2-EL84 vs 4-El84 tone

[txbluesboy]

I never seem to be able to build a 4-el84 amp with as much sparkle/jangle as I can get from a 2-EL84 amp. Am I missing something or is this just the nature of the beast?

[billyz]

It is the " Miller Capacitance effect". Two tubes do sound better than Four.
http://www.aikenamps.com/MillerCapacitance.html

[gearhead]

EL-84's are pentodes.

[Alexo]

It is the " Miller Capacitance effect". Two tubes do sound better than Four.
http://www.aikenamps.com/MillerCapacitance.html

If you're using individual grid stoppers (which you probably should) won't that put you back where you started with 2?

[Zippy]

Funny, most of the conversation regarding the 1/2 power option on Tranwreck Liverpools and Rockets usually goes the other way - as does the same issue with Dumbles. The usual response is that 4-holers have a complexity that is lacking in amps with only one pair of output tubes.

I have often wondered whether the "complexity" is due to the added mismatch of response from the extra tubes. It isn't just due to the volume gained by adding an extra pair - there exist plenty of commentary that using a 1/2 power option doesn't net much of an audible difference.

[txbluesboy]

Thanks for your replies, but I'm more confused now than before.

[billyz]

Tube mismatch actually contributes to the Miller effect. Tetrodes and pentodes do suffer much less miller effect than Triodes, but it is not completely eliminated. Most of the Tube Hifi nuts believe multiple output tubes increase the Miller capacitance.
Some of the Conversations I have had with Mike Zaite led me to believe he thinks it has an effect . And he believes 2 tubes have less Miller capacitance than 4.
I don't think it is a huge problem, but there is an effect. If I wanted a 4 el84 or 4 6l6 or what ever. I would build it, but not expect it to sound like a bigger version of a 2 power tube design.

[Luthierwnc]

Having made a few of each, I'd say the biggest difference is the bottom end. On one 4X I put in a half power switch. Those EL84 are really loud for the actual power but switching from 4 to 2 (with corresponding impedance adjustments on the amp into a 2X12 cab) what you really notice is the low-end gets castrated. That might be the loss of jangle.

Skip

[Zippy]

Thanks Billy and Skip. This is a topic that I need to work on a lil' bit. Much appreciate your input.

[Alexo]

Don't forget that the frequency response of our hearing changes at different volumes, makes judging these changes rather difficult.

[Zippy]

As many have noted, there is not a great volume difference between the 2-EL84 and 4-EL84 configurations.

[Zippy]

As many have noted, there is not a great volume difference between the 2-EL84 and 4-EL84 configurations.

[txbluesboy]

One thing that might be part off it is that the 2-el84 amps I've built and really like are Matchless clones with 4K primary OTs. The Liverpool and Rocket clones are built with 5.2 or 6.6K primary OTs. Common sense would have us building the 4 tube versions with half the primary impedence of the 2 tube versions. 4 EL84 amps with 2K OTs. However Matchless uses 4K for both.

[Zippy]

You can always adjust the impedance switch or change speaker configurations to accommodate the difference.

[dartanion]

Matchless uses an impedance mismatch for the power sections as part of their tonal shaping. Normally, a pair of EL84s would be 8K primary (depending on your operating parameters) and a quad at 4K. Changing the impedance ratio in the OT changes the tone, hence you'll see various impedance ratios used across different amps that use the same output tube configuration.

The main differences to me between a 2 holer and 4 holer Liverpool is that the 2 holer breaks up faster and sounds more aggressive and the 4 holer sounds bigger (better bass response with the added power) and has more headroom. Both are plenty loud and you'd be hard pressed to tell which one has higher output.