Different valves

Richardj

OK, I have seen that there are a few amps that can run on either EL34 or 6L6 valves, so I presume that electrically they are fairly similar.  What are the tonal, gain, response etc differences?

ThePrettyDamned

@icbm @martinw

Valvesign!

ICBM

EL34s have a bit more gain, midrange and crunch. 6L6s are a bit deeper, brighter and clearer.

Think 'Marshall' and 'Fender', but don't think the valves are the only or even the major reason for the difference! They simply bring out the inherent characteristics of the amp circuits a tiny bit. You can't turn a Fender into a Marshall by putting EL34s in it, or vice versa.

I recently specifically compared them using two Mesa Trem-o-verbs, which can take either. With both amps set to a 'middle of the road' sound - basically all knobs around 12 o'clock - there was actually almost no difference between them. The differences became more obvious when I tried to make one amp 'Fendery' and the other 'Marshally' - the one with 6L6s was much easier to make sound Fendery (and sounded better at it) whereas the one with EL34s was much easier to make sound Marshally (and unsurprisingly also sounded better at it). But each amp could still get quite close to the sound of the other even when using the 'wrong' valves.

So it's definitely more of a fine-tuning thing than a major tonal shift.

ecc83

When you look at the data for the two valves, especially the transformer loading differences, 5k6 for the 6L6 and 3k5 for the EL34 it is surprising that peeps find them as similar as they do when swapped in the same chassis!

Then, even a whiff of NFB will make them even more the same! I shall stick my neck out here and say the differences are mainly back in the PI that has to work harder for the Old Tetrode!

 

Dave.

 

Ossyrocks

They are not interchangeable in most amps, unless the amp is designed to do so, so don't try dropping a pair of EL34's in a vintage Fender or you may end up with smoke.

I think, although it's a long time since I looked at this, that you can sub a 6L6 into an amp designed for EL34's, so long as you re-bias, but not vice versa without modification

Rob.

ICBM

ossyrocks said:

They are not interchangeable in most amps, unless the amp is designed to do so, so don't try dropping a pair of EL34's in a vintage Fender or you may end up with smoke.

That's correct - and it's not just the pin connections on the valve base that's an issue, the EL34 draws much more filament current than the 6L6 and you can overload the power transformer.

ossyrocks said:

I think, although it's a long time since I looked at this, that you can sub a 6L6 into an amp designed for EL34's, so long as you re-bias

With most amps 're-bias' will mean changing a resistor or two in the bias supply since the voltage needed for 6L6s is much higher, usually outside the range of the trimmer.

martinw

In my experience (I've tried various amps with both EL34 and 6L6, as well as KT77 etc) the differences between output valves become more apparent when the output stage is overdriven. The cleaner the output stage runs, the less audible will be any differences, and I agree it's quite subtle. All of this is my opinion only and is subjective!

In a small, single-ended, cathode biased amp, the differences from one to the other are more marked. Also I build a fair few amps with Power Scaling, which allows you to take liberties with the output stage you often wouldn't be able to.

I hear EL34s as being more mid-focused with a tighter bass and a 'chimey' top end. They overdrive in a more pleasing way (to my ear). 6L6s are more balanced and as ICBM said, respond better to 'Fender-y' preamp signals with lots of bass and treble.

I prefer to put EL34s in classically Marshall sounding rock amps where the output stage will be pushed, and 6L6s in amps which are deliberately Fender-sounding, or high gain amps that need an uncluttered output stage. However, there are no rules, so it's whatever works for the user, and to some extent it's a choice governed by expectation.

For instance I love EL34s in single ended amps with about 10W for a lovely chimey sound that you wouldn't expect, and a great clean. Like a giant EL84.

jpfamps

ecc83 said:

When you look at the data for the two valves, especially the transformer loading differences, 5k6 for the 6L6 and 3k5 for the EL34 it is surprising that peeps find them as similar as they do when swapped in the same chassis!

Then, even a whiff of NFB will make them even more the same! I shall stick my neck out here and say the differences are mainly back in the PI that has to work harder for the Old Tetrode!

 

Dave.

 

The information you give on transformer loading is wrong.

The loading will depend on the operating conditions of the valves; for example increasing the HT increases the ideal loading (and vice versa).

The 3k4 loading for EL34 was used by Marshall and so everyone assumes that this is the "correct" loading for EL34s.

The loading used by Marshall is sub-optimal in most of their amps and causes excessive plate dissipation (this has been modelled in PSPICE by Randall Aiken, although it looks like his website is no longer functioning). A 4k load is "better" in most MArshalls, although this does cause larger screen grid currents.

Marshall used 4k in the JCM900 onwards (although this could be due to the first run being optimized for 5881s and Marshall not bothering to change the transformer!).

We use 5k6 with a pair of EL34s to give a gnat's under 30W. This loading is optimal for power (and in our opinion tone) under the conditions we use the valves.

There are several reasons for using 3k4 with EL34s; eg you are using off-the-shelf parts, or are trying to recreate a classic design, or that loading is optimal for the conditions you are using, or ignorance.

ICBM

jpfamps said:

Marshall used 4k in the JCM900 onwards (although this could be due to the first run being optimized for 5881s and Marshall not bothering to change the transformer!).

No, the first ones had EL34s. They switched to 5881s after a year or two, then back again later.

jpfamps said:

There are several reasons for using 3k4 with EL34s; eg you are using off-the-shelf parts, or are trying to recreate a classic design, or that loading is optimal for the conditions you are using, or ignorance.

I think ignorance is the most important component in a lot of guitar amp design .

That's not meant as a put-down at all, it's genuine. Knowledge is necessary in hi-fi design, but the goals are entirely opposite in most cases…

Classic examples of ignorance to me would be Marshall failing to adjust the NFB resistor value when they copied the Bassman and used a different OT, and Randall Smith cascading preamp valves way beyond the point of any sensible gain requirement. No 'proper' audio electronics engineer would do those things. But proper audio electronics engineers *did* design the CBS-Fender solid state amps!

jpfamps

ICBM said:

jpfamps said:

Marshall used 4k in the JCM900 onwards (although this could be due to the first run being optimized for 5881s and Marshall not bothering to change the transformer!).

No, the first ones had EL34s. They switched to 5881s after a year or two, then back again later.

I didn't know that.

I have to admit I wasn't that interested in the JCM900 when it come out.....

ICBM

jpfamps said:

I have to admit I wasn't that interested in the JCM900 when it come out.....

I was really interested in it - I really wanted one of the little Dual Reverb 1x12" combos. What a great concept - everything I wanted in a Marshall (albeit with shared EQ) in a tiny, portable package, with clever ideas like valve pair fuses, level-controllable FX loop, etc etc.

But I was puzzled that it only had three preamp valves… how, with all that functionality? JCM800 Split-Channels have five. So I opened one up. And then I went rapidly off the idea of owning one - actually not so much because it was clearly a hybrid amp, but because the build quality was so shockingly poor compared to the 800s.

Then when the DSLs came out I rediscovered a sort-of grudging love for the 900s .

jpfamps

ICBM said:

jpfamps said:

I have to admit I wasn't that interested in the JCM900 when it come out.....

I was really interested in it - I really wanted one of the little Dual Reverb 1x12" combos. What a great concept - everything I wanted in a Marshall (albeit with shared EQ) in a tiny, portable package, with clever ideas like valve pair fuses, level-controllable FX loop, etc etc.

But I was puzzled that it only had three preamp valves… how, with all that functionality? JCM800 Split-Channels have five. So I opened one up. And then I went rapidly off the idea of owning one - actually not so much because it was clearly a hybrid amp, but because the build quality was so shockingly poor compared to the 800s.

Then when the DSLs came out I rediscovered a sort-of grudging love for the 900s .

The greatest achievement of the DSL/TSL is to make the JCM900 look good, both in terms of build quality and sound....

ThePrettyDamned

I like how JC900's sound, especially the sl-x... 

Am I broken?

timmysoft

ThePrettyDamned said:

I like how JC900's sound, especially the sl-x... 

Am I broken?

I'm a big 900 fan!

ecc83

"The information you give on transformer loading is wrong."

That is the information I found in the GEC data sheet for the 6L6 and the Mullard  sheet for the EL34 . The 6L6 is 5k6  for Va=450, Vg1-37 and Pout=55W

Mullard give 3k5 for Va=400, Vg1 -36 and 54W . 

If others have found other loading are more useful then fine, I merely used those as a pointer to how different the valves were electrically, the 34 having for instance more than twice the gm of the 6L6. My point being that despite these differences many find the valves sound remarkably similar. 

Dave.