Groove Tubes 5751M

Discussion in 'Amps and Cabs' started by myles111, Aug 9, 2010.

  1. myles111

    myles111 Member

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  2. jaeger28

    jaeger28 Member

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    Hm, I have some Penta Labeled GT12AX7Ms and they have neither low gain nor do they sputter or make any noise. I love this tube, especially in amps that are on the bright side.
     
  3. Doug's Tubes

    Doug's Tubes Member

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    The GT-5751M is a re-labeled GT-12AX7M tube with even lower gain than a 5751.

    Bingo!
     
  4. Doug's Tubes

    Doug's Tubes Member

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    We got 350 pieces of this tube from Penta last May. Let's say the owner of Penta Labs and Aspin Pittman were close friends and business associates.

    This tube is what the GT-12AX7M should have been......
     
  5. Doug's Tubes

    Doug's Tubes Member

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    There's also a tube vendor out there somewhere claiming this tube is currently built for GT by JJ and charging $39 for them!!!:eeks

    Thanks for clearing up all the misinformation on this Myles!
     
  6. myles111

    myles111 Member

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    That is good news. Not all of the tubes were bad, just a very high percentage.

    In the case of the 12AX7M (tooling is the same as the 5751 is produced upon), they are the most inconsistent tubes of any type. Look in the last edition of "The Tube Amp Book" deluxe revised edition 2nd printing and look at the specs and data for the 12AX7M compared to all the other tubes listed. It is by far, the worst in the bunch by a very wide margin.

    Your 5751M is nothing more than a 12AX7M that failed worse than the already poor 12AX7M.

    But ... there are some great 12AX7Ms from the earlier runs. I used to love them in Tolex era Fender amps to tame brightness. I had a lot of clients that loved them in Marshall amps that were pre master volume.

    When you find a good one it is pretty terrific but finding one became more rare as production continued. You should also carry known good spares as the tubes of both type can fail without warning much more often than any other tube.
     
  7. myles111

    myles111 Member

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    Doug,

    I have not talked to the Penta folks in a while but they might have stepped in and ran with the design. Steve at Penta was the fellow who got Aspen involved in vacuum tubes in the first place. Steve is a great guy and has actual knowledge about tubes. If Penta took over the development I would not be surprised if they finally turned into something workable.
     
  8. myles111

    myles111 Member

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    Doug,

    The guy talking JJ is probably just confused or mis-informed. If you look at the current photo on the website it is indeed the Shuguang Chinese produced tube. Then again, it may be a very old photo as Fender does not currently silk screen tubes anymore, they put a sticker on instead ... faster, cheaper.

    I love to talk to the vendor claiming JJ is making the tube to get that info first hand. If the tube strays from the Mullard design with the compression fingers on the cathodes and the mica layer design then Fender would have to re-write their statement on their website in regard to the tube.

    I also do not think JJ would produce a one off brand of tube for anybody. If you want their stuff you buy their designs. If the long plate ECC803S was used in an attempt to replace the Chinese version I think many people would spot this pretty easily as the 803S is a distinctive tube visually.
     
  9. Mark Robinson

    Mark Robinson Member

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    So who's making 12A anything 7 that's worth buying these days?

    I have a mix of used old stock and some Chinese contemporary tubes in my Guytron, which has a crap load of tubes in it, and would like to purchase some current production, well tested tubes for it's seven available spots. I'm sort of chasing a gassy sound around, that's way down in DB but will doubtlessy get worse before it gets better.

    I've always been fond of long plate RCA and G.E. tubes and have some still but they have tons of hours on them and I don't feel like buying pulls and shakey provenance NOS anymore at todays' prices. Is a Telefunken really $100 dollars better sounding? Please say no..
     
  10. GDS Racing

    GDS Racing Member

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    I don't know about $100 better but I do like the Telefunken in the OD channel of my D-clone. It is smooth. I haven't tried it in a GT100 yet.
     
  11. Mike9

    Mike9 Supporting Member

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    I have a pair of early GT 12ax7M's and they aren't bad tubes at all. Not close to the Mullards they were meant to copy however - at least not to the Mullards I have on hand.
     
  12. myles111

    myles111 Member

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    On Telefunkens - I find them way too bright for my own taste in every amp other than a Dr. Z Carmen Ghia which has a different sort of tone stack. The long plate Telefunken can be physically microphonic in a lot of amps especially combos. Their reputation was built on stationary audio gear for the most part.

    On good stuff today ... there is some good things out there. I find the Tung Sol Reissue by the Sovtek folks / Mike Matthews is the most linear and consistent 12AX7 tube out there at the moment. In a long plate the JJ 803S is a nice offering and another long plate, the Sovtek 12AX7LPS is also a nice tube.

    The most important factor is selecting a good vendor. There are some great ones and some terrible ones. Some that I have used and continue to use with excellent results are:

    www.kcanostubes.com
    www.dougstubes.com
    www.tubedepot.com

    There are others that are great too but I listed these folks because they have never let me down and my clients also have very good things to say about them.

    Your Guytron (if one of the 100s) is a very complex amp with two completely different front ends. You will notice less difference in tube changes in this amp compared to a more simple circuit which has simple gain staging and a simple tone stack. Don't spend a lot of money on pricy tubes for this amp. There are many current production tubes that will work and sound terrific in the Guytron.
     
  13. lefty kwan

    lefty kwan Member

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    Wow,this thread opened up a can of worms.
    I have GT5751m's in the V1's of both my JCM800 4104 and my Pro Jr. Both amps sound great and have for a while. In the JCM800 the 5751m reduced the gain a bit but took a lot of the fizz out the preamp overdrive making the amp sound warmer and fatter. In my Pro Jr it a lso reduced the gain a bit, but took a lot of the compression out of the amp making a more open and punchy tone. No noise or staticy issues with both amps.
    I've used GT12AX7m's in the past and had a couple of really good ones but I also had a couple of bad one that were noisy,rattled and produced staticy crackles so I gave up on them...or so I thought. I now find out that I'm running GT12AX7m's that tested low relabeled as GT5751m's. I guess I have two good one's because they do sound good with no noise issues like I've previously encountered. But what do I do when they need replacing? Talk about bursting the bubble.
     
  14. myles111

    myles111 Member

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    Lefty,

    When you need to replace try a real NOS 5751. Less gain generally equates to less noise and this is one cool aspect of a 5751.

    You might find an NOS 5751 will give you the tone you like but they will last decades and be reliable with less worry.

    NOS 5751s are available and not all that pricy.

    As a bit of a guideline, most of the GT 5751s actually spec out gain wise as a 12AY7 (gain about 40 rather than 60-70 of a 5751) The 12AY7 was the front end tube in the Fender tweed bassman, tweed deluxe, bandmaster and super. The average 12AX7M in the runs over the last two or so years at GT had gain of a 12AT7 at best on average. This is about 70. Many tubes are in the 60 range. When the tube fell below 60 they were screened as a 5751M but the plate current is off the map (generally three times or more than spec) and the plate resistance and other factors are nowhere close to spec.

    It may have been better to market the GT 5751M as something like a 12UJ7. Some number that does not exist. Then it would not be compared. It could be said that it was a possible replacement for a 12AX7 type tube that just sounds different. That may have been the most honest approach.

    Hmmm ... I liked what I wrote above so I will probably copy it and paste it into my original blog entry.
     
  15. lefty kwan

    lefty kwan Member

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    Thanks Myles,
    you've got my OCD senses tingling. I guess when I get to NOS 5751 shopping I'll be looking for a brighter sounding one for the Pro Jr and a darker sounding one for the JCM800. Of the 2 Gt5751m's I have the brighter one is in the Pro Jr. Exchanging the tubes in the amps doesn't sound as good, the Pro Jr sounds a little dark and the JCM800 get's a little bright. Like I said previously, the amps are sounding really good presently... at least till read this thread. Ignorance is bliss.
     
  16. myles111

    myles111 Member

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    Lefty,

    Bottom line - your own ears and taste are the final judge. Your bliss comment .... very true in many cases:

    A few years back I had 4 GT-12AX7M's in my Twin Reverb in V1, V2, V4 and V5. I loved the sound of the amp.

    At one point at work (I was at GT in those days) a lot of complaints started to surface that described an issue that when the volume knob was turned down, the sound level would rise at some point while turning down the volume. In some cases when the volume was all the way down the amp would rise to a very loud level.

    I normally left my own amp set at about 3 on the volume on the reverb channel. Never changed it much at all. I went home and turned the volume down. Sure enough, at about 1.5 on the volume knob the level jumped to a very high level. My remedy was to leave the volume knob on 3-4 and thus, no problem.

    In a Fender Deluxe Reverb I also had some Ms that clicked and popped after the amp was taken out of standby. It did not help to warm up the amp for any period of time in standby first. It was more of a capacitance issue from such low plate resistance and the two sides of the tube not being well isolated. Various components interacting in some manner seemed to act like a capacitor in a way and there was a steady click-click-click for a few seconds, maybe up to 20 seconds. I liked the tone of the amp so I just left those in there as well and just let the clicking go away after a few seconds and then all was fine.

    So ... just play and be happy and let your ears be the judge.
     
  17. jerrydyer

    jerrydyer Member

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    exactly...why label something a 5751 if its not a 5751? cause the kids are talking about 5751's and someone saw dollar signs.........sucks. more confusion and mislabeling.
     
  18. myles111

    myles111 Member

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    Or .... why toss something in the trash that did not come close to making spec even though it shares none of the attributes of a real 5751? As you said $$$$$
     
  19. myles111

    myles111 Member

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    If there are any folks in the So Cal area that have any of the GT 12AX7M or GT 5751 tubes and would like to have them tested and traced I would be happy to do this at no charge. Drop me a note via email or send me a note on facebook if you are on facebook and we can set up an appointment.

    I do not mail things back and forth so you would have to be local enough to North Hollywood to bring the tubes into the shop. This would be done while you wait (and watch).
     
  20. lefty kwan

    lefty kwan Member

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    Too bad I don't live in the area because I'm quite interested in finding out how my tubes test.
    I have one GT5751 which you can faintly read underneath in white paint stenciled 5751 USA- this tube has the least amount of gain but sounds full.
    I have 2 GT 5751m's one of which sounds darker than the other one.
    The tooling between the GT5751 and the GT5751m's are slightly different. The GT5751m's have more gain than the GT5751.
     

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