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New to tube amps - questions

Discussion in 'Amps and Cabs [BG]' started by MichiBass, Oct 24, 2013.

  1. Hey,

    I just bought a great 70ies tube bass amp, a Solton BV 60. I already had a gig with it, and I love it, but now I got home and I started to restore it a bit, clean it, new tubes, etc.

    Specs: I guess 60W full tube amp, with two 6L6 tubes (I have Mesa Boogie 440 STR, which I read are top notch tubes), and two 12AX7 tubes (I have one Mesa 7025 STR and one Ultron ECC83). I also have a ECF 801 tube I found at my place, and a Sovtek 7025/42AX7WA/1002 tube from a friend's keyboard amp. I don't know about if the any of the tubes I have are new or much used.

    My amps is similar to this one: http://www.albertkreuzer.com/bv60.htm (not the housing, but the inside)

    Questions are:

    1. Shouldn't the preamp tubes be matched? I read power tubes should be matched. I have different ones.
    2. Is the ECF 801 tube I have a 12AX7?
    3. Can I just try my preamp tubes out, to see which I like the most?
    4. Are the preamp tubes I have good? Which are the best?
    5. The power tubes are great, but at volume 6/10 I already have distortion, which I don't want to... Is this because of the too high gain power tubes? Or because of the "wrong" preamp tubes? Which tubes have "lower gain" so that I don't get into distortion?
    6. Both tube sections have a pot on the inside. Is this for biasing the tubes? What is biasing? Can I do it myself?
    7. I have three outputs for cabinets: 16, 8 and 5 ohm. Yes, 5 ohm??? Can I plug a 4 ohm speaker there?
    8. Will an 4 ohm cab sound louder then a 8 ohm cab plugged to this amp? I know this is the case with solid state amps.

    Thanks a lot.

    And any tube recommendations are welcome.

  2. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    1. No. Preamp tubes don't have to be matched, either to each other or with balanced halves (many preamp tubes are dual triodes, essentially two tube circuits in one tube). Preamp tubes are cathode biased and will adjust to the circuit and as such, swapping them into a single circuit highlights the differences in how they reproduce sound well. Power tubes in a push-pull setup should be matched specwise, not necessarily same brand as long as they have matching specs you should be good.

    2. No. The pinout is different.

    3. Yes. Just don't use the ECF801.

    4. Best is subjective. What sounds good is what's best. The mesa str tubes are custom spec'd (sometimes) and tested Chinese or Russian manufacture. Many people don't like them because they're basically overpriced versions of other readily available tubes.

    5. You're probably running into headroom issues. It's a 60 watt amp, I wouldn't expect it to be super loud without some distortion. Be sure it's been checked by a tech, had a cap job, is up to spec at all points in the circuit. Could be the tubes, could be that some component is aging.

    6. You can do it yourself and there are a lot of tutorials online. I'd say you should bring it to a tech and get it cleaned up and have them bias the amp if you don't have the experience and knowledge to do it now. Be cautious as the power supply caps on an amp like this can store upwards of 500 volts. Not something to be playing around with if you don't know what you're doing.

    7. Yes. That's closest to matched. With a tube amp, going lower than rated (plugging a 4 ohm cabinet into the 5 ohm output tap) is generally safer long term than higher than rated (8 ohm cabinet into the 5 ohm output tap). Ideal would be a matched load.

    8. With the output transformer it should push the same wattage into either cab when using the proper impedance setting.
  3. bkbirge


    Jun 25, 2000
    Houston, TX
    Endorsing Artist: Steak n Shake
    Tube amp bias:

    You don't have to match preamp tubes usually, this is where most people swap things in and out for flavor. For example a 12au7 is often substituted for a 12ax7 in order to lower the preamp gain (of course if you are swapping different TYPES of tubes like that then you might need to change out a bias resistor or 2). Normally people swap like tubes, for example an RCA 12ax7 might replace a TungSol 12ax7 for some perceived sound benefit (or detriment!).

    Best tubes? That's a religious discussion.
  4. 1) No preamp tubes do not need to be matched.
    2) Are you sure that is not ECC801 (12AT7).
    3) Yes that is called "tube rolling" and many do just that.
    4) Your Ultron is probably the "best" being old world production.
    5) Distortion at 6/10 is very common, designed that way so it sounds louder faster to make the customer think the amp is more capable than it really is.
    6) It could be bias adjustment and if you do have separate bias for each output tube you really don't need matched output tubes. With some training and/or special tools you can do it yourself.
    7) Yes you could use a 4 ohm speaker with the 5 ohm tap. Tubes are more forgiving of lower impedance than higher impedance miss-match.
    8) No. Tube amps or any amp with an output transformer will put out the same power at any of the rated loads.
  5. E indicates a 6.3V heater.
    C is a triode
    F is a small signal pentode

    Thus an ECF801 is a 6.3V heater with a triode and a pentode sections. It is the 801st tube carrying the ECF prefix.
  6. Dang should have remembered that :cool: Maybe closer to a 7199?
  7. Beware, tube amp ownership often leads to cork sniffing...

    ah, a 1964 Telefunken... excellent year!

    ...Wait, these are not blackplates! These are FORGERIES!

    You can swap out a number of different tubes in your 12AX7 spots. I kinda like 5751's, they have 70% of the gain of a 12AX7 but have all the same other specs as a 12AX7. All others have different specs an may need different cathode resistors or bypass caps to be optimized, but pretty much you can plug in any 12A "?" 7 tube and it will work. 12AT7, 12AU7, 12AY7...

    Probalby the best bet is a 5751 with a 12AT7 in second place for swapping out for less gain.
  8. ^^.

    Yeah, not compatible with a 12A*7 anything. That would be a dual tube as well, but would be a triode and pentode in the same glass bottle. I have never seen a guitar or bass amp using an ECF801... in fact I've never seen an ECF801. (edit: for some reason there was something ringing in the back of my head about this but it was just being dumb.. I was thinking I might actually have one but it turns out I have an ECH81 in a box on my shelf.. triode + heptode!)

    An ECC801 is the "higher grade" version of the ECC81, which is the Euro label for the 12AT7. Likely it's just some funky coating on the plates or something to make it 'high grade.' I looked up the schematic and the only decent one I can find lists your two preamp tubes both as 12AX7s. The 12A*7 tubes are all technically pin-compatible but that doesn't mean they will sound worth a damn when switching things out.

    The pot by the power tubes is for biasing, yes. That means you don't technically have to have 100% matched 6L6s, but you'll want a tech to be the one turning the knob, not you, and you'll probably prefer they did it while hooked into a power soak and looking at it through an oscilloscope. The schems I found don't show your amp as using 6L6s but EL34s instead. EL34s are (according to wikipedia, ha!!) known for their higher distortion: http://en.wikipedia.org/wiki/EL34. It also doesn't show a hidden pot in the preamp. It shows bass/mid/treble, presence, and volume and that's it.

    Different versions, maybe? Is yours made with a PCB or is it point-to-point wired? I read on albertkreuzer.com that there were at least two versions with the early ones being point-to-point.
  9. Mosfed


    Apr 21, 2013
    Chamonix Mont-Blanc
    Partner - CCP Pedals
    1. Preamp tubes don't need to be matched but often if you want to see the true sonic character of a particular NOS tube,you will hear it best if you have a whole set.
    2. Totally different tube. You can't use it.
    3. Yes your ears should be the judge provided the types match
    4. No they aren't anything particularly special - pretty cheap Russian tubes
    5. It could be your preamp tubes - some 12ax7s are great in guitar amps because they crunch sooner (eg Mullards) but that isn't ideal with a bass amp. But your Sovteks aren't really like that. I think you are just seeing the limit of your amp and it's clean headroom.
    6. You can learn how to bias. It's not tough. But you need to learn. And it's only for the power tubes.
    7. Yup 4ohm into 5 should work.
    8. Just match the impedance as best you can and it will sound best.
  10. Thanks for all the replies, helped a lot!

    Which are the best "selling" or "popular" or "most used" (12AX7 AND 6L6/EL34) tubes in bass amps?
  11. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    My favorite 12AX7 is a 5751. ;)
    I use a set of RCA blackplates in my Kern 12AX7 tube pre and it kills any 12AX7 I've ever tried.

    My next favorite 12AX7 is a 12AU7.
    Particularly the GE grey plate versions. They're 99% of the way to the RCA's at a fraction of the cost.

    Also don't always believe the hype about tube brands. Fer instance I have a number of Mullard tubes of various types and I almost always find something I like the sound of better.

    If you're new to tube amps, why not start with looking at current production run stuff and get a feel for it before heading into esoteric territory?
  12. Also keep in mind that many "brands" of tubes are simply rebranded tubes of a completely different make. There are a bazillion makes out there but there were only so many factories - and today there are (by my last count) between 4-6 worldwide.

    I second this. It's cheaper, unless you can find stuff like I do - estate sales and warehouse sales and crazy out-of-the-way garage sales and whatnot. A lot of these old guys just want to get rid of useless junk - I have a lot of NOS Tung-Sol and RCA tubes that I got this way. Save Ebay for a last resort for when you absolutely cannot find a particular tube.

    For instance, just today I got 3 6SL7GT tubes - two Tung-Sol and one Westinghouse (not sure who REALLY made this one), 1 RCA 5U4 rectifier tube, 1 RCA 12BA7 heptode mixer tube, 1 Honeywell 5963 (12AU7-alike) and 1 black-plate GE 12AY7, all with original boxes (cept the 5963 which came in a Mullard 12AT7 box), all NOS, none ever used... for the grand total of $10 USD cash monies. It pays to hit up "warehouse sales."

    Also, I flew by a neighborhood estate sale that happened to have an old Zenith phonograph player. I didn't buy it, though they offered it to me for $30. I looked inside and saw it had a used RCA black-plate 12AX7 in it, probably original equipment. Old people didn't abuse their record players like we abuse our amps, so it probably would have been worth it just for that tube, never mind the half dozen other tubes in it. That's another source.. don't overlook old gear!
  13. will33


    May 22, 2006
    I have nothing to add to this thread, other than to say it's super cool and you have a collection of some of the best brains on talkbass helping you out here.

    That is all...
  14. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Probably the Shuguang ones, since everyone and their dog rebrands them, and they find their way into a lot of new amps as standard loading.
  15. Are they on thomann?
  16. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma

    All of the TAD products are rebranded tubes manufactured by one of the chinese or russian companies. Their "select" 12AX7 is just a shuguang 12AX7 with a custom set of specs/testing parameters.

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