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ANOTHER tube thread-NOS 6550s or new

Discussion in 'Amps and Cabs [BG]' started by poorbassist15, Aug 11, 2019.

  1. As the title says, I had a tung sol go gassy in my SVT. It has a ding in the envelope, likely from where the tubes were installed and the spring retainer was allowed to slap the top of it. They test at 80% but rattle like you wouldn't believe. A tap with my index finger while holding them sounds like slapping a spring. They all appear to show marks from where they were initially installed as I'm sure the prior owner is a dunce. It has a bit of a roar/crackle at startup, probably(my guess) from one of the rest of them going bad. So, before I get bitten in the rear at a gig again, I think it's probably best I retube this thing.

    What is the cheapest NOS option? Yes I realize this is a bit of a paradox, but seeing as how golden lions are 350 a sextet that can't be too far off what actual good tubes cost.
    Failing this, what is the most reliable 6550 out there that's new? I've had poor experience with JJ, but they're so cheap I could buy several sets and sort the hyper ones out for stable ones. Looking into the glass on the groove tube spares I had, they're exactly the same plate structure as the tung sol, so I'm assuming all new sensor tubes are the same.

    Funny enough, the bottom of the barrel chinese 12ax7s I have in it(from spares, tested 98 to 102% if you can believe that) with no names have been utterly reliable, with no issues at all to report. I know TAD has got a GE 6550A reissue, but no one really seems to be familiar with these. I'm wary of China tubes as I think most of y'all probably are but if they work and don't fail, I'd be willing to try it.

    Live and learn, I suppose.
  2. Wasnex


    Dec 25, 2011

    I would stay away from the recent New Sensor designs, which include the Tung Sol and the Gold Lions...and especially the EHX. These tubes can sound nice, but I have read a lot of threads where various New Sensor KT88 and 6550 under these brands have lot's of trouble with high operating voltages. Several of the used amps I have bought had EHX 6550 and KT88, and all of them failed rather quickly or were not working when I received the amp. I have been replacing bad tubes with JJ KT88s and they have been very reliable. All the amps I have bought with JJs have been 100% reliable.

    The old Sovtek 6550WE seems to have a fairly decent reputation for reliability. Some people claim Shuguang makes a reliable 6550, and this is the the GE copy you mention. They don't seem to be widely distributed in the US but Dougs Tubes and Antique Electronic Supply Carries them under the Valve Art label. I believe the Ruby 6550A-STR is the same tube. FYI, it's not really a GE copy.

    My Skunk SVT is still running the original tubes and they may outlast me. If they don't, I'll either install JJ KT88s or make some calls about the Sovtek 6550WE versus Svetlana 6550C. I believe the Svetlana is a new design that is closely related to the Sovtek that is supposed to have extra heat dissipation fins. One problem is I have seen threads where people order Sovteks and get Svetlanas or vice versa. The Tube Store and Tubes For Amps carry both, so you might give them a call and ask if they can tell you anything about the reliability of these tubes compared to JJ 6550s and/or Valve Art 6550A.

    FYI the KT88 is rated for higher plate and screen voltage than the 6550. Per the datasheet, the plate limit for a JJ 6550 is 600V and SVTs run around 690V. The plate limit for a JJ KT88 is 800V.
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    My experience is that the real world maximum plate voltage depends quite a bit on the actual screen voltage, the numbers published are not absolute.

    The 6550's in general aren't a very quiet tube mechanically, but actually hold up quite well in this regard. My experience with 6550s is in general better than KT88's.

    You may be better off keeping the tubes you have and replacing the one bad tube with a somewhat matched replacement.
  4. Yeah I actually was looking at pictures of the two, it's not really a copy, but TAD claim that they're made to much tighter tolerances and with higher quality material than the run of the mill shuguang. Per a post on a dynaco forum "The KT88-STr is the only KT88 on market with consistently low Ig1 < 200nA at 500V Ua and Ug2 operating." It appears they've done their homework, at least. They're rated at 680v(the 6550, not the kt88), which is more than the actual GE. EDIT: matter of fact, looking at the two datasheets, they're rated exactly the same as the GEs in every other category. Did they really get it that close, or is this marketing gibberish? I smell copy-paste here.
    Last edited: Aug 12, 2019
  5. I have some spare groove tubes I'm running in it to get me through the next two weeks' shows and then I'll at least have some downtime to match a set better than just sticking spares in. My boss tested them when he was doing some accounting today and said they were rock solid at 80%.
    Wasnex likes this.
  6. The Bugera 6550B are rebadged Shuguang.
    Wasnex likes this.
  7. Wasnex


    Dec 25, 2011
    I agree the screen voltage is a significant factor. The SVTs run the screens around 350V and the JJ data sheet limit is 400V. Another factor is the bias is set relatively cold in SVTs, which I believe helps improve reliability when your busting the plate voltage limit. Still it seems a fair number of people are having trouble keeping 6550s in their SVTs.

    Some other factors: The screen voltage limit for JJ KT88 is listed at 600V versus 400V for the 6550. KT88 Plate dissipation is 42W versus 35W for 6550. Screen dissipation is 8W versus 6W for 6550. I am sure I am missing something, but it just seems the KT88 would be running way more conservatively and quite a few people have reported good results running KT88s in SVTs.

    If the five tubes are good, buying a matched trio of tubes with similar ratings to the old tubes would seem to be an easy solution for someone who lacks test equipment and basket of tubes to go through in order to find one that matches. I have used up most of my used good pulls, so I will need to buy a few matched trios and quads, to replenish the pile.
  8. Through further reading it seems most tube sellers claim the tung sol is actually the best new sensor made, so there that is, I suppose.

    The JJs seem to be just as expensive but with a burn in procedure from one of the popular vendors might be the best option, they seem to test very well on all of the videos I've seen of them actually put in amps and measured. And, the tung sol and jj both tested better than the real deal vintage stuff, but that could be down to age as well. I'm really wary of jj as I had a brand new one redplate in my pignose when the bias was okay, and another destroyed the power section of my fender (excluding the transformer). They sound great though, that pignose is the single best sounding amp I own and I really wish I could find someone to make me a 3 or 400 watt version.
  9. Wasnex


    Dec 25, 2011

    What do you mean by the bias was okay? The bias needs to be set by the amount of current passing through the tubes rather than by a bias voltage applied to the control grids. If you intend to set the bias to a certain voltage, you need tubes that are graded to work in the amp.

    My only experience with JJ 6550s is in my Orange AD200B which I believe comes stock with them. I bought the amp used a few years back and have not opened it up yet. It sounds great and seems to make good power. I found a thread that listed the amps operating plate voltage as 675V and the screen voltage as 385V, so the plates are bit lower than the typical SVT and the screens a bit higher. I believe some of the current SVTs also come stock with JJ 6550s.

    If I were buying JJs I would get them from Eurotubes. If I was considering Tung Sols I would call TC Tubes. They sell Tung Sols and also Sovtek 6550WE, so you could tell them you amps operating voltage and ask their opinion on which tube is likely to be more reliable. I haven't bought any output tubes from TC yet, but I have bought quite a few NOS small signal tubes from them and been very pleased with their service. They advertise the ability to match tubes at your amps actual operating voltages, which is both good and unusual.

    There are some old threads warning about using the Tung Sol 6550s in amps with high plate voltage, but you are likely to find warning threads about any tube. @coreyfyfe mentioned that he had a set on the shelf that he was planning on putting in an SVT. I don't know if he ever did.
  10. It was where it should have been for a 6l6, amp is fixed bias, I have to actually find the page of notes the tech wrote for anything else lol.

    I'll probably go with JJ KT88s if I have to but I think I'll just run these til they toast themselves. Thanks for the clarification, everyone.
  11. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    I did, they’ve performed well in the limited use I’ve given them. I ordered my set from TC tubes and mentioned in my order they were for an SVT so they were tested at appropriate voltages. The set they replaced were a well worn sextet of winged C (one started getting noisy), and oddly enough when I went to set the bias they were almost perfectly in range. I’ve had mixed results with current NS stuff, the Gold Lions I’ve tried have not been up to snuff, but only positive experiences so far with a variety of TS and Mullard branded tubes. Have also had great results with rebranded Chinese production from Ruby and TAD so those may be worth investigating.
    Wasnex likes this.
  12. SteveIII


    Jul 11, 2019
    The guy from lenardaudio suggests that screen voltages be more than 380 volts for full power but that over 400 volts the tubes will die quickly if driven to full power. I don't know if he is as smart as @agedhorse but it backs up what he said. And what bass player uses the full power of their amps right?:)
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Higher screen voltage can affect tone and dynamic feel too. It's just another tradeoffs.
    Wasnex likes this.
  14. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    I had a TungSol reissue 6550 go gassy in my SVT. Bought a matched replacement... and another one went gassy. The second one took out a screen resistor in the process. Just saying....

    I replaced the TungSols with JJ KT88s from Eurotubes, haven't had any problems, but I rarely get to use that monster so I'm not sure that's very significant.
  15. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    My experience with 6550's is very limited because the HSVT-CL I got in 13 is the only amp I've had that uses them, but after 6 years of moderate usage, the JJ's in it are holding up well and working fine. I've also used rental SVT's that come with the cheapo EHX's and they sound fine to me as well. Honestly, I'm way less concerned with the power tubes than I am V1 in the preamp, which is the only tube I ever notice any tonal change in any amp. And after some experimentation with a new Tung Sol and a couple NOS tubes that represent the end of my NOS tube collection, I put the JJ back in. Everything else was too bright, but the JJ and Ruby I tried in it made it sound just like my 69 with all NOS tubes and an Amperex 12DW7 in V1.
    rodl2005 and jdubbass38 like this.
  16. jdubbass38


    Mar 20, 2009
    Shoot, I wish this thread was started before I re-tube my svt2pro! This would of been helpful to see what everyone likes to run. I ended up putting the EHX 6550s (learning they are the cheep-o’s) in it and it seems to run fine so far. My other svt2pro is still running the stock Sovtek 6550s in it. It would be interesting to run them side by side to see if I can tell any tone difference. Only thing I’ve noticed so far is the one with the new EHX 6550s seems to be slightly louder (makes sense with brand new tubes) but it also runs a lot hotter. Not sure if it’s because of new tubes vs old or it being EHX 6550s or something else going on. Both fans are running so it’s not that... but the svt2pro with the EHX 6550s is hot to the touch (burn your fingers hot) compared to the other being hot but you can rest your had on the metal enclosure. Tech says both are running to spec so I guess I’ll see. The amp I re-tubed had 5 sovtek 6550s and 1 ruby 6550 come out.
    rodl2005 and JimmyM like this.


    Dec 21, 2007
    Cowtown, USA
    Glad to see the Heritage 50th Anniversary SVT are using JJ’s for tubes (with cool Ampeg logos embossed on them!).
    My only experience with JJ’s are the KT88s I’ve had in my Trace V6 for over a year and sound great.
    Wasnex and JimmyM like this.
  18. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Hmmm...I always thought EHX and Sovtek were the same tubes. I guess they're not. Same price, though :D

    BTW, poorbassist, The Tube Store has some GE's in stock for $200 per tube if you want to go NOS. That's only $1200 to do an SVT.

    jdubbass38 and Wasnex like this.
  19. jdubbass38


    Mar 20, 2009
    I could see that conversation going over well with the wife, $1200 on tubes babe... probably be my last! lol.

    I’ll stick with what I got!
    JimmyM likes this.
  20. Wasnex


    Dec 25, 2011
    upload_2019-8-13_21-53-40. upload_2019-8-13_21-54-7.

    The guts look pretty similar, but the glass envelop is obviously different. From the reading I have done, the Sovteks have a reputation for taking pounding and the EHX have a reputation for high infant mortality rates in circuits that run high voltage.

    Just because two tubes look identical does not mean they are made with the same metals and coatings.

    I am not certain, but I suspect EHX KT88 are the same construction as their 6550s.
    I have received amps with both EHX KT88 and 6550, and the 6550s failed first. All of the 6550s lost the ability to hold bias and the current ran away. The KT88s had a wide variety of failure modes, shorts, low current, no current, etc. 100% failure of EHX KT88 and 6550, but all came to me in used amps.

    The provenance and history of these tubes was unknown, but I have bought lot's of amps still running OEM tubes from the 90s and they were way more reliable than the EHX tubes. Most of them got noisy are started sounding bad so I replaced them...almost zero catastrophic failures. The EHX tubes all appeared relatively new, and some came as OEM in almost new used amps I bought. My opinion is they are junk.
    jdubbass38 and JimmyM like this.

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