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Tubes and the Barely Capable

Discussion in 'Amps and Cabs [BG]' started by Folmeister, Jan 27, 2005.


  1. Folmeister

    Folmeister Knowledge is Good - Emile Faber Supporting Member

    May 7, 2003
    Tomball, Texas
    Hi, Gang:
    Well, I got new JJ tubes for my Buster 200 1X15 combo and managed to get the amp section out and replace the tubes. Then I managed to get the whole thing back together (if you have not picked up on the fact that I am a tard when it comes to this stuff, you will soon). I fired it up and it sounded a lot better. BUT, one of the 6L6s is not glowing. AND, there seems to be a kind of blooming metallic sound behind the signal. It's in the background so it's not that bad. I need advice about what all this means before I dump this whole thing off an a tech for $$$. Anyone?
     
  2. Pickebass

    Pickebass Supporting Member

    Jul 12, 2004
    San Antonio, TX
    Is the tube purple? If it is you've got another problem. Since it is working it could simply be a bad tube. Try swapping the tubes you have and putting another in that location. If the same tube lights up, it's something in the amp socket. If another tube lights up in the space it's the tube. Did all of your old tubes work before you removed them??
     
  3. Folmeister

    Folmeister Knowledge is Good - Emile Faber Supporting Member

    May 7, 2003
    Tomball, Texas
    I'll start there. I just dread taking the thing apart again. It does not glow purple. It just does not glow.
     
  4. Bongolation

    Bongolation

    Nov 9, 2001
    California
    No Bogus Endorsements
    I can think of several possibilities, none of them good.

    I'm assuming you replaced these tubes and did not rebias them? That can cause damage, or this could be a couple of other things.

    Replacing power tubes is not considered user maintenance except in amps with external bias adjustment.

    Replace the original tubes and see if that makes any difference.

    If you still have a problem, definitely consult a tech.

    Good luck!
     
  5. Bongolation

    Bongolation

    Nov 9, 2001
    California
    No Bogus Endorsements
    Purple glow in a power tube is not abnormal. What is abnormal is that you have two nominally identical power tubes working together that do not look the same, i.e., one's glowing and the other isn't. Whatever these tubes should look like, glowing or not, they should look like each other.
     
  6. Rockbobmel

    Rockbobmel Supporting Member

    Also, did you work the tubes into the sockets? What I mean is plugging them in and wiggling them out and back in a few times. Chances are that the shape of the old pins and the new are different. This can make for bad contact. My2 cents.
     
  7. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    There are several possibilties. The first (and most likely) is probably a bad tube. Tubes go bad all the time in shipping and such, and when you first plug them in, but unfortunately the manufacturers aren't going to give you the benefit of the doubt that it was "their" fault instead of yours. So, my first suggestion would be either a tube tester, or replacing all the output tubes with a known good reference set, for testing purposes. If you can establish that the amp itself is working okay, that's a good first step.

    Another possibility though, is that the amp isn't really working. You might have a flaky tube socket, or a bad resistor or capacitor or something. So another approach would be to take your new JJ's and put them into a different amp, one you know for sure is working correctly.

    The third issue has to do with "biasing", or more simply in this case probably, the "matching" of the tubes. If one of your tubes isn't glowing "at all", that means the filament probably isn't lighting, which to me would suggest either a bad tube or a bad socket. But, it's possible there may be a subtle glow and you're just not seeing it? Or, the glow may have a slightly different color/hue because the bias point is way off (or there's no bias at all). When you're putting a duet or quad of new tubes in an amp, it's important not only to "match" the tubes, but also to tweak them in-circuit so they're matched operationally. Both grids (or each push-pull pair) want to see approximately the same steady-state bias. If you don't know about biasing tube output stages, I'd suggest taking your amp to a decent tech, it'll be well worth the hundred bucks. Otherwise, you can invest in a digital multimeter and a bias gadget, if you're willing to spend the time and energy learning how to do it yourself. In the latter case, we can help you, but in the former case you're at the mercy of your tech. :)
     
  8. Folmeister

    Folmeister Knowledge is Good - Emile Faber Supporting Member

    May 7, 2003
    Tomball, Texas
    Thank you all for your recommendations! I pulled the questionable tube and it had a white haze to the top of the bottle that the others did not. I took it out and put another in the same socket. It worked fine. I got my glow and I let it sit for an hour or so with no ill-effects. I fear I got a bad tube, or I did something I should not have to it. I will play with the amp for a while and monitor all new tubes. I think I got lucky this time!
     
  9. ElephantTalk

    ElephantTalk

    Jan 20, 2005
    Indy
    My Buster keeps popping fuses.
    Granted I've got fuse that's rated at a 1/4 amp less than the one that is supposed to be in there, but no one around here has the 6.25A fuses.
     
  10. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA

    Excellent! JJ's are nice sounding tubes IMO, and I haven't had too many quality control problems with them. Maybe you got a bad tube due to shipping or something, that happens every once in a while. If your new tube is working okay, and your amp sounds okay, you're probably good to go. If we were going to be sticklers about it, I'd probably recommend a bias check, but who knows, your amp may be very tolerant that way. Some amps don't even have a bias control. But if there's a little knob somewhere on the backpanel or the chassis that says "bias" or "output balance", I'd probably take it to a tech and have him tweak it to perfection (which you can probably do yourself, if you're okay with that kind of thing), basically just turn your volume control all the way down, and adjust the bias knob for minimal hum. If there's an additional knob called "hum balance", then after you set the bias control, turn the volumes all the way up (without your instrument plugged in) and adjust the hum balance for minimum hum at full volume. That's kind of the "poor man's method" for adjusting bias and filament balance, and it works fine. But, if your amp sounds okay to begin with, with the new tubes and all, you're probably good to go, and the bias adjustment probably isn't a critical issue. You can always play the amp for a while and see what happens. If a tube blows up, you'll know it soon enough. :D
     
  11. Folmeister

    Folmeister Knowledge is Good - Emile Faber Supporting Member

    May 7, 2003
    Tomball, Texas
    I had a hard time finding them also, but there are independent electronic stores that stock or can order them. Try the Internet? Don't go to Radio Shack!
     
  12. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    6.5 will work fine, and 7.0 will probably work fine too. Generally if an amp like that fails, it won't be a matter of a quarter amp. Feel free to substitute the "nearest available value". Except if it gets way out of range, like you don't want to go to 20 amps. But an 8 amp fuse (which is pretty standard) would probably adequately protect your amp. In about 99.99% of the cases. It's the other 0.01% of the time when you really need the 6.5 (or 6.25, or whatever). And my feeling is, based on 40 years of experience with tube amps, that it ain't gonna make a difference if it's six and a quarter or six and a half, if your amp fries with that kind of a fuse then you have a lot more problems than just how many amps you're running through the AC. Just a thought, for your consideration. :)
     
  13. Here's your problem:

    The tube has cracked and lost vaccum. It's trash. The white haze is the getter completely oxidizing. You either got a bad tube or cracked the envelope when you installed them. Any REAL tech with minimal experience could have told you that right away.

    A situation like this underscores the importance of having a relationship with a real amp repair tech. Ignore the advice to not 'be a tech's mercy.' Anyone who implies that service technicians are somehow dishonest is a bigger fraud than Aspen Pittman. Trust me, there's no money in fixing amps and most guys who do it do it for the love. If you want to waste your money on a bias gadget and some how-to book by a self-proclaimed tube guru, that's your prerogative, but if take that same amount of money and spend it on a tech and put a little time into picking his brain, you'll end up being able to care for your amp much better.
     
  14. Rockbobmel

    Rockbobmel Supporting Member

    Good to hear from you. I also have learned that because techs have a lot of understanding of the science, they like it more if you let THEM explain what's wrong and go with THEIR recommendations. They are not like car mechanics.