el 84 characteristics

[rhp52]

Typically, what are the sonic characteristics of el84 tubes?

[DIXØN]

Bright and chunky, think Vox AC15/30, Fender Blues Junior, Fender Champ, and Epiphone Valve Junior. Nice when pushed into overdrive especially with a Celestion Vintage 30 or Blue. The design of the output stage does also count, for example the Champ and Epi Junior are single ended class A which = harmonically rich, the others are push pull and class AB, with the exeption of the Vox's which are pure class A also.

[rhp52]

thanks Dixon and welcome to TGP..Anybody else care to chime in?

Is lack of bottom end typical for A/B?

[VacuumVoodoo]

thanks Dixon and welcome to TGP..Anybody else care to chime in?

Is lack of bottom end typical for A/B?

No, it's a matter of over all circuit design and often a too small and badly designed output transformer.

None of the Vox push-pull amps is class A, they are class AB. It's a myth that a power amp is class A by virtue of self biased (aka cathode biased) power tubes.

[RedMan]

I agree, overall design has a lot more to do with it than tube type.

[Timbre Wolf]

Is lack of bottom end typical for A/B?
I actually disagree, somewhat, with VacuumVoodoo's post. There is a change in ability to produce tight low-end, when considering power-section operating class. Fixed (or adjustable) bias class AB can give a much more percussive low-frequency attack than cathode-bias AB or single-ended class A, which are softer in this regard. Most "classic" examples of EL84 tube amps do not have a fixed-bias power design.

I do agree that transformer qualities, etc. come into play as well, but are not as influential as the operating class when considering tight, percussive bass. None of this is tied to the EL84 itself, though, which was the original point of the question. I would say that the power tube type is less important than the power section design and component types.

- Thom

[rhp52]

Thanks all! So if i am reading this correcly, the low end is a result of circuit design and output transformer size? Would changing to a bigger output transformer itself be useful without and other changes?

[VacuumVoodoo]

Thanks all! So if i am reading this correcly, the low end is a result of circuit design and output transformer size? Would changing to a bigger output transformer itself be useful without and other changes?

Roughly, yes. Don't forget the loudspeaker in the equation.
One must take all system parameters into account. Lets say you have a fixed bias 4xEL84 amp with a properly matched output transformer and a preamp tweaked ad voiced so your low end is punchy, tight and fine. Now change to self bias. It's a completely different amplifier. Firstly even if the plate supply voltage stays the same the voltage that tubes work with changes by the amount of voltage developed on the cathode resistor(s) it can be 14 to 20V in this case. Cathode bias also changes tubes' internal plate resistance, this in turn will require a different load impedance i.e. a different transformer. Then we have a question whether cathode resistors are bypassed with capacitors or not and how big they are.

What does it tell us? - Everything is connected. When you're not happy with the sound of your amp it's difficult to blame just one section of it. You have to look at the whole system.

[Axekisser]

The Champ is a 6V6 amp, not an EL-84.