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How do I replace a tube?

Discussion in 'Amps and Cabs [BG]' started by chris h, Aug 8, 2002.


  1. chris h

    chris h Guest

    Jun 16, 2002
    Oxford, England
    I have opened up my HA3500 and want to replace the tube with probably a EHX or something, but how on earth do I get the old one out? Do I pull it, un-solder it, unscrew it?

    Thanks v much,
    Chris
     
  2. seamus

    seamus

    Feb 8, 2001
    Jersey
    No soldering or screwing, a little pulling. It's a combination of being gentle and firm simultaneaously.

    What I do is hold the tube near the base, and rock it back and forth a little bit while pulling it out. As you rock it back and forth a little, it should begin to unseat, making it possible to remove the tube.

    When putting the new tube in, I employ the same technique. First I align the pins. Then I begin with a little rocking back and forth again while easing the tube into place until it is seated firmly.
     
  3. camoe

    camoe

    Sep 7, 2001
    Lafayette, CO
    Just to add a bit...always use cotton gloves when inserting new tubes (or removing if you plan on using that tube in the future) as oil from your skin will degrade the performance of the tube.

    Peace
     
  4. seamus

    seamus

    Feb 8, 2001
    Jersey
    Yeah, that's not a bad suggestion. I usually just try and wash up really well before handling them.
     
  5. Tapp

    Tapp

    Aug 29, 2001
    USA, Mississippi
    "Just to add a bit...always use cotton gloves when inserting new tubes (or removing if you plan on using that tube in the future) as oil from your skin will degrade the performance of the tube."

    No disrespect but where did you hear this? I can't imagine a little bit of finger oil on the outside of a vacuum sealed glass bottle harming the performance of a tube. I would think the actual labelling would definitely be detrimental if this were the case.

    Now, I wouldn't go pulling out tubes after a dinner of KFC but really....

    Just rock the tube (just a little) in a rounding motion and pull it from the socket. When replacing, make sure the tube is lined up and rock it back in. With the many tube repairs I've done, I have never once worn gloves and have touched every tube; no harm that I've been able to tell.

    Tapp
     
  6. bben

    bben

    Feb 28, 2002
    Santa Fe, NM
    The white glove thing can't hurt, but is really for high-temp quartz filament bulbs. Audio tubes don't really get that hot where skin oil matters. I have some tubes that were my grandfather's, from the 1940s, that have been handled repeatedly, no problem.

    But, audio tubes do get hot enough to burn you, so I sometimes use gloves when doing a hot switch when troubleshooting or comparing. Always be sure the power is off when changing tubes, and unplugging the amp is a good idea, too. Even when unplugged, the power supply filter capacitors can have high voltages, so another good rule is don't touch anything but the tube itself.
     
  7. sounds like the same thing on the navigation lights on my boat, your not supposed to touch them with your hands. They are vacuum sealed and the glass is thin and very porous, the oils in your skin breaks down the glass thereby causing it to fail sooner. Put a light in last year with my hands and it lasted about two weeks, replaced it the way it should be and its still working.
     
  8. chris h

    chris h Guest

    Jun 16, 2002
    Oxford, England
    Righto, cheers. suppose it was probably a bit of a stupid question, but I couldnt find out anywhere else! I replaced the tube this afternoon and its working properly again. hooray.

    P.s I didnt use gloves!! DOH!!
     
  9. camoe

    camoe

    Sep 7, 2001
    Lafayette, CO
    "Don't worry about the gloves thing; it's complete BS."

    Really? Wow, you need to speak to some of our design engineers...we could save a lot of money with that advice. Seriously though, even though tubes in pres and amps don't get that hot. Oil and salt from your hands does not help the long term life of the tube...this is fact, not fiction. Can you hear the difference between a dirty tube and a clean one in a bass rig? Doubtfull. However, my comments were based on handling safety and overall life of the tube. It's just good valve maintenance. Careful with what you call BS if you really don't know.

    Peace
     
  10. camoe

    camoe

    Sep 7, 2001
    Lafayette, CO
    I'm not gonna get into any flame war with you. As far as my experience with tubes...i've been working with them since 1986. The design engineers I refer to work for Hitachi High Technologies Electron Microscopy division. I'm a field engineer for the same company/division.
    Although you may have never seen one fail after handling them does not mean that the life expectancy and/or stability of the tube has been altered. I've been involved in many long term tests evaluating the stability of tubes and like items (electron microscopes - the worlds largest and most expensive tube) and it does make a difference, especially to the stability of the tube. So either the Engineering schools I've been too, and Hitachi's design engineers are complete idiots or you could be underestimating the long term effects which possibly could never be noticed in many situations. I'll let this end at that.
     
  11. camoe

    camoe

    Sep 7, 2001
    Lafayette, CO
    "Hence, HIGHER operating temperatures.That electron microscope runs at signifcantly voltages which in turn generate higher temperatures. The HEATER voltage requirement for an electron microscope exceeds the PLATE voltage of most audio tubes! They're cooled with liquid nitrogen, too, if I recall correctly. What temps do your envelopes run? The average audio tube rarely exceeds 250 degrees. What AUDIO tubes do you have experience with?"

    I don't think you understand the theory of electron microscopes altogether. They don't quite work that way. I used an electron microscope as an example because it is a tube. It has a filament (varying types), an anode and a cathode. Potentials are applied and whola...an electron beam. LN2 is used in some cases for cooling of a stage/cryo trap, or for EDS detectors, nothing else. The reason why skin and salt affect the stability is because it affects the glass as it heats. The glass heating is not uniform and therefore affects the gasses (always gas inside tubes..just very little) inside the tube causing instability to the electron beam itself. All tubes, be they audio or not work this way.

    Previous to working for Hitachi, I worked with tubes of a variety of sources (signal generators, synthesizers, etc) in metrology labs. Perhaps you missed the comments on long term tests that have been completed on this matter.

    I'll make this simple. Stability, stability, stabilty. Oil and salt affect the stability of any tube over the long term operating life of the tube. Some tubes (determined by internal operating voltages, temperature, etc) are affected less or more than others...thats all i'm saying. Therefore it's good practice to use something other than bare skin for both safety reasons and extending the life and stability of the tube. I can't explain it any other way. If we disagree on this, fine. I'll continue to use gloves and you don't have too. We obviously aren't coming to a meeting of the minds here.
     
  12. camoe

    camoe

    Sep 7, 2001
    Lafayette, CO
    "So I know that they operate at temps and voltages that would melt/possibly vaporize audio tubes, require a separate coolant, are on the order of 150 times as large, but other than that, they're exactly like a 6L6GC or 12AX7, huh? I've never claimed any more than just a cursory knowledge of an electron microscope, but audio tubes, I know intimately."

    In a simplistic sense, they are like a 12AX7. I have no doubt that you know audio tubes intimately, that much is obvious.

    "So let me get this straight: The glass is only an insulating envelope surrounding an evacuated emitter, but what little gasses are left inside after vacuum pumping and getter flash are heated unevenly by the internal heater filament because of fingerprints on the OUTSIDE of the envelope?

    Heating the glass is only a SIDE-EFFECT of heating the cathode and ANY kind of internal gaseous heating that occurs from the glass will doubless be VASTLY overshadowed by the operating tempatures of the plates themsleves which are two to three times hotter than the glass EVER gets.

    I can buy gas interaction. Ionzied gas glows blue inside a tube. Its charge can affect current mildly. This only occurs in leaking tubes near the end of their operational lives or in the early stages of plate runaway as excess cathode emission charges the gas inside. The filament (6v) of a tube can nowhere NEAR approach the temps of an electron microscope. So how exactly would this gas be affected by fingerprints over the overwhelming larger heat source of the tube elements themsleves?"

    You understand more than I thought...my apologies. To make a long story short...what I'm trying to illustrate is that gas instability in the tube causes instability in the beam itself of the tube. Not to mention that heat instability also changes, in a slight way, the work function of the tube, causing emission variation. Any type of gas or heat variation will affect the performance of a tube to a degree. I think though we have a misunderstanding as to the degree of said instability. The tests I am referring to were conducted at two different places I have worked. The first being a test we conducted at the Areonautical Guidance and Metrology center. A lab that is one step below NIST in the metrology heirarchy. Here, highly accurate signal generators of various types were tested with thermal RMS voltage meters with resolution close to ppm and monitored. The results showed small changes in stability immediately, then leveled off to a smaller degree after most of the oil, salt, etc. burned off. This instability warranted that other metrology labs require gloves to be worn when handling any tubes. Future follow tests indicated that accuracy of the signal generators was more stable and required less "tweaking."

    Other tests have been conducted at the NAKA factroy near Tokyo. As a matter of fact, years ago I went on a service call for an older (very old)electron microscope that had tubes for the biasing circuit that controlled the high voltage tank. This was a medium voltage standard tube (can't remember exactly what it was) that the customer had pulled out and in repeatedly in a futile attempt to diagnose the problem himself with dirty hands. Doing this caused instability in the high voltage tank, causing beam problems.

    I think that we are splitting hairs at this point on the significance that oil/salt has on the tubes performance. Being from my background where accuracy is everything and now image is everything, little changes like this make a difference. I admittly am quite anal about this stuff.

    "To put in layman's terms, a butterfly flapping by an operating tube would have an effect on tube performance on the same order of magnitude."

    Well, that might be a slight exaggeration but I get your point. I understand your knowledge of tube technology...don't get me wrong here. I think your point is that the the effect of oil is negligable enough not to worry about. What i'm saying is that if I can extend the life and/or performance of a tube...even by a miniscule amount...I'm willing to not touch tubes with my bare hands. Admittedly, I could be splitting hairs here, but it never hurts to keep tubes as clean as possible.

    Peace
     
  13. Personally...I take the tubes out of my preamp monthly. Then I roll them in mustard and honey, then throw them in a big bucket of KFC chicken. Then lick the foodstuffs off of them.

    You two guys are way to levelheaded usually to be bickering. You both make good points.

    But handling preamp tubes is okay. It'll be fine, let it go :D
     
  14. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Here's my recipe for "8417 Grilled Chicken" (psycho can tell you about that excellent tube I'll bet):

    6) 8417 Power tubes
    16 ounces Heinz 57 sauce
    2 pounds chicken (skinned and de-boned)

    1)Fire up amplifier and play loud, greasy funk through it for 30 minutes. (Make sure speaker is connected).

    2)Lay chicken on top of hot 8417 tubes while loud, greasy funk is playing.

    3)Cover chicken with 57 sauce.

    4)Turn chicken after 5 minutes and cover with more sauce.

    5)Remove after 5 mins. Let cool. Eat while loud greasy funk is playing. Enjoy!
    :D :D :D
     
  15. Is that kind of like wrapping a steak in aluminum foil, wrapping it to your car's exhaust...and driving for like 20 minutes and stopping to eat the dead cow?

    I guess you could record the greasy funk from the 8417 chicken fire, and play it on the CD player in the car?
     
  16. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    OK, so I felt like little sarcasm.


    On a serious note: This one has RCA 8417's which I think were made by Sylvania. I think that GE trouble was why that tube wasn't used much; it was given an undeserved bad rap. It was an excellent tube and was showing the way for the future of power tubes, which never happened!
    Feel free to correct me psycho. I won't get mad!:cool:
     
  17. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Its an SG 200 PB, 200 watt mono power amp. Yea its a strange bird. I found out that it was made by CMI Electronics which was an American subsidiary of Marshall. Yes, THAT Marshall. They made some g&^%$r amps that were innovative but not successful. This one was made for PA installations. It sounds great and I use it for driving a speaker when micing my bass in the studio.
    Here's a pic:
     
  18. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Here's the business end:
     
  19. chris h

    chris h Guest

    Jun 16, 2002
    Oxford, England
    So....


    How do I replace a tube again??!!

    Some very interesting info there guys, thanks. I think it is safe to say you are both pros in this particular field! DOWN WITH GLOVES!

    The tube I replaced my sovtek with was a PM pre-amp tubes 12ax7a. Has anyone tried PM tubes? have you heard of em? the bloke said it was a top tube, and cost £10. I could list the features on the box if desired.