EL84 vs. 6V6 vs. 5881

I recently converted a Blues Junior to octal output sockets so it could run 6V6 or 5881s instead of EL84s. I’d done a couple of these years ago, but I had to ship one to Italy and the owner of the other one traded it away for a guitar, so I never got much time to dig in and experiment. I’ve had more time with this one and have some additional thoughts about output tubes.

As I mentioned on the “Very Special Blues Junior” page, output tube performance is largely about surface area. The more plate area you have for the electrons to hit, the more power you can push through the tubes. Of course, the cathode has to get bigger to emit more electrons, and the heater has to consume more power in order to boil off the additional electrons. That extra heater/filament power is often the reason that you can’t put larger tubes into an amp that is maxing out its power transformer. The transformer can overheat and the the voltages in the amp can sag under load as you increase the volume.

I was concerned about heater load when I did the conversion, and wondered if I would be limited to 6V6s or whether I could go to a bigger tube in the same family, namely the 5881, also known as the 6L6GB. The 5881/6L6GB has a maximum plate dissipation of 23 watts, compared to the 30 watts of a 6L6GC. So I did some measurements of filament power consumption. Here’s what I found:

The stock EL84 is supposed to draw 700 milliamps of filament power. I tested a bunch of them and they all drew between 830 and 845 mA. 6V6s are roughly equivalent to EL84s electrically, but they were designed for 1950s car radios, so the filament is designed for 450 milliamps to help conserve the battery. This table shows what I actually measured for a single tube:

Tube Heater draw, mA Plate dissipation, W
EL84 830 12
GE 6V6GT 580 14
Electro Harmonix 6V6GT 560 14
JJ 6V6S 650 14?
Tung-Sol 5881 980 23

As you can see, the EL84 is almost as power-hungry as the 5881, but is only about half as powerful in terms of wattage. The NOS GE 6V6 and the current-production EH 6V6 are essentially the same in power draw. This is a small sample, but it appears that 6V6s never quite met the 450mA spec.

The JJ 6V6-S is an interesting case–it draws more heater current, but not as much as the 5881, yet its plate structure is almost as large as the 5881. I’m sure it’s capable of higher output than the traditional 6V6GT. It’s often used in 40-60 watt 6L6 amps where players want less power and headroom, earlier breakup. Among 6V6 tubes, it’s the only one that can handle the high plate voltages of these amps.

In these pictures, you can see the plate sizes and get a feel for where the power handling comes from:


From left to right: JJ EL84, GE NOS 6V6GT, Electro Harmonix 6V6GT, JJ 6V6-S, Tung-Sol 5881. When we turn the tubes a bit, you can get a better idea of the difference in plate size:


The EL84 packs as much plate as it can into its noval (9-pin) envelope. The 6V6GTs are thin, but the 6V6-S and the 5881 have large, boxy plate structures that gives a lot of surface area.

Putting larger tubes with higher wattage ratings into your amplifier won’t automatically give you more power or a louder amp. The actual output power is determined by the power supply, the output tube, and the output transformer. But larger plates generally mean better bass performance. But running a “big” tube designed for higher voltages at a lower point on its operating curve limits its headroom and provides earlier/different distortion than you’d experience at higher voltages. In fact, you could put 6L6GCs in there because they have the same nominal 1000 mA heater draw as the 5881/6L6GB. But the additional plate area won’t help because the power supply really does run out of gas at some point. The 5881s can’t produce maximum power, so larger tubes won’t either.

In terms of my Blues Junior mods, it comes down to this:

  • The Blues Junior has enough power supply headroom to run larger output tubes
  • The greater current draw of the 5881 does not cause appreciable high voltage sag
  • If you go for octal socket conversion, there is no reason not to run 5881s as opposed to 6V6s
  • With other mods in place, maximum output is bumped to around 25 watts, limited by the power supply

The JJ 6V6-S bears further investigation. It consumes less heater power than an EL84 but has significantly larger plate area. In the future, I’ll do some power/tone comparisons with the 5881, but it appears that the JJ would be a great choice for 2 x 6V6 amps like the Princeton Reverb, Deluxe Reverb, and Super Champ XD.


  1. Patric says:

    can octal sockets be put in a fender pro junior? can a pro junior run 6v6 tubes?

  2. Ricky says:

    So can a BJ be converted to 6V6s and then use Yellow Jackets to run back on El84s when the mood strike you?

    • bill says:

      Well, yes, you could, but the Yellow Jackets wouldn’t sound much like the stock Blues Junior. They’re cathode biased and the output power and headroom would be lower than stock.

  3. Simon says:


    Iv recently done most of your Mods via my local friendly Amp Engineer over here in London, namely Tone stack, twin stack, power stiffening and the upgraded transformer from your self. I didnt do the cathode follower Mod.
    Im now intrigued by the idea of sticking some 5881’s in along with the cothode follower Mod.
    I have found some 5881’s from Watford Valves here in London “5881/HARMA-CRYO” the cryo treated ones.
    What would you recomend as a good match to upgrade the 12AX7’s?
    I’m idealy looking for more clean head room and a nice warm spongey clean sound which I can then drive with pedals?

    • bill says:

      The 5881 conversion is not a clean headroom amp by any stretch of the imagination. It’s a bit louder in the clean range, but it’s mostly a growly, down-and-dirty blues amp. The 5881s would need a lot more plate voltage for more clean headroom. I think cryo tubes are a waste of money.

  4. prodatlantis says:

    I Bill,

    First thank’s for your mods!!!!

    What do i need for replace EL84 by 6L6? What have i to do?

    It’s for use with a rhodes, i’m looking for more bass.

    • bill says:

      I think the Blues Junior is the wrong amp for a keyboard. Even with more power, an open-back amp is never going to produce as much bass as you probably want, unless it’s a big cabinet with more that 40 watts available.

      The BJr power transformer can’t deliver enough power to run 6L6s effectively. I would recommend a solid state amp with a closed back for your Rhodes. It doesn’t have to be expensive to sound decent.

      • Jeff H says:

        Bill, if I may – the “reference amp” for voicing and tuning of the Stage model Rhodeses at the factory was the Fender Twin Reverb and the speakers in the cabinet of Suitcase models were open on both sides. The Rhodes Stage output was at guitarlike levels and impedances and worked just fine with tube or solid state guitar amps; the Suitcase models and the Satellite speaker cabinet sets used solid state amps.

        Prodatlantis might consider an honest-to-goodness FTR or a Dual Showman with the 15s if he wants to stick with classic Fender amps, but your recommendation is still very valid. My brother used a 1970s closed-back Epiphone amp with a single 15″ for his Stage 73.

  5. ou812 says:

    Three of my favorite mods, which I’ve done a number times are: install 6V6 power tubes in a blackface (or silver face) fender head, convert to Cathode Bias (500 ohm 10 watt resistor, 10 microfarad bypass) , and then add tube driven reverb (use the bass channel tubes for drive and return). The Bassman comes close to being perfect with these mods…
    I really don’t think the BJr can handle 6L6 power tubes. The power transformer just doesn’t have the juice to do them justice and I’d bet that if you played it that way for a few hours the power trany would be too hot to touch. I like the 6V6 mod however. I think Cathode Bias sounds good as well (300 ohm 5 watt resistor, 22 microfarad bypass), it adds a little grain and sparkle. I have never found cathode biasing to rob all that much power from an amp. Everybody says it will, but I don’t hear it, and I’ve tried it on probably 20 different amps…

  6. Miklos says:

    The heather current of the EL84 is 0.76A

  7. katoosh says:

    I know your not a huge proponant of Mercury Magnetics OT. But I would imagine them to be up to the task, as long as your pockets are deep enough. Yes?

  8. Misisipi Mike says:

    Is there any purpose in moding a pro junior? If so, what are the most common?

  9. Chris says:

    I enjoy these smaller combo amps etc and actually thinking of building one in the future for fun. Would it be worthwhile using 6v6 instead of el84? is there really that much of a difference in volume, clean headroom? Thanks. Great job on your newest mods and fun with the blues junior.

    • bill says:

      Every output tube has its characteristic tone, and the 6V6 is glassier, airier than the EL84. The EL84 has a great grind tone, however, so it comes down to taste. The difference in volume is rather small.

      • Eric Bernhardt says:

        I really don’t like the grind tone (I try to avoid it). I like a Deluxe Reverb sound (cleaner) and it uses 6V6 for output tubes. So would you say 6V6 for my BJ is that way to go?

        • bill says:

          The 6V6s will grind, too, but will sound bigger and rounder. It’s a blues amp, after all, and it has two stages of gain before the tone stack. Try a 12AY7 in V1 to reduce the preamp gain. It’ll give you a bigger range of control over the clean tones and delay the onset of the distortion.

  10. Ken says:

    I have a pair of JJ 6V6’s I would like to put in my Super Champ Xd to replace the Stock Groove Tube Black Glass. What should I bias to? 40 as usual?

  11. john says:

    I just purchased a super champ XD.. . two nights ago I played bass to a guitarist with a super loud modded Blues Junior(OT modded) Will these tube mods work on a super champ too? Will it match up the that BJ in volume?

  12. mark says:

    hi bill…have you ever changed the power transformer and ran 6l6s?..i really would love to hear what it would sound like.

    • bill says:

      There is no PT that fits and provides all the right voltages. You would have to completely rework the bias circuit, too. Better to cut down a Blues Deluxe!

  13. mel says:

    hi bill..is the cathode follower mod just as easy to do with the 6v6s as with the el84s? your diagrams show how to do it on the EL84s but wahts does it look like with the 6v6s( i mean the pcb socket holder part)?

    thanks Mel

  14. MEL says:



  15. wm says:

    I saw an article about Neil Young’s tweed deluxe that he runs 6L6’s in, and has a fan on the amp… would putting a fan on it in this case help? what about a different back panel that gives it a little more ventilation? Also I saw a pic of a Kendrick amp that has a clear plexiglass back panel so you can see the circuit… would that work on the Blues Jr or doesn’t it need to have shielding foil on the inside?

    • bill says:

      I’ve installed fans on a couple of Blues Juniors. There’s a simple circuit that draws power from the filament line and converts it to DC. A clear back panel is just for show–you really should have the shielding.

      6L6s/5881s fully load the BLues Junior’s power supply; there’s barely enough power on tap to get full power out of the 5881s, not enough bias voltage for 6L6GCs.

  16. Jesse O says:

    Have you ever encountered mechanical tube rattle? Combo amps are the worst for it and so are El84’s. My blues jr. has this problem and I was thinking about putting 6v6s in because they are less prone to rattling.

  17. mike says:

    hey bill…can i put a choke on my bj?..would it be worth it if you can?

  18. mike says:

    hi bill..why is that? it would be easy enough to do , wouldnt it?..i thought you would have experimented with one by now.

  19. Vince says:

    Bill, I’m running JJ 6v6 biased at 24ma in my PRRI. Do you think this is okay, too hot? I’ve read that you think they can take abuse, but just want to confirm I’m not pushing things too much. As an aside, do you have a preferred bias for JJ’s in the PRRI? Thanks in advance if you have time to offer your thoughts….

    • bill says:

      I’m going to assume that your plate voltage is around 375 volts, which is typically what I see in PRRIs. That would make your idle 9 watts, which is fine for the JJs. I generally go for 50mV on the 1 ohm resistor with the JJs, which is 25mA per tube, essentially the same as your setting.

      • Vince says:

        Thanks again for the response. Makes me feel better that I’m probably going to melt my amp to the ground! By the way, I just read on Jim Campilongo’s site that he biases his PRs and PRRIs at around 30 per tube. Sounds crazy to me, but he does sound pretty good….

  20. Maxim says:

    Have you had any experience using an EL34 output tube pair (or wise advice thereof!), thanks over many times

  21. dan smith says:

    hi Bill,i just got a blues junior and wanted to get more clean headroom and volume from it to use with my archtop for wes,benson,green kind of stuff and i wondered what you would suggest i do to it and just which mods i should use?.regards.Dan.

    • bill says:

      The basic mods, TwinStack and presence control will give you far more tonal flexibility. The TO20 output transformer will give it a more professional, “boutique” tone.

  22. Daniel Yakel says:

    So, if I wanted to tame the excessive high end that the Blues Jr has but keep as much clean headroom as possible, would converting to any other tube type help at all? I like a crystal clean amp, then drive it with pedals.


    • bill says:

      I think the issue with the BJr is not excessive high end, but not enough low end to balance it out. That’s what the basic mods do. Tubes won’t help. A darker-sounding speaker might.

  23. bluesjunky says:

    Hey Bill, have done all of your mods including the octal mod on may BJr NOS. With that mod you sent me the JJ 6V6-S tubes. I have read your evaluation and am still not sure if the JJ’s or the Tung-Sol 5881 are that much different as far as tone. I like the JJ’s but I am always tinkering with everything I own so I am curious about what the Tung-Sol 5881’s will do to my tone. It has be a joy doing all of the mods and seeing the results. Are we maxed out on BJr mods yet or are you still tinkering? Regards, John

    • bill says:

      Remember, you use 5881s at your own risk. They’re a little rounder/deeper/fatter than JJ 6V6s, but they tax the power supply heavily.

      • GWM222 says:

        I am VERY NEW to this tube stuff… can you explain what the consequence would be as ‘basic’ as possible, because I was thinking of using the 5881’s also as I want the ’rounder/deeper/fatter/ tone. And what if you were to use the 5881’s in the Champion 600?

  24. Rambler says:

    With the basic mods, the octal conversion mod and the addition of the T020 output transformer could I run 6L6GC output tubes like the Blues Deluxe? Would there be a wiring difference? If I could run them with your octal mod and since the 6V6’s can deliver about 25 watts of clean power, what could I expect to get with the 6L6’s or would I have to upgrade to a Blues Deluxe type output transformer? I ask this mainly because I have a spare set of Groove Tube 6L6’s I’m not using.

  25. druce says:

    I have stock tubes in my blues Jr and want to change the tubes. I want to go with the same tubes but only in JJ’s, brand. can I just replace them without doing any thing to the amp?

    • bill says:

      Yes, you can just plug in new tubes and not do anything. The output tubes may be running hot, but the amp will still work OK. I like JJ EL84s; the ECC83/12AX7, not so much. The standard Sovtek/Fender/Groove Tubes 12AX7 is a better tube.

  26. G-Man says:

    Hi Bill,
    Are there any considerations as far as speaker impedence when going to the 6V6’s? ie: go to a 16 ohm speaker.

    I was looking at changing the EL34’s in my Rivera R55/12 to 6V6’s and there was talk of going to a 16 oum speaker as part of the mod. That’s why I ask.


    • bill says:

      EL84s and 6V6s have the same plate impedance, so the same output transformers and the same speakers work equally well for both. EL34s and 6L6s have about twice the impedance, so a 16 ohm speaker is a more perfect match. But most any tube amp can tolerate a 100 percent mismatch, so you’d just lose a little bit of efficiency.

  27. Gregamonster says:

    Do you suggest this 16 ohm speaker would work better on a Super Champ XD as well?
    BY the way, I have converted a Super Champ XD to 5881 tubes using stock power and output transformers. Love the tone! I found your site while looking for data to back up my theory that this could be done. So many folks assume this amp will overheat with 5881 tubes. I ran mine continuously for 24 hours and the power trany just got comfortably warm. Filament holds at 6.4 volts and plate drops only to 360volts at full volume levels. This is pretty normal for any amp design.
    My theory is these power transformers were built more universally with a full compliment of tubes in mind. Since the Super Champ XD has DSP front end instead of tubes, there is extra filament current available.
    Just to be sure it would all stay cool, I added a 3 inch fan behind the power trany. A 12 volt fan runs quietly on the 9 volt supply available in this amp. I also added a 22k resistor with a switch across R30 in the bias supply to allow switching 6V6 or 5881 tubes without pulling the chassis to re-bias. The bias trim can still be adjusted to set the range. I set mine at 33ma for 6V6 and 38ma for 5881.
    Love your forum here!

    • XDaddict says:

      Interested in your 12v/3″ fan idea to cool my XD. Where did you take 9vdc feeds for it from (in layman terms please). Where did you purchase the little quiet fan and is it bolted directly to chassis near transformer. Any problems caused by doing this i.e loss of volume or hum etc? Thanks.

      • bill says:

        In my experience, XDs don’t get hot enough to require a cooling fan.

        I got the fan out of an old computer and built the supply circuit off the 6.3V heater circuit, using a diode bridge and capacitor. The diode bridge gives you 1.4 times the AC voltage in DC and the capacitor smooths it out. I thought I had a diagram on my site, but can’t find it.

  28. alecaster75 says:

    Hi Bill I’ve done the following mod’s so far, Cream board Basic, TO20 Heyboer, Presence control, Recap Kit, and Cathode follower.
    I had some problems with oscillations. Well I rerouted the ribbon cables as you said, I had to change not only V3, but also V1, V2, V4 and V5 to finally solve the problem.

    I’ve been playing with the amp for while. But now I’ve changing to 6V6’s and I can’t get them to -4.2v, they are over -5v and -7v.

    • bill says:

      What’s the maximum voltage you can set on the top leads of R31 and R32? You should be able to get a full -26V out of the bias adjuster, which should be enough to cool down the 6V6s.

  29. eddie_bowers says:

    If I do the Octal conversion, do you have any idea if I can use these to go back to EL84
    I don’t think they work like the Yellow Jackets and are just a Pinout converter (but that’s just me guessing from the size)

    • bill says:

      It looks like they would work. You could check them with an ohmmeter and return them if there are any internal connections or resistances.

      • eddie_bowers says:

        Just wanted to report back that I got some and they check out to be simply pinout converters. I won’t get to try them out for real until I do my Octal conversion. This gives me a fallback position if I miss the way it used to sound.

  30. scott says:

    i am thinking about the 6v6 octal socket mod (since i have the T20 & PT24). Would I have to get to the back of the main board to do this mod? i’m trying to figure out the difficulty of this mod.

    • bill says:

      You do have to get to the back of the board to solder the wires and replace a few components. You also have to be able to drill some small (#38) holes, drill the circuit board with the little drill that came with your basic mods kit, and cut the circuit board cleanly. It’s the most difficult of the mods, but lots of folks have completed it successfully.

  31. bluesjunior says:

    Hi Bill, I did a stupid thing the other day and used too much heat while re-soldering the pins on the V5 output tube resulting in lifting a couple of the metal pads/rings. I have had a look through the site and read your article on simple PCB board repairs and was thinking that was what I would most likely do. Then I came across this thread here and thought that perhaps buying two new 9 pin valve sockets with collars and mounting them direct to the chassis might be a better solution but am not sure if that is possible as it would mean cutting off the part of the board which holds the power tubes at present. Correct me if I am wrong but it appears you are doing something similar here with the 6V6 mod although I would prefer to keep the EL84’s. My BJr’ is a green board version if that makes any difference. If this was possible I would be willing to pay you for an instructional schematic or diagram?.

    • bill says:

      You should make wire loops for the pins where the pad has lifted as shown on the “PCB mistakes” page. I don’t know of any 9-pin sockets that will fit in the holes on the chassis. Unless you’re a metalsmith, it’s a hassle to make adapter rings to mount the sockets.

  32. Joseph says:

    I have been looking around the site and I am just curious, if I want to have my Blues Jr. use 6v6 tubes what all do I have to do? at the very least? optimally? thanks in advance.

    • bill says:

      The basic mods, octal conversion kit and a TO20 or TO22 output transformer is the very least you need to run 6V6s. You can go as far as you want with the other mods. The TP24 and bias board will give you full power from the 6V6s, and more punch.

  33. durhadj says:

    I’m also just curious… Lets say you’ve already done the basic, presence, sparkle, clean boost, & twin-stack mods & installed a TO20. 

    If you only added the octal conversion, would there be a noticeable tone difference when running 6v6’s (as opposed to EL84s and no octal conversion)? 

    • bill says:

      Yes, there’s a tone difference between EL84s and 6V6s. EL84s are noted for glassy, harder tone, while 6V6s sound more open and airy. The 6V6 plates are a little larger, too, so you get a bit more bass with the 6V6s.

  34. marchallam says:

    Hi there.
    I love the sound of my bjr3 (especially after your mods) but i need more volume. Without getting too specific, do you think it would be possible to add another pair of el84’s in parallel? Obviously it would need a bigger cab/chassis. If i installed another small power transformer to supply the heaters, would the stock power transformers be able to cope and also would either of the output transformers you sell be up to the task?

    • bill says:

      Quad EL84s is a bad idea–too much heat, no room, great expense in swapping to a new chassis. The 6L6 conversion works in the existing cab and gives you twice the wattage. That’s not twice the volume, however, and it does change the tone somewhat.

      The least expensive solution is to mic the amp.

  35. buda says:

    Hello Bill I wanted to know if there is any way to mod the green board to receive 6v6s

  36. johnniewillits says:

    Ok so I no longer have my Blues Jr, but now have a Peavey Delta Blues 210. It’s a 12ax7/el84 30w amp and I am giving serious consideration to converting it to 6v6s. Do you have any suggestions or comments on this?

    • bill says:

      I’d say it’s somewhere between extremely difficult and impossible. The sockets are PCB-mounted, you have series filaments, cathode bias, and not a lot of room to work. Peaveys are difficult to work on anyway; I personally would not consider trying this.

      • johnniewillits says:

        Thank you, I’m glad I asked before I started investing any time or money into that idea. I’m now just planning on going with a Blues Deluxe or Deluxe Reverb now. I just can’t dial in the tone I’m happy with on this Peavey. Thank you for your advice.

  37. Slestak71 says:

    Hi Bill. I did many mods on my BJ years back and have loved it. Been really thinking about this octal mod. Just a question for you. I found on Ebay a set of socket converters to go from 6V6 to el-84. Not the Yellow jackets mind you, just a plain socket to socket converter for plugging 6V6 tubes into an EL-84 socket. This would allow switching back and forth between the two types of tubes. Also if it works it would allow me to not have to do any cutting. Do you feel that this would work, or is there more to the mod than just changing the sockets? Thanks for all that you do for us hopeless tinkerers.

    • bill says:

      The 6V6s need larger coupling capacitors from the phase inverter, so they would sound a little thin with the stock caps. They also need different bias voltage.

  38. owen247 says:

    Hi Bill,
    I have not seen much talk of Mesa Boogie EL84’s on the site (MESA BOOGIE EL84/6BQ5 POWER VALVE DUET)
    – are they a bad choice for a Blues Jr. – or are they all the same? Anyway, I’ve ended up with a pair, and seeing as the current tubes in the amp are flashing blue fire inside – I think I need a change…

    Can I bias them the same as any other EL84 (2.6V – stock Transformer)

    I’ve seen some people say that mesa tend to run their amps hot and these are used in amps with fixed biasing.
    – I have some of the mods in my amp and so biasing is not a problem, but any advice appreciated.

    • bill says:

      Mesa doesn’t make its own tubes. They buy in bulk from Sovtek and other manufacturers. Every Mesa EL84 I’ve seen has been made by Sovtek, same vendor as Groove Tubes. I think they’re good-sounding, hardworking tubes.

  39. Slestak71 says:

    Went ahead and just did the octal conversion and been running the Tung Sol 5881’s. Was able to get bias down to 5.8-6.2. Like KISS said in “Firehouse” WOOOOOO WOOOOOOO YEAH!!!!! I see no reason to ever want to go back to EL-84’s Thanks a TON Bill.

  40. Texifornia says:

    Interesting reading. I have had my Blues Jr. for about 10 years, and done nothing to it but plug in. I am thinking about doing some of the mods listed on the site, but reading this thread has me wondering about tubes. Is there any guidance on brand? A quick web search for reveals that EL84s range from $9.98 (Sovtek) to $199.95 (Telefunken). 5881s range from $19.98 to $89.95. How do you choose?

    • bill says:

      Your amp will only take EL84s unless it’s modded. Groove Tubes/Sovteks or JJ EL84s will give you good, reliable performance. I try to discourage people from doing the octal conversion (6V6, 5881, 6L6) on green board amps.

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