EL34 Champ or class A Plexi

[tubelovin]

I just built a champ and it sounds awsome. I really like the lower volume, and wondered if I could pop in one of my EL34's with a rebias. I'm using a mercury magnetics trans set.

Do you think that it would support the bigger tube? Would I need to change any Parts?

I was also thinking of trying a single ended plexi type amp. Anyone ever make one of those? What could I expect?

[MWJB]

I'm not familiar with the MM transformer specs but if your PT has at least 2.5A available on the 6.3v heater winding, and your OT will handle at least 10W/70mA (don't asssume anything, check with MM) then the only thing you "need" to do is to solder a jumper from pin 1 to pin 8 (assuming that there is nothing already soldered to pin 1, which there shouldn't be). It would be safest to upgrade the OT in any case, a multitap version would allow you to fine tune impedances.

Beyond that, you can of course rebias, however that will now exclude the use of a 6V6. Why not keep the amp biased for the 6V6 at 95% plate dissipation with a 5Y3 rectifier, then swap out to a GZ34 or solid state rectifier with the EL34 (making sure you still have enough voltage headroom on the main filter cap)? The EL34 will draw more current anyway and the tighter rectifier will add a few more mA still?

If that sounds OK you might want to leave it there, then you can compare 6V6, 6L6, KT66 & EL34. If you don't foresee going back to 6V6 then reduce the size of the cathode resistor (try 330ohms & 270ohms) and bias to 95% of EL34 plate dissipation. You will definitley need a beefier OT, say 80-90mA rating, if going this route.

[MWJB]

A couple of points that I overlooked...

Power tube cathode resistor - 10W rating minimum would be good.

Power tube cathode bypass cap - should be 50v rating minimum (with the bigger tube you may be seeing 40v+ on the EL34 cathode), I usually use 100v & keep some space between resistor & cap.

I always use over wattage/voltage parts here as a matter of course, hence it didn't spring to mind 1st time round.

[tubelovin]

Thanks for the replies. I think what I might do is contact MM and get the info on the trans and then try it out when I get all the parts. I like the amp with the 6V6 so I might make another if I like the sound with the EL34.

Have you done this tube swap before? What kind of tones did you get compared to the stock setup?

[MWJB]

Not done 6V6 to EL34 swap, but have done 6V6/5881/6550/KT88/KT90. As you go up to larger tubes headroom improves as does dynamic response. Different tubes and different brands of the same tube will accentuate different frequencies. For me, half the fun of having an amp like this is the "suck it and see" factor, rather than premeditating a tube type/tone.

The 'soul' of the amp essentially stays recognisable.

[tubelovin]

I totally agree about experimenting. What was yor favorite tube for that circuit? How much did those larger tubes affect the volume?

I would like to try a KT66 but don't have any on hand, just have 6V6, 6L6, and EL34 and figured I'd try the EL34 since it would give me a bigger difference compared to the 6L6.

[MWJB]

I play harp, and volume (dB) didn't change drastically. I ended up with an EH KT88 (which I don't actually like in any other amp) because it gave me the headroom & dynamics I wanted.

However, even with guitar, if you want to exploit the extra power potentially available then you're going to have to bump up the B+ (stiffer rectifier), improve filtering at the first and possibly second stages, bigger value uf cathode bypass cap (maybe even switch to fixed bias) and specifically bias each type of power tube to where it wants to be/sounds best, by experience/trial & error (95% plate dissipation would be your starting point).

A lot of work (relatively), a good learning experience, but will your amp end up as flexible and as much fun?

You could be pushing 10W+ with the bigger tubes? Apparent loudness will be dependent on other factors (speaker sensitivity, voicing etc.) as well as power output. However, my feeling is that if you want noticably more (giggable) volume and the headroom to keep with a drummer for instance, you're life will be easier with a push-pull amp.

A champ style SE amp is great for practice & recording, tube swaps are a great way to tailor the tone & response of the amp, the pursuit of power is less important to than the tone. You may find yourself trying to bang a square peg into a round hole if power/volume are your prime objectives.

[tubelovin]

I don't really want more volume but was wondering about it being more of a side effect of the tube change.

The reason I want to swap tubes on this and not my other amps is because of the low volume ( I live in an apartment) and it's simple and pure tone which seems to be perfect to really hear the tube and not the circuit.

I also thought of trying a single ended marshall type amp to maybe get a jimi page like tone at more modest levels. I've got a 100W Marshall now and it's too loud, especially for my house. Amps are always miked live anyways so it's not like you need that ear crushing vol.

I think small amps are where it's at. Almost every show I see people are using combo amps on stage, except for metal players. My friend says he plays a Fender combo with 6L6's and vol on 3 to4 his band is telling him he's way to loud.

[MWJB]

No reason at all not to build a SE amp with a plexi style preamp, several outlets offer something along those lines, check out Allen amps.

[Regis]

No reason at all not to build a SE amp with a plexi style preamp, several outlets offer something along those lines, check out Allen amps.

KOC has a whole section in TUT3 about building a "Dream Champ" including voicing it like a JCM800 and using different power tubes.

[teletroy]

I have a champ that I overbuilt so I could test different tube types in it.. and the el34 is my absolute favorite. I think I have a 12au7 in the preamp at the moment. I always get comments on the tone, and Im floored by it everytime I play it. It would probably be my main rig, but it still is in a cake pan.. I named it the betty rocker.

I like the 3 dollar chassis, I punch holes in the all day long just to try out new mods and I dont feel bad about it. This amp has so many switches and knobs, I dont remember what half of them do. Someday Im giong to take it apart and measure everything so I can just rebuild it with the exact values that it's set to right now because it's set at perfect.

[sjhust]

I built a G5, which is a French project. Single ended, TMB tonestack, takes an EL34, can be easily adapted to other tubes (using a 6l6 right now). Puts out about 10W, which is a problem when you play with a loud drummer and a crazy mesa-boogie alpha guitarist with crap tone, like I do. But it works fine with my quieter swing/pop band, and it's my #1 at home. You might want to take a look at the schematic; it's not complicated -> http://www.projetg5.com/Projets/G5/G5V2.gif

steven

[elpops]

I built a G5, which is a French project. Single ended, TMB tonestack, takes an EL34, can be easily adapted to other tubes (using a 6l6 right now). > http://www.projetg5.com/Projets/G5/G5V2.gif

steven

This looks like a great project--do you have any chassis photos and/or sound clips? I might just have to build one of these...

[tubelovin]

I haven't yet done the tube swap yet, I was building an 18watt. It's just a champ right now. Standard layout. I still want to do it but I just have to find the time. If you do one befor I do let me know how it works out for you.

[fabiomayo]

Hi, everyone.

I've been following these thread. I just finished my first build, a 5F1 Champ
with a defeatable tone control (almost useless too ). I used Mercury
trannies and even though I didn't plan to I was hoping to use different power
tubes too. Paul said it was ok to run 6L6 but that an EL34 might draw too much
current and cause the PT to run too hot.

I tried the 6L6 without any mods. I know it's not a fair comparison between
tube types without proper setting of operation points but I really liked this
setup. IMHO the top end remained pretty much the same but low end clarity
was improved. My first impressions were that the 6V6 were a bit sweeter
sounding even though the low end got very undefined at times. The 6L6 gave
the amp a more precise sound if that makes sense, with a tighter low end.
To me it appeared to increase headroom slightly and NO volume differences
to my ear.

For me, differences were subtle. I liked the better low end of the 6L6 and the
added 'spikeness' for some purposes. I'll probably stick with the 6V6. In any
case, not a great difference in feel, tone or volume to my ears.

Let me know what you think.