EL84 vs 6V6

[crgfrench]

In his 1994 classic, “A Desktop Reference of Hip Vintage Guitar Amps”, Gerald Weber devotes 7 pages to his thoughts on the determinants of tone, in his chapter “Amps of our times - vintage vs. modern”. I suspect that, if we were able to quantify the contribution to tone of the various parts of an amplifier, we would find something like this (for a given guitar and a given circuit): Tubes = 50%, Cabinet & Speaker = 35%, Passives (capacitors, resistors, wiring, board type, solder etc.) = 8%, Transformers =6%, with less than 1% determined by “magic”, “mojo”, “voodoo”, or “vibe".

Or at least, that's what I used to think.

I bought an Egnater Rebel 20, it's a very interesting amp with a pair of EL84s in push pull and a pair of 6V6s also in push pull. You can select either pair and you can blend them with a dial. I was surprised how little difference there is in the tone between the two. It's barely distinguishable at all (at least to my old ears). I had always thought the tube type makes a huge tonal difference.

Egnater's website has a discussion about this topic; Bruce explains: "when panning from the 6V6 tubes to the EL84 tubes, the tone difference is not what some expected. It is believed that by simply changing power tubes you can make a Fender (6L6 power tubes) sound like a Marshall (EL34 power tubes) or a Vox (EL84 power tubes). What you are hearing in the Rebel when you go from 6V6 to EL84 is the real difference in the sound of those two types of tubes. It may not be quite as dramatic as many believe but that is the reality of it. The tonal difference between various types of tubes is more subtle than many believe. A few people have even been disappointed when using the TUBE MIX features because their expectations of what should happen were really not based in fact. The intangible characteristic is the change in “feel” between different types of tubes. These subtle differences do become more apparent at higher volume when the power tubes are “pushed” a little more into overloading. What you are hearing in the Rebel is “the truth” about power tubes."

Now to be fair I haven't spent much time with the Rebel 20 cranked up to 11. Perhaps the difference is most apparent then. But at this point I'm revising my prior model to be Circuit = 90% and all the rest as follows: Tubes = 1%, Cabinet & Speaker = 3%, Passives (capacitors, resistors, wiring, board type, solder etc.) = 3%, Transformers =3%.

Or, maybe it's really ALL “magic”, “mojo”, “voodoo”, or “vibe".

20200120_144343.jpg

[JMPGuitars]

Your breakdown is a little off IMO. Yes, the circuit probably matters the most. BUT, the important point is that the circuit should be designed for, or at least properly compliment the tube(s) in question.

I've played that amp you're talking about. I thought it was a fantastically bland and lifeless thing. If you have a lifeless circuit, the tubes won't sound great, no matter what they are. You could probably mod it into something more interesting.

Years ago I modded a Traynor YCV80 to switch between 6L6 and EL34 tubes. I don't think that circuit was anything special compared to the circuits on this site, but it certainly was tastier than the Egnator. As usual, I preferred EL34s in the amp.

The other issue with that type breakdown is that any single component being poorly matched will diminish the rest of the amp. Bad tubes, weak iron, bad (or poorly matched) speaker, mediocre cab, etc... will make an otherwise nice amp sound like trash.

That's probably why certain components have so much mojo associated with them. Compare one good brand of output transformer to another, and it's not so noticeable (if at all). Good is good. Compare it to whatever lame mass-produced, underspec'd junk the manufacturer put in there, and any good OT sounds amazing.

[colossal]

Compare one good brand of output transformer to another, and it's not so noticeable (if at all). Good is good. Compare it to whatever lame mass-produced, underspec'd junk the manufacturer put in there, and any good OT sounds amazing.

This ^^

Taking this a step further with the 18W....the output transformer and specifically its construction method and materials will have a significant impact on this amp's sound. Avoid cheap imports! The devil is in the details

[Daviedawg]

"The devil is in the details". Most definitely true for any amp.

Also Merlin (Valvewizard) says that what you hear in any amp is the power supply. The more amps I build the more I recognise what he is saying. It reflects what Josh and colossal are saying above. Get that wrong and no amount of mojo will bring it back.

Dd

[geoff 1965]

good points! plus any amp that blends tubes has to settle on a medium for both types i.e. plate voltage,phase & biasing,so to bring out the best in the el84's you would have to compensate the 6V6 values.we know the best plate voltage for the 18W is around 345V for the el84's whereas the amps with a good reputation for 6V6's like the champ and tweed deluxe have over 400V on the plates.
i would rather have a designated output tube and tweak that type to bring out the best.

[colossal]

good points! plus any amp that blends tubes has to settle on a medium for both types i.e. plate voltage,phase & biasing,so to bring out the best in the el84's you would have to compensate the 6V6 values.we know the best plate voltage for the 18W is around 345V for the el84's whereas the amps with a good reputation for 6V6's like the champ and tweed deluxe have over 400V on the plates.
i would rather have a designated output tube and tweak that type to bring out the best.

As an aside on this about Champs and Tweed Deluxes...modern mains voltages make these amps run way too hot. Their (Triad) PT primaries were wound for 110VAC. At my mains, I routinely see 123.5VAC. Other places I have lived, even 125VAC! Terrible for these old amps causing the tubes to run way over max dissipation. The resulting sound for running 6V6 plate voltages that hot, IMHO, can be hard and blatty with a fatiguing and sometimes strident top-end. A Tweed Deluxe running 350-360VDC on the plates sounds (with lower screens) much smoother to me. YMMV of course as sound/feel is a personal thing.

I definitely agree about the "18W sound" being right in the 340-350VDC pocket on the plates and 20VDC lower on the screens. With Voxy voltages and roughly the same circuit (low 300s on the plates and lower on the screens) the sound is very warm and lush, but less articulate.

[JMPGuitars]

good points! plus any amp that blends tubes has to settle on a medium for both types i.e. plate voltage,phase & biasing,so to bring out the best in the el84's you would have to compensate the 6V6 values.we know the best plate voltage for the 18W is around 345V for the el84's whereas the amps with a good reputation for 6V6's like the champ and tweed deluxe have over 400V on the plates.
i would rather have a designated output tube and tweak that type to bring out the best.

That's a good point, but I'd love to see some actual voltage readings. They do have separate biasing in the schematic. Hey Craig, wanna take some voltages?

[geoff 1965]

a lot of area for variation here, i had a laney pro tube 30 "actually about 20W" which has a pair of 6V6's with exactly 400VDC on the plates and it had a good range of tones clean/overdriven but none of the touch sensitivity of the 18W el84,ironic because it's known as the "marshall killer"
i've been considering this preamp for my next build but with a designated plexi 6V6 phase & power section.

18Wattv6PlexiMkIISchematic13.pdf

[colossal]

I think there is a wide range of operating conditions that can make for a great sounding amp, even if not specifically spelled out in the tube datasheet. There are very few published applications to choose from anyway. High plate voltages would need to be tempered by an appropriate load line, screen voltages, and bias current.

[crgfrench]

Hey Craig, wanna take some voltages?

I would like to do that if I ever get around to opening it up. That's behind a queue of projects but if & when I get to that I'll post the results here.

[zaphod_phil]

Also Merlin (Valvewizard) says that what you hear in any amp is the power supply.

Yes, but I think it depends on the type of amp. I once designed and built a 6V6-based Hiwatt derivative, with the typically Hiwatt hifi-ish power stage. I did a lot of tests and found the power supply had a huge impact on the tone and feel of the amp. With other amps, IMO, not quite so much.

[fyzygy]

I have an old chassis with octal sockets, zero octal tubes to spare, a boxful of EL84s, and a couple of EL84>6V6 (noval>octal) socket adapters. To save myself the expense of removing and replacing the octal sockets, can I safely wire up the 18watt circuit to octal sockets and use the socket adapters with EL84s fitted? Would this allow me to be able to roll with 6V6s, in principle, at some point in the future, using the unmodified 18watt circuit? Or do components have to be changed in order to make a functional 6V6 version of 18watt? I haven't settled on a choice of power transformer, so current and voltage requirements could be worth thinking about. Any other issues?

[Bieworm]

The PI component values are different with 6V6 vs EL84. I don’t think you’ll yield good results when using the same values for both types of tubes

[JMPGuitars]

If their intent is to use EL84s, then they should design for EL84s, but match the pinouts for the 6V6 sockets. Or better yet, get new micalex noval sockets and some adapter plates and keep everything straight forward.