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EL-84 tubes?

Discussion in 'Amps and Cabs [BG]' started by Lonesomedave, Dec 28, 2012.

  1. ok, as i've said before, there are no stupid questions...only stupid people who ask questions....so, here goes.

    i recently acquired an epiphone amp which uses 2 EL-84 tubes for it's output.

    my question: could i have my shop substitute EL-34's or 6L6's if they were biased properly? or are the EL-84's too small or in other ways would not fit the other tubes?

  2. tmdazed


    Sep 29, 2012
    im not entirely sure on your particular amp but some will require circuit modification done , physically they should be compatible, routing is totally different. Mu bugera has a switch that , I presume routs the 6l6 to a different path than that of the EL34
  3. no, no...my current tubes are EL-84's not EL-34's.

  4. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Time to edit your original post Dave. ;) EL-84 is much smaller and uses a different tube socket.

  5. :crying:

    oops...done...and you answered my question...smaller tube socket. got it.

  6. dincz


    Sep 25, 2010
    Czech Republic
    EL34 or EL84?
  7. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    There are plug-in converters going in the other direction, but I've never seen one going the way you are asking about.
  8. EL-84...as was pointed out, i mis-typed in my original post

  9. AstroSonic

    AstroSonic Supporting Member

    Dec 10, 2009
    rural New Mexico
    The 6L6, KT88, and EL34 would require octal sockets, a different output transformer and a higher plate voltage (and so a new power transformer as well). You would also need power supply caps and output stage coupling caps rated somewhat higher than the new plate voltage. Overall, this is a new amp. OTOH, you could more easily modify for use with 6V6's. There would be a modest decrease in power, but some prefer their sound over that of the EL84 (more common among guitar players).

    Stick with the EL84's. They are a good low power tube, and can provide plenty of power and great tone for a practice amp or for use on low spl gigs (coffee house, etc.). For an increase in spl (easily equivalent to going to 6L6's) replace the bass driver(s) with drivers having a higher sensitivity. A reasonably careful choice will also result in improved tone.

    What model is this? What can you tell us about the drivers and the enclosure (approximate cab volume, sealed, ported etc.).
    scf4003 likes this.
  10. it is a galaxie 25 guitar amp that i am thinking of swapping the speaker (12 inch celestion) for a ten inch bass speaker...it is a combo amp with a completely open speaker enclosure.

    i think your advice is good. don't modify the power tube section, just keep using the EL-84's that it was designed for.

    use as a practice amp, or mic to the board if we ever want to gig with it.

  11. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Completely open guitar cab = speaker death with bass. You can get a more robust speaker, I suppose, but I'd keep it a 12".
  12. You can get adapters for noval to octal bases, so you could fit the el34s in instead.

    I'm assuming your amp will be in cathode bias, so there shouldn't be any bias issues swapping the valves around aslong as the cathode resistor is large enough :)

    The plate load may be a little off but at that kinda power for musical instruments it doesn't make a huge difference. Btw don't expect a difference in volume. Valves can only shift as much current as they're supplied with, they aren't magic
  13. AstroSonic

    AstroSonic Supporting Member

    Dec 10, 2009
    rural New Mexico
    "It is a galaxie 25 guitar amp that i am thinking of swapping the speaker (12 inch celestion) for a ten inch bass speaker...it is a combo amp with a completely open speaker enclosure."

    This can still be a really nice practice amp for bass, but like JimmyM said, that open back cabinet will not work for bass. Most likely, the speaker and amp share the same space. The amp needs the open back for cooling (ventilation) so you can't just seal it up. You could make a plywood shelf just below the amp, close off the lower (speaker) portion and add a bass speaker.

    Perhaps the best alternative is to disconnect the 12 inch speaker and add a speaker jack. Then get a used bass cab with the same impedance as the 12 inch. This is the simplest solution, will provide the best bass performance and it preserves the value of the vintage tube guitar amp. Not as portable as a single cab, but with potentially far better performance. Old but working 115 cabs are rather frequently listed on CL for $50-$100.
  14. BawanaRik


    Mar 6, 2012
    New Jersey
    This is a bit esoteric but I think your swaps are limited to the 7189(?) tube.

    If you're going to play with amps I would recommend a older Tranyor. But since their original out put was some of the best amps ever made you really do not need to mess too much.

    Here's a link to the Duncan amp pages. Every tube roller needs this on their linklist


  15. actually, believe it or not, that work is already done for me. the internal speaker connects via a jack/plug, so all i have to do is pull out the plug on the guitar speaker and plug in my bass speakers...there are two jacks for speakers on the amp.

    this way, if i keep it, it will be a nice practice bass amp for my son, as well as a guitar amp for him also.

    i have already done this, and the sound is actually good, and loud enough for a practice amp...or to mic to the board in a gig situation. this eliminates the problem raised by JimmyM of an open speaker config. the two ten inch bass speakers are enclosed and made for bass

    i have used 2 old 10 inch bass speakers that we already had.

    the amp has some other issues, and i am debating whether to keep it. we got it for 189.00 at GC, used. i will need to spend @ 100.00 at my local amp doctor getting it fixed, new power tubes, pre-amp tubes (three 12AX7's) etc. the reverb does not work at all, and i am unsure if this is due to tube failure (12AT7) or what.

    we are returning it to guitar center today, and i am going to offer them 100.00 instead of 180.00. if they take it, i am going to get a new tube set and go to my amp doctor.

    i don't really expect this, so in all probability we will be returning it.

    thanks, to all who helped...:hyper:

  16. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Add to this the huge increase in heater current required by the octal tubes. Not a good idea to mess with what the amp was designed for.
  17. Alper Yilmaz

    Alper Yilmaz Gold Supporting Member

    Dec 5, 2005
    Brooklyn, NY
    Unfortunately, you cannot. They are different tubes.

    EL-84s are also sold under the SV-83 name and used mostly in SET amps in home applications. To the best of my knowledge, you can get around 2 watts per tube though, so I am not sure how well it will work in bass applications. In audiophile amps for home use, they need extremely efficient speakers, around 96-97 dB @1w1m for reasonable listening levels. Even then, the bass response can be quite problematic. Yet, with the proper speaker matchup and room treatment, they are to die for!



  18. well...this saga has taken an interesting turn.

    took the amp back to GC, told them of my concerns and offered them 100.00

    the guy looked at it and said- no wonder the reverb doesn't work...you don't need a new tube, someone took out the reverb tank!

    sooooo....they sold me the amp for 110.00...sweet! my son has a holy grail reverb, so that is no problem.

    took it by my amp doctor, and he will be out until next wednesday.

    get a new tube set (minus the reverb tube...:D), and have him go over it.

    i anticipate we will be up and running for a total 150.00 bucks or so, counting the purchase price of 110.00. (hell, we are already up and running, just needs some tuning.)

  19. you could change the EL-84s out for EL-34s or 6L6s, but the thing is, you'd have to re-bias the power tubes, use a new output transformer, and get some octal sockets etc... It'd take a lot of reading and doing, and by the end of it, you'd prettymuch have a completely different amp. You could probably get away with doing just one 6L6 or EL-34 in the power amp without having to switch out the output tranny, but it would still be a lot of specialized work.
  20. I'm going OT here, but do you know anything about the 50C5 power tube? I've got this PEPCO made single-end amp with one, I've been wondering if I could make a head-version of it that's got a push-pull power section using current production EL-84s instead of the 50C5 and still have it sound reasonably similar.