One power tube is red-plating in my 6505...help?

Discussion in 'Gear & Equipment' started by KailM, Jan 2, 2018.

  1. KailM

    KailM SS.org Regular

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    Hey folks, I thought I'd run this past you all since I've never experienced red-plating before. I was playing today when my amp made a moderate "pop" sound but didn't die or anything. The tone still sounded pretty normal for the most part; though I've been thinking lately that it seems like I haven't had as much low-end in my tone. That's hard to tell because I've also had a head cold which always seems to affect my hearing.

    Anyway, I stopped playing and looked around the back and saw that one of the power tubes was glowing pretty brightly on the plate, and I began to hear a low pitched hum which was increasing in volume. I immediately powered it down at that point. Obviously, that tube needs to be replaced, but before I order a new quad I was wondering if there's anything else I can try. I know power tubes need to be matched, and I have spares, but not a matched-quad worth of spares. Since the 6505 is biased pretty cold, could I get away with running another power tube that might not match the others perfectly? They would all be JJs, if that makes any difference. They probably aren't all that different from each other, in fact. Thanks for your $.02
     
  2. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    Yeah you can get away with it. Ideally you’d replace the full quad, but another acceptable solution is to replace either the inner pair or outer pair, depending on which one failed.
     
  3. KailM

    KailM SS.org Regular

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    Thanks man! I did pull the two innermost tubes last night (one of which was the red-plating tube) and set the impedance to 8ohms (running it at 60 watts), and the amp functioned normally with no red-plating. However, the amp tone is still not right. It has plenty of mids, treble, gain, and volume, but there is not enough/barely any low end.

    Thinking it might have just been my ears (head cold causes hearing issues for me), I hooked up my 6505+ 112 head; which is also 60 watts, and it blows the other amp away. So it's not my ears -- the 6505 mk 1 is not working properly, because normally it has even a touch more low end than the 6505+ 112 head.

    So I think perhaps the whole quad of power tubes is on the way out -- loss of low end has always been the first sign that they need changing. Supposedly they were new last winter, right before I bought the amp. But that might not be true, and in any case, I have played the amp A LOT over the last year, and pretty loud most of the time.

    The tubes in there now are stamped with a "20" (bias point reading?) from the dealer; my extra 6l6 tubes are also marked with a "20," although from a different dealer. Would it be safe to assume that they all match, due to having that number? I really just want to put one of my spares in that position to rule out any other problems with that slot. If another tube red-plates in that slot, then I'll know I've got to tear it down and investigate.
     
  4. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    Yeah dude it’ll be fine. Peavey cold biased these amps because they knew tubes are all over the map now a days. It is less expensive to just bias cold vs making individual bias points and hoping the amp owners know how to do it. Since most of the mojo comes from the pre amp with these, the cold bias isn’t a huge deal and helps to extend tube life a little, and the bonus is it allows you to replace a single tube in a pinch.
    But if it was from a quad; if one is gone the rest are probably coming soon. A year of heavy use is all you get out of tubes anyways.
     
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  5. BadSeed

    BadSeed SS.org Regular

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    Sounds like you could really benefit from a new set of pwer tubes. If you're losing your low end and 1 of your tubes gave out, the other ones probably aren't too far behind.

    As for checking the slot that the one red plated in, you could just move your 2 good power tubes from the outside slot to the inside slots. If they run fine like this, the amp is ok. Either way, new power tubes would be my vote for sure.

    Also as far as Peavey's cold bias, they designed the amp this way to induce crossover distortion, which is part of the sound of these amps. Having done the Bias mod, it warms the amp up a bit but takes away some of the hard edge of the palm mutes that these amps are known for. Pretty much any 6l6 will be fine, none are rated hot enough to cause issues with the amp being biased so cold.
     
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  6. KailM

    KailM SS.org Regular

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    Thanks for the advice fellas!

    Turns out it was just the tubes -- they're shot. (Kinda weird how fast they went -- just a few weeks ago the amp sounded amazing, and now they sound terrible; I've never had power tubes degrade this quickly. Usually they very slowly degrade over about a year's time and I change them; only noticing the degradation when I hear how good the new ones sound.)

    Just now I put two old tubes that were matched in the two middle positions (one of which was the red-plating position) and they not only didn't red-plate; they sounded great! I played for about 10 minutes with the volume at "3." It's not quite as loud there as it is with 4 tubes, but it's plenty loud and brutal AF. I almost wonder if I really need to run 4 tubes...

    Anyhow, the tubes I put in are definitely well-used, but obviously in much better shape than the ones I took out. A new quad shall be ordered...:)

    Has anyone ever used Tung Sol 6L6s in a 6505? I've only ever used JJs and think they're great. But I'd consider trying something new.
     
  7. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    Never used tung sols for power tubes, but I have a bunch of their pre amp tubes and have always been happy with them. I have always used Mesa, JJ, and Svetlana for power tubes. Trying new power tubes and combinations of different makes and style pre amp tubes is always awesome
     
  8. BadSeed

    BadSeed SS.org Regular

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    I'd look up a few different 6l6 brands and see what suits your taste. Each tube imparts a different flavor. I've currently got Winged C's in my 6505+ and EVh 5150, and they sound excellent. I've always had good results with Ruby 6l6 in the 5150 series too. JJ's seem to be a little darker, smoother. Haven't heard much about EH or Tung Sol 6l6's to be honest, but that doesn't mean they're bad.
     
  9. Shask

    Shask SS.org Regular

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    Yeah, you can just replace that one tube for now. I have a Marshall clone that has been running with 1 odd tube for a few years, lol. It doesn't even look the same as the others, even though it is the same type.

    I used to use JJ, but think I used Ruby the last time I put new power tubes in an amp. I used TAD before that also. It is hard for me to tell the difference between power tube brands.
     
  10. vick1000

    vick1000 SS.org Regular

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    Tube matching is a myth. It's important to eliminate certain distortion characteristics, so matching is very important in hi-fi units and such, not as big a deal in guitar amps. As long as all tubes are within spec, you are safe to use the amp. Some people even prefer the harmonic distortion of unmatched tubes. However, having a well matched set of the right type of tube, in a well biased amp, can make some amps seem to come alive with harmonic content.

    Whatever you choose, get your tubes from a reputable source that does at least a 24hr testing and burn-in before matching. The best tubes I have used in the 5150 series is the Sovtek WXT+, and they are some of the most affordable as well. You might as well swap preamp tubes as well, if you can afford it.
     
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  11. KailM

    KailM SS.org Regular

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    Bumping my thread because I'm still not sure what tubes to order, lol. I've been playing the head with just two tubes for the last week with the impedence cut in half. At first, I thought it was fine, but after a while I realized it just doesn't have the low-end I like. Compared with my 6505+ 112 head (60 watts) it just doesn't have the low end balls -- and I even swapped the tubes from my 112 into the 6505 and it still lacks in low-end/low mids content. For whatever reason, though I can run the big head with just two power tubes and cut the impedance, it really doesn't sound equal to my dedicated 60-watt head.

    I finally tried putting two of the worn-out tubes back in for a full quad of 6L6s and the low-end came roaring back to life -- albeit not at the same level as it was previously (the tubes are still on their way out/not optimal.) Like you said, the tubes aren't necessarily matched -- yet it sounds remarkably good and didn't seem to suffer from the mismatch (it's possible that the tubes ARE matched, but they definitely came from different stores. So, in a nutshell, I've gotta run this head at the full 120 watts for it to sound right.

    I've been perusing threads about power tubes all over the web for a while now, and the Sovtek WXT+ like you recommended has come up pretty often as highly-recommended. My only experience has been with JJs and cheap Rubies (Shuguang), and generally the JJs sound amazing to me when they're fresh -- far, far better than the Rubys. Despite the 6505/5150 series being primarily preamp-driven tone, the power tubes DO make a noticeable difference.

    If money was no object, I'd buy several quads and ultimately find what I like best -- but experimentation with a full quad is kind of expensive on my budget. If I purchase a quad of non-JJs, and don't like what I hear -- well, I'm probably stuck with it for the next year, as I can't keep throwing money at new tubes. If you can, can you describe the difference between those Sovteks and JJs?
     
  12. Shask

    Shask SS.org Regular

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    Yeah, I hated the 5150 for a couple of years because I ran mine at half power. Pulling 2 tubes makes it have less bass, and the bass it has is all muddy and sludgy. It definitely needs all the power tubes to sound right.

    Usually JJ tubes are darker than Sovtek. JJ can be good in a 5150 to help tame the high end fizz.
     
  13. vick1000

    vick1000 SS.org Regular

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    IMO the WXT+ are more dynamic and brighter than the JJ 6L6, you will get more output across the spectrum with Sovteks, and more "tube" feel when you crank the amp. They are the best tubes for the money in my experience, at least for high gain metal tones. They really give you more to cut with than other 6L6s in a 5150 IMO.
     
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  14. TheWarAgainstTime

    TheWarAgainstTime "TWAT" for short

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    Second. I love the WXT+ tubes I have in my 5153 50w. Much more clarity and defined bottom end punch than the stock JJ's. Mesa 6l6 are good too, pretty sure those are rebranded WXT non-plus tubes.
     
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  15. KailM

    KailM SS.org Regular

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    Well, that settles it -- I think I'll try some Sovteks. They're about the same price as JJs anyway.

    I'd love to try some Winged C's or NOS Sylvanias but have you guys seen the prices on those these days? Outrageous...
     
  16. vick1000

    vick1000 SS.org Regular

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    Don't believe the hype of NOS, they are more trouble than they are worth, due to all the scammers out there, and they don't sound much better in modern circuits, especially high gain amps. Winged =C= were nothing special in 6L6 flavor, it was their EL34 that stood out. If you want something more outstanding for a 5150, try Tung Sol's 7581a. Just be sure you get your tubes from a reputable dealer that does a 24hr+ burn in.
     
  17. KailM

    KailM SS.org Regular

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    Probably a wise policy, especially regarding power tubes that only last a year or so anyway. FWIW brand new JJ 6L6s have always blown me away in my 6505s -- but I've never been able to A/B them with anything to know if I'm missing anything.

    I have one NOS 12AT7 that sounds quite clear, but I only like it in my Classic 30.

    I like 5751s in my 6505s for V1 and the PI -- always wanted to try a JAN 5751 but every time I look at their price I'm like "damn, I could buy 4 JJs or Tung Sols for that." At least preamp tubes last a long time though...
     

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