tested three different sets.
    Ist up was a set of magnavox 6v6gt's made in japan. The clarity is very good. The highs and moids are very pronuonced. The lows are tight, but lacking.

    2nd up was a set of wesinghouse 6v6gt's. They were similar to the magnavox. They had a l;ittle better mids, a little less on the highs, and bas was about the same.

    3rd up was a set of HK 7408 tubes - WOW! The highs are very good, the mids are rich and warm, but the bass is very powerfull. The first two sets would not push the woofer to its ecursion limit. The hk's do so with ease.

    I didn't think there could be that much difference in tubes.

    So anyone else got some 6v6 tube experience to share. What is your favorite 6v6gt tube and why?
     

     

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  2. GordonW

    GordonW Speakerfixer Subscriber

    Messages:
    17,869
    Location:
    Marietta/Moultrie GA USA
    HK7408 == Sylvania, at least if yours are like mine. Look for the number "312" on the base of the tube somewhere.

    I also like GE 6V6GTA/7408 (they're the same tube inside) in mine. Can't tell much difference between them and the Sylvanias, other than the GEs glow pretty blue on the outside of the glass, and the Sylvanias don't (and as such, that's why the GEs are currently in the amp. :D ). Both are excellent.

    What manufacturer code is on the Magnavox tubes? 274? 322? I've seen RCA (274) and Tung-Sol (322) in those Maggies, among others...

    Have all these tubes you put in, been tested for emission and other parameters on a tube tester? Sometimes, the differences you mention, can be dependent on how much "life" the tube has left...

    Regards,
    Gordon.
     
  3. Elliot Thompson

    Elliot Thompson Well-Known Member

    Messages:
    896
    Location:
    New York

    A few years ago, I was on a quest to find the best 6v6 for high frequencies. I would imagine I invested over $1000.00 on ebay buying valves.

    For ultra high frequencies (17 kHz and above) Tung-Sol (Original) and Sylvania performed best for my requirements.

    Familiarise yourself with date and, manufacture codes. Also, don’t fall into the mindset that valves need to be replaced often. When they are showing signs of decay, you will hear it. No one can predict the lifespan of a semiconductor so valves are even more mysterious in this category. I’m using my oldest 6V6G (it was manufactured in the mid 1930’s to early 1940’s) and, they are used on a daily basis.

    If you did not know, 6V6G’s radiate less heat than 6V6GT/GTA since they use a larger casing. If your amplifier/receiver offers ample space try a few brands offering “the coke bottle” as well. There are also alternatives (CV509, KT63) that are the European version of the 6V6G to explore too.

    You have lots of options with the 6V6 providing, money is not the limiting factor.

    Best Regards,
     
  4. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    Yep, Itested all of the tubes on my sencor for emissions, shorts, grid leakage and lif.

    The maggies do not have a date code/manufacture code that I can see on the bass and the only mark I see is under the 6v6gt on the glass, it is in small print and says k00

    the westinghouse are 337
    and the hk are 312

    I have several more sets I am going to dig through and try.

    Elliot, I'll start searching out those brands/modesl as well. I appreciate the feedback
     
    Last edited: Feb 6, 2010
    rshadley likes this.
  5. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    just went through my stash,and found
    1. four matched magnavox 072's
    2. Three westing house 337 7408's
    3. one maggie 210
    4.two ge's marked 83-28/188-5 and 58-52/188-4
    a maggie 6W6 188-5
    these tube have all been tested as good and strong

    these tubes below have been tested as weak or questionable, but not bad
    1. one GE 6w6gt 18-5
    2. three maggie 6v66gt 210
    3. one ratheon 6v6gta labled usa jabo number m10


    I read that a 6w6 was sometimes interchangeable withthe 6v6 - true?
    Never tired it.

    Mark
     
  6. GordonW

    GordonW Speakerfixer Subscriber

    Messages:
    17,869
    Location:
    Marietta/Moultrie GA USA
    6W6 is a rough sub for 6V6, though not as much voltage handling (300v vs. 315v). It also required more bias voltage (which means it will idle at higher current than 6V6, everything equal), and draws MUCH more heater current (1.2 amps vs. .45 amps). It's also only a 10 watt plate, where the 6V6 is 12 watts.

    In the HK A300 amp... they run the 6V6 at near the max voltage. I wouldn't trust a 6W6 in it...

    Regards,
    Gordon.
     

     

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  7. Jcricket

    Jcricket not someday, but today

    Messages:
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    What in your opinon is the bes NOS 6v6gt/7408 tube avaialble, for under the price of a new car.
    I owuld like all opinions on this please.
    MArk
     
  8. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    I am trying to find jim mcshane - can't seem to pull him up on the mebers list. Anyone got a link to his pm?
    Thanks!
    MArk
     
  9. gearhound

    gearhound Lunatic Member

    Messages:
    10,115
    Location:
    Santa Fe, New Mexico
    LOL!!!

    Brimar, Mazda, and other European 6V6 tubes, can cost you a mortgage payment.
    Even black plate RCA's aren't far behind in price.

    NOS Sylvania, NOS Jan Phillips, & NOS GE 6V6 tubes can usually be found for "reasonable" $$$.....especially on flea-bay.
    I have a pair of NOS Sylvania's in my Webster 6V6 PP amp, and I'm quite satisfied with them.


    Steve
     
  10. Elliot Thompson

    Elliot Thompson Well-Known Member

    Messages:
    896
    Location:
    New York

    The 7408 were not made by a lot of companies. It was designed be one and branded by others. If you really want to explore 6V6, you’ll need to focus on 6V6 not 7408.

    Here are a few brands you can try:

    General Electric

    RCA (Bear in mind General Electric founded RCA and, their earlier models are just re-branded RCA)

    Raytheon

    Tung Sol

    Bendix (Tung Sol made the 5992 for Bendix at one point so bear that in mind)

    Sylvania

    Mullard

    Westinghouse

    Macroni of Canada (Westinghouse made Marcroni of Canada Valves at one point)

    Macroni of the UK

    GEC (General Electric of Canada)

    That is the few I remember at the moment without literally looking in my valve box. A lot of the esoteric brands are not worth it in my point of view.

    Sound is subjective so I would strongly you buy a few and make your own judgement. If you are very critical to sound (as myself) it will be the hardest thing finding the answers on the Internet from those you’ve never formally met when, sound is the topic of discussion.

    The Loudspeakers, the music format, the persons frequency range in terms hearing capability in addition to how one perceives sound are just a few things why it is always best to buy and listen for yourself.

    Best Regards,
     
  11. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    Hey Eliot, Thanks you for the feedback,
    A little info about myself.
    I have a very severe roll off over about 10k - I am deaf.
    I have a roll off over 7k.
    What I find is that many of the 6v6 tubes I have tried seem to have excellent clarity, but lack bass. I am looking for tubes that have that clarity and provide better bass.
    That being said, would therebe any recomendation you would have from your list.

    The speakers being used are Klipsch cornwalls with updated crossovers and the crites titanium ct125 tweets. My main amp at the momonet is the hk a 300.
    Not sure if that helps, but whatever you can recommend would be greatly appreciated.

    Mark
     

     

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  12. Jim McShane

    Jim McShane Well-Known Member

    Messages:
    505
    You can contact me through here:

    http://pages.prodigy.net/jimmcshane

    if the PM thing isn't working for some reason.

    BTW, a real contender for best 6V6 ever is the Tung-Sol reissue!
     
  13. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    Thanks JIm, sent an email.
     
  14. DENNYDOG

    DENNYDOG Addicted Member

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    Location:
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    Mark, thanks for starting this thread. I've been on the search for replacement 6v6's for the monoblocks. I wasn't sure if I wanted to spend what a lot of people are getting for a good quad of originals. It's nice to hear that the new Tung-Sol's sound that good. MarkW mentioned that in a thread you started last year.
     
  15. Elliot Thompson

    Elliot Thompson Well-Known Member

    Messages:
    896
    Location:
    New York
    It helped a lot. :thmbsp:


    Knowing your frequency limitation in terms of hearing is the first step of achieving the sound you are aiming for.

    Your speakers are very top heavy based on having a compression horn. They are very efficient however, un-manageable from 1 kHz – up. This is where the compression horn overrides everything.

    Power is essential and, the 6V6 (in addition to 90% of the valves in the market) are under 20 watts. This affects your bass for you need power the drive.

    At 10 kHz you still enjoy sibilance from female vocals and, cymbals. However, with a compression horn in your klipsch loudspeakers, it will sound louder than those using a non-horn-loaded high frequency driver.

    Nevertheless. I would recommend RCA, GE, or Raytheon (Raytheon offers the most high frequency roll-off) for your 6V6 and, Mullards for your ECC 81, 82, or 83 pre-amplifier valves.

    Flat, sterile sound is not what you are looking for which most of those esoteric (Telefunken) fall under. Also, if you are using a vintage piece, take advantage of the tone controls. They were designed to alter the tonal characteristics of the sound as with the valves. Most of the bass controls in original valve equipment will offer anywhere from +15 to +20 dB if you turn the control to maximum. That exceeds transistorised audio equipment that range anywhere from +8 to +12 dB for your bass contour.

    The chart below is the frequency response of the cornwalls. The RCA or G.E or Raytheon/Mullard combination will fill in the gap where the Cornwalls are at it’s weakest. That would be within the 200 Hz regions in addition to 50 Hertz and below.


    [​IMG]






    Best Regards,
     
  16. Jcricket

    Jcricket not someday, but today

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    Location:
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    I am not sure what is in the monoblocks, I think they are maggie black plates. You'll know soon.
    mark
     

     

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  17. buickguy62

    buickguy62 Active Member

    Messages:
    218
    Probably over a year ago, I saw the following on a forum, can't remember where, but did copy it for posterity as I do work on the A300's. Maybe someone will recognize it.

    Understand that this was one man's opinion.

    I've owned a HK A300 for about six months. I had it fully restored prior to use. I've rolled about a dozen types of different power tubes through it. It is a terrific amp. The 6V6 sound is addictive and I don't think another tube can match it's treble performance (except perhaps it's cousin, the 6AQ5). Here are my opinions of different power tubes in the amp:

    In a class by itself: Mazda 6v6gt, 1950s vintage. I bought a NOS quad on ebay. Utterly terrific sound. This type was lauded by VTV in their article about the 6v6 a few years ago. Wish I could find a quad of Visseaux. This tube loves the A300. The Mazda can still be found NOS for around $70 a matched pair.

    Very good: Bendix 5992s, GE greyplate 7408s, GE greyplate 6v6gts. The Bendix have a unique sound. Very full and direct. The GEs are wonderful, consistent, and balanced. The GEs can still be found at reasonable prices. I landed a pair of NOS the other day on ebay for $15. The 5992s are pricey and getting harder to find. I hear they last forever, though. Probably also in this category are Canadian GE smoked glass 6v6gty. Very rhythmic.

    Good: Tung Sol blackplate 6v6gts, GE blackplate 6v6gts, Westinghouse 6v6gts and 7408s. Decent sound but somewhat one dimensional. Not nearly the depth of soundstage of the ones above. Same goes for tonal accuracy also. Also in this category I would add US made GE6v6gty.

    Fair: All Sylvania 7408 and 6v6gt, CBS 6v6gty and blackplate. I had five different quads of Sylvania and CBS. All disappointed significantly. Flat soundstage, distorted tone. The Sylvanias are usually blackplates and look gorgeous, but are a huge sonic disappointment.

    I didn't try RCA because they are so pricey, price driven up by the guitar folks. I also haven't tried current production 6v6 yet.
    I found huge disparities in performance of this type of tube. I've sold off the good and fair performers.
    Preamp tubes:
    12AU7: Rolling this tube makes a huge difference in this amp. Most of the 15 or so tubes I tried were Ok. There were three clear winners: 1) Amperex 12au7 - 1960s bugle boy, made in Holland, 2) RFT 12AU7, 3) RCA cleartop. I suspect these are the same results many folks get from these tubes. This fits Joe's tube lore. The RFTs provide a tight, controlled sound and are probably my favorite. Most other US and European 12AU7 did a decent job, including current production. I didn't try any Chinese. I'm going to try Brimar 13d5s next.

    12AX7: Again, a dozen decent performers and some clearcut superior tubes: 1) RCA 5751 triple mica blackpate, 2) RCA dull blackplate, 1960s vintage, 3) Raytheon 12AX7 blackplate. Telefunkens lightened the sound too much. Mullards sounded off. The rest, mostly American 12ax7, sound pretty fuzzy and lowered image specificity. An honorable mentioned goes to the new Shuguang 12AX7S. These cheap little beautifes give a fat, warm, tone that matches the amp fairly well.
    I hope my biased opinion helps.
    The A300 is an outstanding amplifier.

    So, there it is for what it's worth.
     
  18. Jcricket

    Jcricket not someday, but today

    Messages:
    7,450
    Location:
    Littleton Colorado
    Eliot, Thannks again for he time an the info. I'll start my search and let you know how it turns out.
    Mark
     
  19. bronco

    bronco Active Member

    Messages:
    234
    Try some RCA black glass, black plate 6V6GT tubes. Definitely my favorite.
     
  20. Elliot Thompson

    Elliot Thompson Well-Known Member

    Messages:
    896
    Location:
    New York
    By all means keep me updated.

    There are not many 6V6 users on Audiokarma. It appears many are focused on guitar amplifiers when discussing this particular valve. Their concept on sound differs than I since they are focusing on achieving a high degree of distortion.

    Best Regards,
     

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