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How to swap tubes in a tube amp to increase gain and easier push it into overdrive?

Discussion in 'Amps and Cabs [BG]' started by NoiseNinja, Mar 31, 2017.

  1. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    Researching a bit on the topic, though without understanding much of the technicalities, it seems that changing tubes should be able to result in both getting slightly more watts out of a tube amp, also changing it's tone notable as well as some tubes are are claimed to be easier to push into overdrive territory.

    I also picked up that the max output of the amp will be determined by the output transformer and that changing to different tubes will require a bias adjustment of the amp according to the tubes you use.

    Honestly I don't know what much of this means.

    The specific amp in question is a Dynacord Bass King all tube amp that is rated 50W utilizing 1 X ECC83 type tube in each of the 3 input stages, where I in reality only use one, the instrument input, and 2 X EL34 type tubes in the poweramp stage.

    Also I should add that as something unusual of amps from this era, the amp was produced in '63/'64, it both has an input gain control and a master volume.

    Now say I wanted to try to push the most watts out of it, which tubes might I then try using, and would it need any form of adjustments and/or surgeries to be able to utilize these new tubes/extra watts gained?

    Also say I would want to attempt to push it into overdrive, as it seems to keep amazingly clean all through it's output spectra as it is now, even with input gain set at max, which I use as default setting, which tubes could I eventual try to swap with what kind of tubes to possible achieve this, and again would such a change require any other changes to the amp than just swapping the tubes?

    To be perfectly honest I haven't looked into which tubes are used in my amp currently, as they had just been replaced with new ones before I received it, and I can't easily find out as the amp at the moment is located at our rehearsal place.

    But if I interpret the information the seller send with the amp, the tubes could very well be respectively JJ ECC83S/12AX7, 7025 tubes in the preamp stage and JJ EL34/6CA7 tubes in the poweramp stage, not entirely sure if this in fact is correct though, and, if it is, what that would mean and if those are good tubes and not least good tubes for what I had in mind.
  2. 5544


    Dec 1, 2015
    Does your amp have a effects loop? Skip to 2:40 and start watching.

  3. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    I could be wrong, but as far as I know none old tube amps produced in '63/'64 had that.

    Mine doesn't at least.
    Mvilmany likes this.
  4. More to the point you are not going get a lot more power out of your amp with new tubes without doing a lot more than just the tubes. It just ain't gonna happen.
    In general terms to get a clean tone run your master high and your gain low. To get distortion run your gain high and lower your master.
    The reality is its a 50 watt amp that will barely compete with a moderately loud drummer. About the same as a Bassman of the same year. To get the most volume add more speakers and especially more efficient speakers. Your best bet would be if it will run at 4 ohms to get two 215 JBL D-140 cabs that are 8 ohms each. That's what we all used to get the most volume out of a 50 watt amp tube back in the day. Or 2 of the biggest, baddest, best, high efficiency 8 Ohm cabs you can afford.
    Fuzzonaut and NoiseNinja like this.
  5. The effects loop has nothing to do with answering your questions. That was a little bit out of left field.

    There are tube substitutions you can make in the preamp tubes to get more clean headroom as 12ax7's run hotter than a tube like a 12au7. 12ax7's and ecc83's are interchangeable.

    Edit, also KT77's can be used as a substitute for el34's in some or even most amps but I wouldn't do it with consulting someone familiar with that particular amp.
    Also, I believe there is a club here for these amps which are common on your side of the pond. Do some searching you'll find it. They should be able to help you.
    Last edited: Apr 1, 2017
    NoiseNinja likes this.
  6. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    I actually started out, when first switching from guitar to bass, on a later version of the Bass King called Bass King T that had something as odd as a solid state preamp stage and a tube driven poweramp, also 50 W, and actually that was loud enough for me in a moderately loud power trio noise rock outfit.

    Back then I ran it with 1 15" at 8 Ohm and 2 15" at 4 Ohm, if I remember correctly, as that was the two speaker outputs it had.

    Also gigged with it miked up or through DI, and with monitor support, even a couple of times at some open air festivals on fairly large stages without problems, or small venues without any form for backup.

    Anyway the way I use it now I run it along side my Trace Elliot GP75SM 130W 15" solid state combo.

    I place another small 15" 8 Ohm cab on top of my solid state Trace combo, then my 50W Bass King tube head on top of that, and run it via the tuner out output from my Trace (which happens to be preamp, pre EQ, at instrument level and impedance).

    At the moment in between the tuner out of my Trace and my tube heads instrument input I run first a Joyo Orange Juice, which is an analog pedal that is supposed to emulate how an Orange guitar amp acts, and is capable of a great kind of gritty grindy type of overdrive without any low end loss, and then into a 7 band graphic EQ pedal for fine adjusting the tone of the tube head.

    The whole idea with adding the tube head and another 15" to go with it was, beside increasing the overall potential volume of my rig, for it to function as a way to make me capable of blending in an over driven tone to spice up my fairly clean tone coming from the the solid state combo.

    As it is I am actually quite satisfied with the result, just letting the Orange Juice pedal do the job of overdriving the tube head, I guess I was just curious to look into what other options I had.

    As goes for the part about increasing the tube heads wattage by adding different power tubes, I guess that was more out of curiosity than any real need.

    Just to finish off, the Dynacord Bassking is equipped with 2 speaker outputs, and it is hooked up such that one takes 8 Ohm and the other 4 Ohm, as said at the moment I only use the 8 Ohm speaker output with one single small 1 15" closed cab.

    Output wise, at the moment, I have a lot more power to spare from both amps, at least at rehearsal levels in the small rehearsal space our power trio practice at.

    As far as I remember my Trace combo is not even 10 o'clock on the master and the Dynacord tube head is not even 12 o'clock.

    Thanks a lot for the input, makes things a bit clearer for me.

    Seems like I'd have to do with how I handle it at the moment, and at least for now just forget to get my tube head to overdrive on it's own.

    Honestly I don't mind much, I at least think it sounds pretty amazing, as I said earlier on in this post really just curious as to what other options I had.
    Last edited: Apr 2, 2017
  7. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    The best thing to do with it is buy it a power soak and get a clean gain pre to drive the whole amp into overdrive.
    The pre amp tubes ECC83/12ax7 are already 100 Mu, that's the highest gain 9 pin dual triode there is.
    There is no real gain advantage with any of the possible substitute power tubes.
    So just power soak what the manufacturer brilliantly designed and drive the input like you stole it.:)X
    NoiseNinja likes this.
  8. It sounds like you're looking for more preamp gain, but as has been pointed out, you're not going to get that by swapping valves. Looking at the schematic of the amp, the master volume does not work in the same way as most amps - it's part of the same passive mixing circuit as the channel volumes, with no gain stages in between the channel and master volumes. So unlike most amps, running the channel volume maxed / master volume low will get you the same results as running the master volume maxed / channel volume low.
    Unless you get into modding the head (which can be a challenge to do cleanly on a PCB built amp), then pushing the preamp with pedals is probably your best option.
    NoiseNinja, cdlynch and Zooberwerx like this.
  9. I'm also suspicious of running a 8 ohm load out of one output AND a 4 ohm load out of another output AT THE SAME TIME ,!!!!!! I'd check with someone familiar with this amp before doing that again. That's a 2.67 ohm load and your amp probably should only be driven down to 4 ohms. I could be wrong and frequently am but please check that out before doing it again. As you might release the magic smoke!
    Your two rigs running clean and dirty is cool but way more hassle than I'd be willing to set up and tear down.
  10. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    It means that you're not going to get appreciably louder output by changing tubes.
    You could cascade two of the input channels, the old Randall Smith/Mesa Boogie trick, but that takes a pretty considerable skill level, especially when dealing with the potentially lethal voltages of a tube amp.
    The easiest way to get what you want is probably with an overdrive pedal.
  11. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    This was my line of thinking, as well. This route would provide a more predictable outcome.

  12. Smooth_bass88

    Smooth_bass88 Groove it

    this is very intriguing. I need to try this with my recently re-tubed SVT.
  13. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    People try swapping (rolling) preamp tubes for different sounds and gains. In the case of this Dynacord, all three preamp/PI tubes are ECC83, or 12AX7, which are the highest gain variant of the 12A(TUVXYZ)7 family. So you can go cleaner, but not dirtier. Being a budget amp, the preamps probably don't have enough stages to get much overdrive.

    OTOH, a new set of tubes may surprise you. Forget about more power, though. For that you get a bigger tube amp.
    Last edited: Apr 1, 2017
    Fuzzonaut likes this.
  14. Kahrmine


    May 25, 2013
    You can possibly increase the wattage of your amp a bit by changing the power tubes to a different variety of the same tube. In other words, the EL34 type tube has a range with EL34 being a bit lower than the KT77 variety.

    Moreover, there are variations in tone between the EL34, the 6CA7, and the KT77 variety (all of which would work in your amp). You can get more headroom out of the KT77 than your typical EL34. Information on different options for EL34 type tubes and their tonal characteristics:

    www.thetubestore.com - EL34 / 6CA7 / KT77 Tube Reviews

    EL34, 6CA7, KT77 Differences? - Tubes for Amps

    The preamp section has a major impact on how much gain you can achieve, as well. There are varieties of 12AX7 type tubes that will yield more preamp overdrive or less. For example, a 12AT7 will have less gain than at 12ax7. A 12AU7 will even less gain than the 12at7. All preamp tubes have a unique EQ curve and may have a dramatic impact upon the overall general tone of the amp.

    There are so many variabls, the best thing to do is simply spend some money on different varieties and tubes and spend a weekend swapping and testing. It's a lot like a box of chocolates, and the circuit, the speakers, and your bass will all have an affect on how different tubes will sound.

    My opinion is NOS (New Old Stock) tubes sound the best and have the best construction for reliability and life. There are many varieties still available that are not much more expensive than the new construction tubes.

    I rarely buy new tubes unless there are no economical NOS varieties available.
    Last edited: Apr 1, 2017
  15. Kahrmine


    May 25, 2013
    Also, as a general rule, a lower gain circuit like a bass amplifier can typically handle higher gain tubes without getting annoyingly hissy. Guitar amps can sometimes suffer from such noise floors because the preamps are generally higher gain.

    The level of gain can affect the level of volume, basically. The higher the gain, however, the higher the noise floor of your amp when your not playing through it.

    In other words, I would try the 12AX7 or 12AT7 tubes as a 12au7 may be too low gain and lower your volume and keep you from pushing the preamp into overdrive if that's something you like to do sometimes.

    These are general rules and the many variables make it hard to say for sure how your rig will react to the tube swaps.
    Killed_by_Death likes this.
  16. Changing the preamp tubes can make it breakup faster, but you'll need to find a comparison chart someplace.
    I know Tube Depot has a nice comparison chart for 12AX7/ECC83 tubes.

    Welcome to TubeDepot.com!
    cdlynch and ThinCrappyTone like this.
  17. DavC

    DavC Supporting Member

    May 17, 2005
    Tallmadge , Ohio
    i think a lower gain preamp tube will break up sooner/smoother ... i use an old JG5751 in my pre ...

  18. As mentioned previously, stick to the tubes the amp was made for unless you know an experienced tube tech, and if you're willing to pay a ton for parts and a major overhaul of the circuit. You've already found that you get a good level from it, and @Killed_by_Death has the hookup for you with TubeDepot's comparison chart. Whether you buy from them or not, they do a great job of describing the variations for the same type of tube.

    If there's flexibility in the design for it, it might be worth finding out if the gain/volume setup can be changed to a more traditional design noted by @Martin Beer to give you the overdrive you want at a lower volume without a pedal. I'm not a tube tech, but that won't require tube or transformer changes. I just have no idea how invasive that mod might be, or if it would hurt the character of the amp.
    Killed_by_Death likes this.
  19. Ffreddy


    Feb 14, 2011
    I can't really make sense out of what you are asking. Do you want more overdrive or less?
    What are you trying to do by modding the amp?
    I just re-read the post and I am still confused.
  20. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Biasing the output tubes can affect distortion. Sometimes people use unmatched sets to provide more grit. Tubes can be bought that are selected for early onset of distortion. This means that they will distort sooner, the amp will be driven into distortion at lower volume levels. Ask about this when buying tubes, if they don't know what you are asking for go somewhere else.

    But I would set up the power stage for optimal performance with matched tubes that are optimally biased. For more grit, I would use a pedal at the input. Both, if driven hard enough, will saturate the input tube stage and provide an overdriven tone.

    There are two types of pedals to conside: A clean boost will simply saturate the first stage. These pedals tend to boost the high end as well. The second option is a distortion pedal. It will add grit of it's own and will also saturate the input if turned up enough.

    Another way to do this is to redesign the first stage of the amp to shift the operating point of the tube more into compression and distortion. Also, the two other channels can be modified to work better with an instrument input. These are fully reversible mods. Perhaps your tech might be able to help here.

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